Traits of invaded ecosystems? Are my compost worms a threat to New York? I was shocked to learn that there were few native worms in the glaciated portion of North America. I use worms indoors to compost paper and kitchen scraps. I don't think there is much chance of transfer as my garden is on the roof of an apartment. I was still surprised that my worms are essentially invaders in some parts of this country.

Thinking about all of this lead me to look up the damage done by non-native worms in North America. They have an impact on plants that once relied on the matted leaves on the forest floor. So, they can lead to more barren undergrowth. The native worms are not good at competing for some reason.

And I thought all worms were beneficial!

Still, before the most recent glaciers there were worms in these regions. So, why isn't this like turning the clock way back? In the end, after the glacier's impact fades, shouldn't there be a lot of worms again some day?

I guess sudden change is hardly ever desirable. But I'm very confused about how to identify an invaded ecosystem.
Is it just based on what humans notice? Has anyone tried to make the concept more objective?

The native worms are not good at competing for some reason.

There's a reason for that. There are no native earthworms in New York.

  Still, before the most recent glaciers there were worms in these regions.

North America has been hammered by multiple glaciations for the last two million years. It wasn't just the areas covered by ice that lost their earthworms. The northern forest, or taiga extended to the Gulf Coast at the peak of the last glaciation. You have to drive to Ontario to see the taiga now. The Great Plains were the mammoth steppe, very cold and very dry. Most of the US is depleted of native earthworms.

Invasive earthworms are your enemy if you like maple syrup. Sugar maples take a couple of years to germinate, and only need a nice pile of duff (leaf detritus that hasn't been consumed by earthworms) in which to do so.


How does one measure what causes earthquakes? I know that they occur when energy that was previously stored is released in seismic waves. But how is the energy stored in the earth in the first place, and what can trigger the release of such energy?

Put another way, the above preconditions for earthquakes can be brought about by natural phenomena such as fault lines in the earth, and also by man-made phenomena such as mining. What are the ways to measure/estimate the "potential" energy of a fault line, and the likely resulting earthquake, and what are the ways to measure/estimate the energy released by mining or other human activities, and how large an earthquake is likely to result?

There are a number of causes (this list is probably not complete):

Elastic Rebound of tectonic faults. This is the most common and well known. Here the energy is elastic energy stored as two blocks of rocks move against each other. There is a point where elastic deformation cannot take up the entire movement, and the rock breaks releasing the elastic energy. This is better explained here: Reid's Elastic Rebound Theory (USGS)
Landslides/etc. These typically appear as extremely shallow earthquakes and can often be determined from seismic records.
Cavity collapses. E.g. mines, volcanic systems, caves.
Subterranean explosions / volume expansion. Eg. mining activity, atom bomb tests, volcanic activity (eg. phreatic involving water; or magma injection)
Crystalline phase changes. Fast, deep subduction zones (eg. Tonga) experience very deep earthquakes where the rocks should be too plastic for classic elastic rebound. These are usually interpreted as 'catastrophic' phase changes of olivine -> spinel -> perovskite, and the depths generally match. Eg. Kirby 1991.


Difference in sun activity between two towns (Eastern and Western hemispheres) I grew up in a small town on a sea shore with hot and sunny summers (up to 30-35° C). I remember myself, my friends and relatives being outdoors for 12 hours a day. We never needed sunscreen, and never used it. It was considered, that skin can burn on the first day of taking a sunbath and precautions were taken, i.e. "put a long-sleeved shirt on after three hours in direct sunlight". Coordinates of my hometown are 46°45′35″N 36°47′04″E.

Currently, I live in another town, very close to an ocean shore, with coordinates 41°4′9″N 73°51′35″W, and we have hot and sunny summers (up to 30-35° C, sometimes a little bit more). I am very surprised how aggressive sun is here. We need sunscreen all summer long, and once I had to work outdoors for 8 hours at the beginning of September, and I somehow got a sunburn.

Given my childhood experience, it would be impossible for me to imagine, that I could get a sunburn at the end of summer. I simply used to get a very nice suntan over summer, and then my skin was resistant to sunburn. I wonder what is an explanation for this. One explanation could be that sun is more aggressive in my current town, than it was in my home town. But why? Another explanation, that there are some other factors involved, but I am not sure what these factors could be.

If anyone knows what is an explanation for this phenomenon, I would be most grateful for your help.

I believe this is biology related, not weather related

I think your story is a bit anecdotal because there is no measurable evidence that the sunlight energy deposited into your skin is actually stronger in New York as compared to Ukraine. Let me offer two lines of evidence that this change is more likely to be related to you and your skin than it is to the weather.

First, Rostov-on-Don, (the nearest large city I could find sunlight data for) has sunnier summers than New York. From NOAA via Wikipedia, Rostov has 286/314/293 hours of sunlight in June/July/August. New York has 257/268/268. This is largely because New York sees two more rainy days per month (and about twice as much rain on those rainy days) during the summer.

Sunlight intensity at a certain latitude is directly related to the angle of incidence of the sun. The declination of the sun is the relative angle from the sun to the horizon given your latitude and the time of year. The sun moves (well the Earth moves...) from the Tropic of Cancer to the Tropic of Capricorn each year, from 23.45 N to 23.45 S. During the northern hemisphere summer solstice, the sun is directly above the Tropic of Cancer. From New York, the angle of incidence of the sun is thus 41.07 N - 23.45 N =  17.62 degrees. During an equinox, when the sun is directly over the equator, the angle of incidence of the sun is 41.07 N - 0 = 41.07 degrees. The cosine of the angle of incidence is the percentage of full equatorial sunlight energy that you would receive at that latitude. Thus, in mid-summer in NY, you get cos(17.62) = 0.953 of maximum possible sunlight; at the equinox you get cos(41.07) = 0.754; at the winter solstice you get cos(64.52) = 0.430.

For any point in the Northern Hemisphere outside of the tropics, sunlight intensity will always be greater at all times of the year at lower latitude. Thus, New York always has greater sunlight intensity than Ukraine...but the difference is not very significant. At summer solstice NY gets 0.953 of the max sunlight, but Ukraine gets cos(23.3) = 0.918 of max sunlight. This is the difference between early July and mid-August in NY; not very significant. Given the close latitudes involved, you would expect to have gotten more net sun in the summer as a child than you do now due to fewer cloudy days. Since this is not what you observe, there must be some other explanation.

Secondly, I grew up near Boston, and my mom made me wear sunscreen in the summer. I used to get sunburns pretty bad. Now I'm 35 and I live in Virginia and I never wear sunscreen, even when I get to the beach. I don't remember the last time that I got a sunburn. Things change, I guess? This is a purely anecdotal observation, but then so is yours. Without any data to measure the changes (maybe I am smarter about being in shade in my older age?) all I can offer is guesses.

I think you should be looking at either your skin or your behavior as the cause of this change, not necessarily at the climate.


Is Earth getting heavier or lighter? There is meteoric material falling on the Earth constantly, as well as some protons and other light nuclei from the solar wind as well as from cosmic rays.

At the same time Earth's atmosphere looses gas to space, especially the lightest elements like hydrogen and helium.

Where does molecular hydrogen in the atmosphere come from? is currently unanswered.

Does one process dominate the rate of change of Earth's mass? Is Earth getting heavier or lighter?

tl;dr: The Earth receives 40,000 tons of dust from space every year, but looses 95,000 tons of Hydrogen and 1,600 tons of Helium every year as well. After all additional effects are balanced, the Earth looses about 50,000 tons a year.

It seems a similar question was asked in Astronomy Stack Exchange, and this short answer links to the BBC News article Who, What, Why: Is the Earth getting lighter? which answers this question.

There are factors that are causing Earth to both gain and lose mass over time, according to Dr Chris Smith, a medical microbiologist and broadcaster who tries to improve the public understanding of science.
Using some back-of-the-envelope-style calculations, Dr Smith, with help from physicist and Cambridge University colleague Dave Ansell, drew up a balance sheet of what's coming in, and what's going out. All figures are estimated.
By far the biggest contributor to the world's mass is the 40,000 tonnes of dust that is falling from space to Earth, says Dr Smith.

Surprisingly, General Relativistic effects of Global Warming is considered!

Nasa has calculated that the Earth is gaining energy due to rising temperatures. Dr Smith and his colleague Mr Ansell estimate this added energy increases the mass of Earth by a tiny amount - 160 tonnes.

Using $E=mc^2$ that works out to about $1.4 \times 10^{22}$ Joules/year or $4.6 \times 10^{14}$ Watts. That's about 3.6 Watts/meter^2 or about 0.3% of the total power coming from the Sun, so it does seem to be back-of-the-envelope-in-the ballpark correct!

But there is something else that is making the planet lose mass. Gases such as hydrogen are so light, they are escaping from the atmosphere.
"Physicists have shown that the Earth is losing about three kilograms of hydrogen gas every second. It's about 95,000 tonnes of hydrogen that the planet is losing every year.
"The other very light gas this is happening to is helium and there is much less of that around, so it's about 1,600 tonnes a year of helium that we lose."
So taking into account the gains and the losses, Dr Smith reckons the Earth is getting about 50,000 tonnes lighter a year, which is just less than half the gross weight of the Costa Concordia, the Italian cruise liner, that ran aground recently.


Alternatives to Plant Functional Types as parametrisations in land surface models? Plant Functional Types (PFTs) are a discretisation of global vegetation types. They are used in land surface models to parametrise many values, including albedo, various photosynthesis parameters, and water use. These affect the resultant estimates of Net Ecosystem Exchange of carbon (NEE), and heat and radiation budgets, and what happens to soil moisture. However, Alton (2011) has showed that for some of these parametrised variables, there is no significant difference between many commonly used PFTs. This means that PFTs may, in some cases, be a less than optimal method of deciding how each land surface model grid cell should operate.

Are there any alternative parametrisations of the global land surface that could provide more, or better information to land surface models? Perhaps based on soil types, or even statistical parametrisations (like something PCA based)? If so, are any in use in any current land surface models?

Alton, P.B., 2011. How useful are plant functional types in global simulations of the carbon, water, and energy cycles? Journal of Geophysical Research, 116(G1). Available at: http://doi.wiley.com/10.1029/2010JG001430 [Accessed August 26, 2013].

The approach used by Alton et al 2011 is appropriate for the scope and intent of this paper - to demonstrate a weakness in the approach - but is not a comprehensive analysis of PFTs in models.

I think it is useful to question the use of PFTs but incorrect to conclude that Alton et al claim PFTs are not useful. Alton et al show that albedo, net shortwave radiation, and runoff are insensitive to PFT-specific values of four parameters, but they also find that net carbon balance is sensitive.

The study's conclusions are limited to the JULES model that is evaluated and the parameters that are allowed to vary (and thus be estimated by inversion). There are many different models of terrestrial ecosystem functioning, and many approaches to model parameterization. Furthermore, JULES has more than 50 parameters for each PFT, and only four were varied in this study. (This is the number of parameters set in JULES' fortran namelist under JULES_NVEGPARM and JULES_PFTPARM).

This study also provides examples of how inversion using what are essentially 'free' parameters (analogous to 'flat priors' in a Bayesian context) has limitations. Fig 3 shows this, since the 'retrieved' (inverse-estimated) parameters are inconsistent with direct measurements of these parameters. This is more of a limitation of the inversion approach for estimating PFT-level parameters than of the utility of PFTs as an approximation of plant physiological diversity.

To answer your question - yes, there are alternative approaches to both model structure and parameterization. This is an active area of research (and one I am interested in). Here are some examples, in order of increasing complexity (and data and computational requirements).

Global land surface models like JULES are necessarily more abstract (and use PFTs to represent a 'Biome').
Represent groups of individuals that belong to a particular PFT and age class (This was first done in the Ecosystem Demography model (Moorecroft et al 2001, which has both evolved to ED2 and has been integrated into NCAR's Community Land Model.
Vary parameters dynamically in both space and time. For example, Wang et al 2012 show that varying Vcmax in (vertical) space and time improve estimates of gross primary productivity in a very simple crop model.
Individual Based Models (IBM's) represent individuals explicitly. These are reviewed by DeAngelis and Mooij 2005.
Using probability distributions to reflect parameter variability in the system being studied. I am not aware that this has been attempted.

However, adding more degrees of freedom limits inference - too many unconstrained parameters make it difficult to parameterize the model, understand its output, or make general conclusions about how the world operates.

Remember "All models are wrong, but some are useful" - George Box

Wang et al 2012 Impact of nitrogen allocation on growth and
photosynthesis of Miscanthus (Miscanthus x giganteus). Global Change Biology - Bioenergy. doi:10.1111/j.1757-1707.2012.01167.x
P. R. Moorcroft, G. C. Hurtt, and S. W. Pacala 2001. A Method for Scaling Vegetation Dynamics: the Ecosystem Demography (ED) Model. Ecological Monographs 71:557–586. doi:10.1890/0012-9615(2001)071[0557:AMFSVD]2.0.CO;2
DeAngelis and Mooij. 2005. Individual-Based Modeling of Ecological and Evolutionary Processes. Annual Review of Ecology, Evolution, and Systematics. doi:10.1 146/annurev.ecolsys.36.1020


Ways, Through Science, to Counteract Hurricane Forces? I know nothing significant about meteorology and definitely not a science guy so this will probably seem naive...

But today I am wondering if there is any existing science or methods a government (with enough funds) could employ, through science, to lessen the force of a hurricane?

I vaguely remember something about them being affected by air temperatures, so couldn't something be done to somehow inject heat or refrigeration into the area? Or something to counteract against it's speed increases?

What approaches would one consider in such an endeavor?

It might be possible but hasn't been done in practice
One idea is that smoke could be introduced into the hurricane and, because the smoke is heavier than air, the wind speeds could be reduced.
The smoke would also cause water vapour to condense at lower altitudes and hamper the heat cycle within a hurricane. When the water evaporates it carries with it the energy needed to heat it to that point. The water vapour is lighter than air and will rise but once it condenses it falls - releasing the energy it gained from rising (like if you pushed a ball up a hill), this energy adds to the air currents within the hurricane. If the water condenses at a lower altitude it doesn't have as much energy.
There are other ideas such as using fans to blow in cool air and seeding clouds with silver iodide (link makes for an interesting read but ultimately failed), these ideas may also have some potential but one of the problems with altering complex weather systems is that the side effects are not necessarily well understood. This makes carrying out practical tests difficult on both a moral and legal level.


What actually happens to reduce the perceived color in a 'white rainbow" or "fog-bow"? The image below is included in the BBC article Amazing white rainbow snapped over Scottish moor. Apparently this phenomenon is sometimes called a "fog-bow" and is characterized by the washing out of perceived color relative to a conventional rainbow.

Is this related to the geometry (fog being far closer to the viewer) or properties of the droplets themselves? If so, which properties and why?

Higher resolution in flickr

The reason why fog bows lack colour, compared to rainbows, is due to the size of the drops of water.

Fog is composed of very small drops of water - less than 0.05 mm diameter. Because of this the wavelength of light is critical, with diffraction smearing out colours that the larger drops of water in a rainbow would make.


WRF/Chem: Editing NetCDF (wrfchemi files) for own emissions Does anybody here have any experience with editing wrfchemi outputs from the prep_chem utility so that I overwrite the file with my own emissions?

I am knowledgeable in python, but I am not that well oriented with the manipulation of NetCDF files.

What I want to do, basically, is to use my own emissions inside the WRF/Chem model

I have a shapefile of emissions (gridded) with each grid having a value for the emissions.
I want to convert this to a readable format for the WRF/Chem; however, I think editing the wrfchemi files by prep_chem would be easier? (Tell me if not)

I have read the emissions guide of the WRF/Chem, but it does not really expound on details about this especially about the following

How to deal with the speciation (my shapefile has only PM10 and PM2.5). where exactly do I place this in the new emissions file (the edited wrfchemi)I want. There are many pm species there (like pm2.5 nucleation mode, pm, etc). I am not sure what weights to put on these.
My emissions are not time dependent, and what do I do when I edit the wrfchemi file for this. (the wrfchemi files I have now are also not time dependent)

Hoping someone could help out with this.

Thanks!

You can try the R package eixport, with wrf_put

# example
# Read the array emissions,
CO <- wrf_get(file = "Path_to_WRFCHEMI", name = "E_CO")
# Change the values, here you should use your data
CO[] = rnorm(length(CO))
# Inyect your emissions into the wrfchemi
wrf_put(file = "Path_to_WRFCHEMI", name = "E_CO", POL = CO)

  How to deal with the speciation (my shapefile has only PM10 and
  PM2.5). where exactly do I place this in the new emissions file (the
  edited wrfchemi)I want. There are many pm species there (like pm2.5
  nucleation mode, pm, etc). I am not sure what weights to put on these.

You need to know the speciation for your local. At my department at Uni. of São Paulo, we use the following speciation of PM 2.5 (g/h/km^2)

e_so4i = 0.0077, e_so4j = 0.0623, e_no3i = 0.00247, e_no3j = 0.01053, e_pm2.5i = 0.1, e_pm2.5j = 0.3, e_orgi = 0.0304, e_orgj = 0.1296, e_eci = 0.056, e_ecj = 0.024, h2o = 0.277

Check this

  My emissions are not time dependent, and what do I do when I edit the
  wrfchemi file for this. (the wrfchemi files I have now are also not
  time dependent)

You need to first edit the namelist.wps and namelist.input to the desired length of time. Then, after running  ./real.exe you will have the wrfinput_d0x. At this stage you can use wrf_create which creates a wrfchemi file with 0. Read the manual to see if you want two 0-12z 12-0z files or one file with the length for all hours. Then you can use wrf_put. Just follow the example and read the manual.

You might also try the R package EmissV

References:

Ibarra-Espinosa et al., (2018). eixport: An R package to export
emissions to atmospheric models. Journal of Open Source Software,
3(24), 607, https://doi.org/10.21105/joss.00607 Schuch et al.,
(2018).
EmissV: an R package to create vehicular and other emissions
for air quality models. Journal of Open Source Software, 3(30), 662,
https://doi.org/10.21105/joss.00662


How global was the Bonarelli Oceanic Anoxic Event? The Bonarelli Event (a.k.a. OAE2) is a well-studied episode of "worldwide" oceanic anoxic event at the Cenomanian-Turonian boundary (ca. 94 Ma). It is characterized by the presence of organic-rich marine sediments and a $\mathrm{\delta^{13}C}$ shift. It is thought to have provoked a minor mass extinction and an increased atmospheric and oceanic temperature.

What evidence do we have that the anoxia was indeed global?
Is there really no known ocean basin with sediments spanning this time interval that doesn't show those characteristic black shales?

Recent research and models, based on sulphur and carbon radioisotope data, reported in the article Sulfur isotopes track the global extent and dynamics of euxinia during Cretaceous Oceanic Anoxic Event 2 (Owens et al. 2013) suggest that the oxygen-free and hydrogen sulfide-rich waters extended across roughly 5% of the global ocean, compared to <<1% today.

Owens et al. model results place important controls on local conditions, rather than global conditions and point to the difficulty in sustaining whole-ocean euxinia.

The models based on the sulphur and carbon isotopes suggest that

  the excursions were driven by increased burial of pyrite and OC. Although generally coupled, these C- and S-isotope excursions show a pronounced offset between peak magnitudes. The observed offset between these isotope signatures may not be unique in the geologic record but is certainly a pronounced characteristic of OAE 2.

and crucially, in terms of local over global controls,

  The spatial variability in the excursion magnitudes could be due to local watermass differences and/or varying riverine fluxes to an ocean with substantially lower than modern sulfate concentrations, an effect noted also for the Toarcian OAE*

Further explanations are provided in the article Marine $\mathrm{^{187}Os/^{188}Os}$ isotope stratigraphy reveals the interaction
of volcanism and ocean circulation during Oceanic Anoxic Event 2 (du Vivier et al. 2014), who found that, through analysis of marine $\mathrm{^{187}Os/^{188}Os}$ isotope stratigraphy

  differential input of nutrients from continental and volcanogenic
  sources, coupled with efficient palaeocirculation of the global ocean and epeiric seas, enhanced
  productivity due to higher nutrient availability, which permitted penecontemporaneous transport of
  continental and LIP-derived nutrients to trans-equatorial basins.

LIP = Large Igneous Provinces

and that the tipping point was rising sea levels at the time, further, the authors suggest that from local sources and igneous activity, coupled with rising sea levels and palaeo-oceanic circulation at the time, concluding with the evidence suggesting a global reach of the anoxic event:

  The close similarity of $\mathrm{Os_i}$ profiles from ∼50 kyr prior to the OAE 2 and through out the syn-OAE 2 interval indicates that transgression progressed to a point where a homogeneous global seawater signal was delivered to  multiple proto-transatlantic basins by active ocean circulation.

This suggests that the anoxic event started locally with weathering from the land surface, coupled with large igneous province (LIP) activity, progressing due to rising sea levels and palaeo-oceanic circulation.

Additional references

*Newton et al. 2013, Low marine sulfate concentrations and the isolation of the European epicontinental sea during the Early Jurassic


Why is Earth's inner core solid? I have never understood why earth's inner core is solid.  Considering that the inner core is made of an iron-nickel alloy (melting point around 1350 C to 1600 C) and the temperature of the inner core is approximately 5430 C (about the temperature of the surface of the sun). Since Earth's core is nearly 3-4 times the melting point of iron-nickel alloys how can it possibly be solid?

Earth's inner core is solid even though the temperature is so high because the pressure is also very high.  According to the Wikipedia article on the Earth's inner core, the temperature at the center is $5,700\ \text{K}$ and the pressure is estimated to be $330$ to $360\ \text{GPa}$ ($\sim3\cdot10^{6}\ \text{atm}$).

The phase diagram shown below (taken from this paper) shows the liquid/solid transition, where fcc and hcp are two different crystalline forms of solid iron.  You can see clearly from the slope of the line going off toward the upper right that iron should be solid at this temperature and pressure.


What is the meaning of the units Mg C? I am reading an article on deforestation entitled Tropical Deforestation and Carbon Emissions from PADDD. Part of the article reads:

  If future deforestation rates follow recent trends, PADDDed forests would emit approximately 6.0–10.9 million Mg C by 2100.

What is the meaning of Mg C? Is it milligrams of carbon?

Mg C is a tonne of Carbon.

An Mg - a megagramme - is a tonne. It's a silly way of writing a tonne for a general readership, but it's the strict SI equivalent of a tonne. So an "Mg C" is a tonne of Carbon - the standard unit when it comes to talking about pricing Carbon.

Normally you wouldn't see anyone writing about a million Mg of anything; (in this case, of carbon). You'd either write about a Teragramme, or a million tonnes, but not a million Mg.

However, if you draft a paper referring to millions of tonnes, and then the editor or a peer reviewer comes back and says that the tonne is not a strict SI unit but the Mg is, then someone in the chain of authors and editors may just do a search and replace on all the "tonnes" to replace them with "Mg". And that's one way that you might end up with lots of references to "million Mg C", instead of the more usual "million tonnes of carbon"


How Do Plateaus Really Form? Any time I hear the word "plateau", I usually associate it with the tallest in the world, Tibet.  Anyone who looks closely at a map will see that the southern line of the plateau parallels the location and length of the Himalayas, leading to the assumption that the collision between India and mainland Asia, which resulted in the formation of the Himalayas, also forced Tibet upwards, creating the highest great plain on Earth.

But as the link here shows, it's not so simple.

The Altiplano is classified as a plateau, yet it does not span the entire length of the entire Andes, the longest mountain range in the world.  Nor does the Colorado parallel the whole length of the Rockies.

So if a plateau is not formed as originally lowlands forced upwards by nearby mountain-building, then how does it REALLY form?

First of all, a plateau as an area of flat topography which stands at higher elevation than the surrounding region; it does not need to be at high elevation in absolute terms. Indeed, there are plateaux below sea level.

There are several different processes at the origin of the plateaux in the map you link.

Some, such as the Deccan and the Columbia plateau, are the results of infill of volcanic rocks in an accomodation space during voluminous volcanic eruptions, called "flood basalts". These flood basalts effectively flow into topographic depressions, thus flattening the topography and resulting in a plateau.
Note that there are also oceanic plateaux which are formed by large magma outpours- they are usually below sea level. Examples of this are the Caribbean Oceanic Plateau and the Ontong-Java plateau.

Other plateaux such as the Altiplano and Loess plateau appear to be a result of basin infill by mainly sedimentary processes, either by water or wind transport. Past erosion removed material from topographic highs and dumped it in topographic lows, thus flattening out the relief. This is effectively a peneplenation process operating locally.

Although the high elevation of the Tibetan plateau is undoubtedly due to tectonic uplift, the cause of flat topography appears is likely to reflect relief reduction by combined erosion and deposition as above. It is unclear whether this was an ancient peneplain which was pushed upwards, or a more recent feature.


How would plate tectonics differ if Earth had no water? Water plays a crucial role in plate tectonics by easing the brittle and ductile deformation of the Earth's lithosphere. Water lowers the Mohr-Coulomb for brittle fractures. During ductile deformation, it lubricates different deformational regimes. This is also important for the deformation in the asthenosphere.

In addition, water plays an important role in the formation of water-bearing minerals and the fluxing of melts, thereby substantially changing the rheology of the lithosphere and asthenosphere.

So, what would plate tectonics look like on a waterless Earth? Would it even work? Would there be different rates, or totally different processes taking over, similar to what is seen on adjacent solar system bodies?

Sources:
V.S. Solomatov. The role of liquid water in maintaining plate tectonics and the regulation of surface temperature

See also:
Plate tectonics and water

One way of looking at this question is to determine if Earth would possess an active-lid (multiple plate), stagnant-lid (single plate) or an intermediary state (e.g. episodic or sluggish) tectonic regime.  This is one of the reasons comparisons are often made with Venus, especially in regards to the main difference been that Venus has a stagnant-lid with possible episodic active tectonic regime (see question and answer to Can Venus be considered to be tectonically active?, compared to Earth's active-lid tectonic regime.

However, there are other differences between Venus and Earth that also may account for the differences in tectonic regimes, asides from the relative absence of water on Venus. Some modelling by Bouffard, (2013) indicated that different plastic yield strengths of lithospheric rheology could account for the different tectonic regimes.

How water interacts oceanic lithosphere is a vital consideration for this kind of question, considering that most spreading ridges and all subduction zones are based on the oceanic lithosphere.

This answer is based on how the absence of water may have prevented a key theorised tectonic mechanism from even starting.

A crucial role for water is modelled by Regenauer et al. (2001) for the initiation of subduction and as they assert the beginning of plate tectonics, based on the theory that long term build up of sediment at a passive continental-oceanic boundary (e.g North American east coast) may have caused the strain to build up to a point where the oceanic crust 'breaks' and starts subducting, as shown in the diagram below:

Image source

In the absence of water, this process of subduction initiation (should it be true) could not have started; as the authors believe could be the case for Venus where volcanism is evident, but the mechanism appears to be hotspot activity through the current stagnant-lid tectonic regime observed there - if this theory were true, then the absence of water would mean that Earth would potentially have had a stagnant-lid, punctured by hotspot activity.

References

Bouffard, 2013, Role of water in the tectonics of Earth and Venus, University of Lyon

Regenaeur et al. 2001, The Initiation of Subduction: Criticality by Addition of Water? Science


Are high velocity winds, or the lack of wind, the most common cause for low visibility? Low visibility, say <1km (3300 ft), can be caused by fog when there is no/little wind present.  On the other hand, high winds associated with blizzards or wildfires can also create low visibility environments.  Living in a temperate climate I'd be inclined to believe that a lack of wind is the most likely cause because fog seems to be more common, however I'm not sure if this would be the case when other latitudes are also taken into consideration.

Light or calm winds do not cause reductions in visibility, but stronger winds will generally be associated with better visibilities. Poor visibility is more likely in a humid, polluted air-mass than a clean dry air-mass.

Reductions in ‘visibility’ or visual range are caused by the scattering and absorption of radiation by atmospheric particulates or aerosols. This attenuation of radiation will depend on the type, size and concentration of these particulates or aerosols. In a humid airmass water droplets can form on certain types of aerosols and these droplets can increase in size as humidity increases.

Strong winds will tend to mix the polluted air near the surface with cleaner air aloft. This mixing will also create a more uniform profile of temperature and humidity in the lowest portion of the atmosphere. If there are light winds overnight, the air near the surface becomes cooler and more humid than the air aloft. The pollutants become concentrated in this cool stable layer of air near the surface.

There are exceptions, namely advection or coastal fog. In far north-east of the U.K it’s not that uncommon to see fog with 20-30 mph winds during late spring and early summer.

https://www.metoffice.gov.uk/learning/fog


How long does it take to form amber? How long does the formation of the amber take? Are there any approximation of the minimal time needed to convert resin into amber in the most favorable conditions?

Would it be possible to produce amber on the timescale of a human lifespan?

In Schmidt & Dilcher 2007, the authors were interested specifically on how amber can trap aquatic organism, so this is a specific, out-of-the-norm case study but it might give you at least on order of magnitude. Here is an extract:

  Within the first day or two after initial contact with water, all
  three resin fractions were traps for limnetic organisms. The resinous
  film at the surface then dried out and broke into small
  centimeter-sized fragments, so no long-term preservation can be
  expected for this exudate. The pieces of resin hanging at the water
  surface became more and more solid within a few days because of air
  contact at their upper surface. After 1 week, these pieces were nearly
  solidified (Fig. 1 D).

And later:

  In contrast, the large resin bodies on the ground did not solidify as
  long as they were covered with water. But this resin was also
  initially a trap for microorganisms before a thin hardened skin
  developed at the resin surface after 1 or 2 days in the water, which
  prevented tiny organisms from getting stuck. Nonetheless, the resin
  remained liquid inside, and therefore large arthropods that were able
  to break through this skin could become entrapped over a couple of
  weeks. [...] The resin solidified when exposed to the air in the
  laboratory or by decreasing water level in the swamp during the
  summer.

So the polymerization process to go from resin to solidified resin (copal) takes weeks. At that point, the system is already closed meaning the contained organisms correspond to that time interval.

The next step (amberification) consists of further polymerization as well as oxydation and can take several million years (Poinar 1992). However the minimum time needed for this process is unknown.

Reference:
Poinar Jr, 1992. Life in amber. Stanford University Press.
Schmidt A. R. & Dilcher D. L., 2007. Aquatic organisms as amber inclusions and examples from a modern swamp forest. PNAS, 104(42): 16581-16585.


What are Ordovican trace fossils, and what do they look like? There are some unusual structures in recent images from the Mars Curiosity Rover's MAHLI (Mars Hand Lens Imager) shown in the Space.com article Curiosity Rover Spots Weird Tube-Like Structures on Mars.

An astrobiologist (not at NASA) is quoted as saying that they looked "...remarkably similar to Ordovician trace fossils..." while others are quoted as suggesting that these are visually reminiscent of bioturbation processes on Earth.

Question: What are Ordovician trace fossils and bioturbation, and what do they look like on Earth?

  below: NASA's Mars rover Curiosity captured this image on Jan. 2, 2018, with its Mars Hand Lens Imager (MAHLI). Using an onboard focusing process, the robot created this product by merging two to eight images previously taken by MAHLI, which is located on the turret at the end of the rover's robotic arm. Credit: NASA/JPL-Caltech/MSSS

Cropped section are also included for better viewing, in the first one, sunlight can be seen below the structure near the bottom, showing that it extends somewhat upward from the rock below it.

  below: Curiosity Mastcam right image taken on Dec. 15, 2017. Credit: NASA/JPL-Caltech/MSSS

Trace fossils are marks or things left behind by living things do their thing,  they are indirect remains of organisms, coprolites (poop), footprints, egg shells, ect. If we found a fossilized beehive or beaver dam those would also be trace fossils. Bioturbation is a specific type of traces fossil, marks of disturbances of the sediment itself animals leave behind, trackways and burrows are the classics.
Identifying bioturbation is tricky in a lot of cases, there are thousands of kinds which makes it worse, there is no way to give a direct answer. Your best bet is to find out what particular bioturbation they are referring to.  Burrows, trackways, feeding trails, nest, hold marks the list is endless. there are nearly as many trace fossils as there are organisms that crawl or dig.  Worse they are often very contextual and need examination of  micro-structure.  What is obvious a trace fossil in one formation will look identical to the naked untrained eye to something that is obviously not a trace fossil in a different formation. Generally you want to a specialized experts opinion before if saying something might be bioturbation someplace you don't expect it.
Even from a single location you can have a wide variety of forms,  here are a few examples from the ordovician, ...the second of six periods of the Paleozoic Era, 485.4–443.8 million years ago.
Bioturbation

The photos from mars are not likely to be bioturbation but are almost certainly differential erosion of normal chemical variation in rock. They do not have any of the characteristics that scream "this has to be biological activity" like cross cutting bedding planes or parallel patterns. Sedimentary rocks are rarely homogenous and chemical processes combine with erosional ones can produce some weird results. for comparison here are a few things that are definitely NOT fossils.
**Pseudofossils AKA Leaverite **

Pseudofossils are things lake look like fossils to the untrained eye but are just rocks, usually the leftovers of a chemical or erosional process. the term leaverite comes from geologists telling others "just leave're there"


How does high rate of evapo-transpiration contribute to the ineffectiveness of rainfall? If evapo-transpiration is high then more water vapor is taken up to the atmosphere and more condensation takes place resulting in more rainfall. But in the book The Environment of Pakistan by Huma Naz Sethi, she writes that high rate of evapo-transpiration is a consequence of ineffectiveness of rainfall.

I do not understand this. How does high evapo-transpiration contribute to less rainfall?

I just read the paragraph about the Effectiveness of Rainfall in UNIT.2 Climate of Pakistan, p. 30.

The author bring the topic of the rain being ineffective in a context where the rain is expected for crops and farming, or in other words, on the potential usefulness of the said rain for crops, which is quite low considering the climatic context in this area. I do not think the author is trying to explain the actual process of evapotranspiration for the area.

This is a summary of the factors bring by the author on why the current pluvial regime on Pakistan is not 'effective':

Rainfall is mainly from monsoon. Monsoon rain is not regular (and therefore unreliable for planning long term with rain as an only source of water). For instance ,distribution, amount and timing varies.
High temperatures during the monsoon season imply high potential evapotranspiration so a greater proportion of the rainfall is evaporated rather than infiltrated to be available for crop growth
Rain when it occurs is quite intense, with often a low infiltration rate and flow away instead of recharging ground moisture
Insufficient rain during winter to compensate

Therefore, irrigation and other means to store and distribute water should be used in the long term to efficiently use the water input, in regard with the potential use for water.


What determines the scale of columnar jointing? What physical parameters determine the scale of columnar jointing?

What makes the columns thinner or thicker?
What makes them taller or shorter?
What causes the variation in a given site?
What makes the polygons more/less regular?

I'm guessing factors include internal temperature, cooling timescales, composition, etc, but the literature seems to be a little uncertain.

Related questions and answers on StackExchange emphasize the formation processes, but they do not directly address the scaling:

What processes produced the basalt columns of the Giant's Causeway?
Basalt vs. columnar basalt

There is a paper about this in the Bulletin of Volcanology (Hetényi et al. 2012).

Cooling rate seems to be the main parameter controlling column size (faster cooling yielding to thinner columns). According to the authors, cooling rate is itself controlled by two non-independent factors: (1) the geometry of the lava body, and (2) the chemical composition of the lava.

(1) Geometry of the lava body influences the boundary conditions for cooling, depending on the emplacement setting (air, host rock, ice...). In the case of a lava lake (figure 2b), lava close to the lake walls will cool faster than lava at the centre of the lake, resulting in thinner columns. Thickness also plays a major role, as shown by figure 10: thicker lava bodies cool slowly, generating thicker columns.

(2) Chemistry plays a role (figure 11): felsic (SiO2-rich) lavas tend to have thicker columns than mafic lavas. It seems a bit counter-intuitive, as felsic lavas are usually emplaced at a "low" temperature and should thus cool faster than a basalt emplaced at 1200 °C... But felsic lavas are more viscous and tend to form thicker flows -> back to (1).


The grains of the parabolic dunes My text book says that parabolic dunes consist of consolidated limestone grains, but I wondered if  they have sand grains too, so I googled this issue and found that they consist of sands, but I am still perplexed, do parabolic dunes have both sand and consolidated limestone grains or they only contain one type of grains? And do they form exactly as other types of dunes (barchan dunes for example)?

"Sand" is generally made up of whatever eroded rock type is nearby, minus the most easily eroded (and windswept) components. Typically, dunes are made up of highly resistant quartz grains, like the stuff that blows off of white sand beaches, for example, or feldspar sands which are even more erosion resistant (in certain cases). There are also very soft white gypsum sands in New Mexico who owe their existence to a nearby, inexhaustible supply of gypsum evaporites.

As for limestone sands, I've never heard of it although it's certainly possible given very specific circumstances. Nevertheless, that's not what controls dune morphology. Dune shape is almost entirely controlled by both wind and sand supply and similarly shaped dunes will occur regardless of grain composition if dune-forming components are the same.


Electricity in clouds and induced magnetism This is well known to everyone that clouds carry electric charges and cumulonimbus clouds contain huge amount of electricity. It is also known from Maxwell's equations that moving particles induce magnetic field around them. I am sorry if I am missing any concept here but I have a question,

  Should there also be a magnetic field around cumulonimbus clouds due
  to the presence and motion of charged particles in them?

Edit:

I want to know about field studies reporting the intensity of the magnetic field in different cloud systems. I am interested in knowing about cold clouds as the interaction of solid hydrometeors could be prominent in them. I also want to know if the intensity is sufficient enough to have an interaction with magnetic field of earth. I see recent modeling studies are being performed on electric fields, but the mention of magnetic field is still missing in them.

The short answer to your question is yes all charge particles (positive or negative), independent (like electron, proton) or attached to other materials like cloud droplets, molecules, atoms, etc. when in motion produce magnetic field.

If two charged particles of same charge are moving in opposite direction then they cancel out each other's magnetic field. Hence, the random motion of droplets in cloud cause net zero magnetic field away from the cloud. One can understand this by analogy to a pair of electric wires used in powering homes which does not produce appreciable magnetic field at distance when the two wires of pair are close to each other because electrons are moving in opposite directions in the two wires.
In organized motion of charged particles that is when there is net movement of charge in a preferential direction, for example a cloud with charged droplets moving under influence of wind one can have net magnetic field. However, here too, if the cloud as whole contains both positive and negative charges in equal numbers will not produce appreciable magnetic field at a long distance because magnetic field produced by negative charges will be opposite in direction with respect to magnetic field produced by positive charge moving in same direction. If there is net positive or negative charge on cloud then the magnitude of magnetic field will depend on wind speed, which for atmospheric range of wind speeds will produce very small magnetic field.
The appreciable magnitude of magnetic field is produced during lighting since large amount of charge moves along a particular path with high velocity but such movements are momentary and as soon as the lighting strike is over, the magnetic field produced starts dying. If a compass needle is having significant inertia then before the needle can move under influence of newly produced magnetic field, the magnetic field will vanish and hence ordinary compasses are unlikely to show effect of lightning strikes.

Further Reading:

Fundamentals of Lightning by Vladimir A. Rakov, Cambridge Univesity Press, ISBN 978-1-107-07223-7, 2016


How deep are the cracks in the earths crust at fault zones? I have seen pictures of the cracks in the Earth's crust in Iceland and the San Andreas fault. To my eyes, the crack is relatively wide at the surface than a few meters down seems to be very narrow or just not there. I know this might seem stupid, but how come the crack does no go all the way down to the mantle? Is it that the crack opens and then the soft rock down below slides over to fill it in again?

How deep are the cracks at fault zones, I am thinking of the Silfra crack in Iceland between Europe and the US.

Cracks (actually the right word is fault or in some situations rift) can only occur in brittle material and only the Earths upper crust (top 5-25 km) is brittle. The lower crust and mantle are ductile, i.e., they have a relatively lower viscosity which means that they can indeed crack on short time scales but will heal quickly due to high temperatures and pressure.

Edit: In some ways you can think the lower crust and mantle to be like pitch (tar), which is solid at room temperature but flows over longer periods. E.g., see this link which also happens to be the worlds longest running experiment.


Is the Unified Theory of Climate (Nikolov & Zeller) compatible with the AGW/GHG theory in any respect? Nikolov & Zeller have published a paper concerning what they call The Unified Theory of Climate.

https://www.omicsonline.org/open-access/New-Insights-on-the-Physical-Nature-of-the-Atmospheric-Greenhouse-Effect-Deduced-from-an-Empirical-Planetary-Temperature-Model.pdf

Please read the paper in full and then answer my question.

Personally I can see no areas in which the new theory is compatible with the current theory of the Greenhouse Gas Effect and Anthropogenic Global Warming however there are some extremely knowledgeable participants on this site so I welcome their input but only, please, if you have read the whole paper.

The paper you linked lists as its first reference Volokin and ReLlez, 2014; a paper that addresses the magnitude of the Earth's greenhouse effect. The validity of the paper you found largely hinges on the reputation of the Volokin and ReLlez, so we will investigate that one first.

The science of Volokin and ReLlez

The traditional way to determine the 'greenhouse effect' of a planet is to compare actual planetary temperatures with Stefan-Boltzmann blackbody temperature based on the luminosity of the star, distance from star, and the albedo and emissivity of the planet. This calculation is done in Volokin and ReLlez and can also be found on Wikipedia.

Volokin and ReLlez are arguing that the actual greenhouse effect should be measured using the albedo of a bare planet stripped of its clouds. The Earth's albedo is 0.294, but they propose a bare albedo of the Earth of between 0.122 and 0.13. They then make an argument that simple albedo calculations are not very accurate, and that a use of Holder's Inequality should be used to integrate the effects of albedo and radiation incidence angle over the exposed surface of the bare planet. Redoing the Stefan-Boltzmann expected temperature calculations with this new method, they then calculate that actual 'greenhouse effect' of the Earth is more like 90 K, instead of the 33 K normally cited. This is significant because temperature magnitude of the Earth's greenhouse effect affects the climate sensitivity factor of global warming models.

I actually think this paper is pretty interesting. The core of its mathematical arguments seems valid (though I didn't try to work any of it out myself) However, the conclusions are not very good, and not very related to much of the mathematical arguments in the body. While there is an argument to be made that calculating expected surface temperature should assume a bare planet, the authors are basically concluding that all temperature differences between the bare planet and the observed Earth should be assigned to the greenhouse effect. That just isn't supported by the information they present. The Earth's actual atmosphere and biosphere are much more dynamic than the bare model they are presenting; the formation of high-albedo clouds by equatorial rainforests,and the presence of high-albedo sand in the sunniest places on Earth are just two non-greenhouse related effects that account for temperature differences between the author's ideal bare Earth and the real Earth.

While they consider a lot of interesting factors, I think Volokin and ReLlez are guilty of making too much of a spherical cow estimate. The author's make an argument for one thing, then make some huge leaps to an unsupported conclusion. All in all, I don't think that the author's conclusion of a 90 K greenhouse effect is valid.

The publication of the reference

Whatever its scientific merits, the paper doesn't look very good upon meta review. First off, the authors used fake names to publish the paper in an open access site. In fact, it is the same two authors of the paper you linked, except that they spelled their names backwards (Nikolov -> Volokin; Zeller -> ReLlez). Ummm...what? Also, they later retracted the paper. Also also, the journal they published in is now defunct. All in all, this is not a sign that the paper is good science.

Back to the original paper

So the paper that you are asking about (Nikolov and Zeller, 2017) is based on a paper by the same authors which has not-very-good conclusions, and was generally published in a shady manner. That's a big black mark at the very outset.

This paper is pretty long and detailed, and I admit I did not read all of it. But the kill shot for me was on the very first page:

  We  began  our  study  with  the  premise  that  processes
  controlling   the  Global  Mean  Annual  near-surface  Temperature
  (GMAT)  of  Earth   are  also  responsible  for  creating  the
  observed  pattern  of  planetary   temperatures across the Solar
  System. Thus, our working hypothesis was  that  a  general  physical
  model  should  exist,  which  accurately  describes   equilibrium
  GMATs  of  planets  using  a  common  set  of  drivers.

That is great, but we have already gone over how these authors are attempting to oversimplify a bare planet approach for predicting expected temperatures. The predictor variables they are using are stellar irradiance, blackbody reference temperature, greenhouse gas partial pressure and density, atmospheric pressure and density, and reference pressure for greenhouse fluids. We can see the authors are once again ignoring the effects of cloud formation and the way the biosphere affects albedo, amongst other things.

On a methodology note, the authors use a regression model to try to get some useful results. As a statistician (not a planetary scientist), this strikes me as a poor choice. Regression analysis of complex systems is a good way to get insight into what factors are important in affecting this system. I think they can be very useful for predicting trends, but I do not believe they are good for providing predictions that are accurate by physical science standards.

For example, I'm writing a paper right now that uses regression analysis to predict subway ridership at each station on a subway network. This is a very complex system (like planetary atmospheres), and our goal is to get error scores of 0.2 or so. That is great for predicting subway ridership, not so much for planetary temperatures. An error score of 0.2 is like predicting a temperature to be 300 K but it is actually 360 K. That's not good enough. So I just don't know what the authors are really trying to accomplish using a regression approach, especially with so few predictor variables. The physics behind the interaction of the predictor variables is pretty well known, so there isn't a lot of value if determining the correlations of the predictor values to the planet surface temperature; it is as if they are using the regression to test if the physics is correct. Finally, the data set is way too small to be using a regression analysis. Their only available data points are the planets and moons in our own solar system.

Conclusion

Well I wrote a lot there, and hopefully it is all comprehensible. All in all, there are some interesting bits to Nikolov and Zeller's approach, but I think they are over simplifying some things and are using a non-physical science applicable methodology to obtain questionable conclusions.

Honestly, I don't think that anyone should be treating their research pejoratively (I'm looking at you Andrew Jon Dodds in the comments). It is interesting, and it is certainly novel (from everything I've read). It just doesn't have great conclusions. And that's fine! Most research probably doesn't lead anywhere useful. At least they tried something. People seem to be mad at them just because the results are contrary to the general climate change consensus. Research should be appraised on its merits (or lack thereof) and not on whether its conclusions match preconceptions.


Are we consuming more oxygen than the world is producing due to fossil fuels? With the disclaimer than I am not a scientist, my understanding is that the earth developed a surplus of atmospheric oxygen over the eons because a small percentage of photosynthetic organisms were fossilized instead of decomposing (therefore releasing a net production of oxygen). The oxygen produced by forests is a zero gain, since the forests consume their own oxygen through forest fires and decomposition.  When we burn fossil fuels, we lose these net oxygen molecules. Does that imply that the world is at risk of running out of atmospheric oxygen? Aside for other environmental concerns, can the continued use of fossil fuels create an oxygen crisis?
Put in other words, do the oceans produce enough oxygen to account for our current use of fossil fuels and population growth?

Yes, atmospheric oxygen is being depleted by fossil fuel burning.
From https://cdiac.ess-dive.lbl.gov/trends/oxygen/modern_records.html -

Oxygen concentrations are currently declining at roughly 19 per meg
per year, or about 4 ppm per year. One "per meg" indicates one
molecule out of 1,000,000 oxygen molecules, or roughly one molecule in
4.8 million molecules of air.

And -

fossil fuel burning is depleting atmospheric oxygen at a rate of almost 1000 tons per second. There are about 32 million seconds in a
year, so that somewhere around 30 billion tons of O2 are being
converted to CO2 annually.

Because the quantities of O2 are very large the reduction is small in comparison. From same source -

There are about 1,200,000 billion metric tons of O2 in the atmosphere,
so we can keep burning fossil fuels at the present rate for 40,000
years before we run out of oxygen. By then, all of the world's fossil
fuel supply will have long since been exhausted.


Stop earth rotation around its axis I have a theoretical question. I have been reading on what would happen if the earth suddenly stopped rotating around its axis, and I have learned that would result in the annihilation of all life on the planet. I also learned that the earth rotates currently at 465 meters/second.

Now, my question. What is the optimal deceleration factor that would allow the earth to stop over time (and not suddenly), while allowing live to continue? How do I build a machine to slow down the earth to a complete stop, without destroying all life on planet?

Thanks.

Slowing the planet would have major consequences. Stopping the planet would have major consequences (here are some: Effect on sea level if the Earth stopped rotating).

Doing either of these things too quickly would have even greater consequences, but trying to predict these consequences and the effects for life on earth would be (a) a major primary research project, and (b) perhaps impossible. The answer is that we just don't know, and I doubt that anybody is about to fund the research ;-)

How to do it is, as I suspect you realise, also a very big question. I mean, if for some reason you wanted to. The difficulty is conservation of angular momentum: for the planet to have stopped turning, you need to have shifted that angular momentum somewhere else. That probably means firing stuff into space, or using tidal mechanisms (as somebody noted re the Moon), or maybe building a giant / massive flywheel on the Earth's axis and spinning it really fast the other way..... all of these are, of course, well into the realm of science fiction.


Removing agricultural plastic film waste after 10+ years degradation I am at a farm where previous tenants left a non-biodegradable plastic film roughly 10-15 years ago.  It is inconsistently spread over a few acres and was not discovered until we attempted plowing the fields.  The fields are overgrown with weeds (grasses, thistles, small shrubs, etc.) about 1m tall and this growth has fragmented the plastic considerably (see image, left).
The plastic must be removed in order for food to be safely grown there, and to meet the organic standards of the farm.

What method and equipment (such as an excavator) would best remove the plastic and top layers of soil, with minimal damage to the remaining soil (ie minimal degradation)?

One issue that you've got is the area will be contaminated with fragments of plastic that are microscopic in size to large pieces and they will be at varying depths throughout the soil.

To most people that wouldn't be much of a problem, but for you, who wants to grow food with an organic certification it's going to be a major problem.

Setting fire to that land and burning the plastic with dried vegetation is not a option for you and your desired organic accreditation.

If you can't use the land for another purpose, such a site for new buildings, a parking lot for visitors, or a new roadway you may need to dig deeply to remove the affected soil, and more, and then import replacement soil from elsewhere.


Importance of meteorite impact craters in geology? What is the economic importance of large meteorite impact craters with a diameter over 100 m? Can they form diamonds or produce other economic deposits?

Impact diamonds

Yes, diamonds can form in meteorite impacts. For this several things need to happen:

A meteorite of the correct size and velocity,
The stuff it hits needs to contain carbon.

If you have a meteorite hitting granite or ocean you're not going to get any diamonds. It usually has to hit something that has biogenic carbon (let's say peat, coal, graphite). Even then, the diamonds will form only in a very specific distance from ground zero, because there is a specific relation between pressure and temperature that has to hold. Pressure has to be high enough to stabilise diamonds, it has to be hot enough to break the graphite carbon bonds, but not too hot to destabilise diamond. This is why it also depends on the size and velocity of the meteorite - only some will make these unique conditions happen. A notable case is the Popigai crater in Russia (that has some weird stuff in it). Another case is the stuff found in the peat around the Tunguska event.

However, calling the material that forms "diamond" does not say much about what it's actually like. In some cases, it's not even proper diamond, but rather a carbon polymorph called lonsdaleite, which is some kind of "hexagonal diamond" which has lower hardness than real diamond. Impact diamonds are also usually not pretty, so they're not suitable as gemstones in jewelry. If anything, they're useful as industrial diamonds. The thing is, that making industrial diamonds synthetically is much easier than digging them up from these locations. So, the answer is no. The economical significance of meteorite impact craters in relation to diamond formation is negligible.

Pretty diamonds usually form in Earth's mantle and are brought up to the surface in volcanic eruptions. They are mined from volcanic pipes such as kimberlites, and even though some of them are named like they're impact craters (like the Crater of Diamonds State Park) they are not actually impact craters.

Other stuff

There is one notable occurrence of an impact crater that did cause economic mineralisation of something: the Sudbury Igneous Complex, or the Sudbury Basic, in Canada. In here, a meteorite impact caused melting of the crust and the formation of a nickel deposit. Currently, nickel, copper and some noble metals are mined from there. Even though it has been known for more than 100 years, only in the past 30 years or so the impact origin of it has been fully accepted.


Difference between soil Water Holding Capacity and soil pore volume? I have got confused

I took 100g soil in a funnel with filter paper. poured 100 ml water and collected the drained water in a calibrated cylinder.

Water added in funnel = 100 ml
Water collected in cylinder = 39 ml.
Water retained by soil = 61ml.
Thus soil WHC = 61ml/100g soil

Is this same as Soil Pore volume? If not how should I calculate soil pore volume by water volume method?

As Friddy says, if it's not constrained and relatively intact you're going to have issues with pore volume calculations. Generally the saturate-and-dry method, using a soil core, will give you both the water mass and the mass of sediment. Then you'd use the average density of soil (which will depend somewhat on the minerology, and if it's got lots of organic matter--which can be calculated by burning off OM in a 400 C oven) to get at the particle volume. The known volume of the core minus the estimated particle volume would give you the pore volume.

Googling bulk density and particle density should find lots of info on how exactly to do this calculation.


Zeolites, odor control, and the witchcraft of sunlight Various companies offer "volcanic crystals" or "volcanic rock" available in small mesh bags for odor control.  The best description I have found is that these are made up largely of Zeolites.  All of these manufacturers suggest that the rocks will trap odors and to just recharge the rocks every 6 months by putting it out in direct sunlight.

This sounds like witchcraft!  Can someone explain why putting the rocks in sunlight (versus other light) recharges them and makes them effective at trapping odors again?  How does the light "release" the odor?  Is it the heat of the sunlight, or could this be used in the winter as well?

Zeolites are very similar to clays, with one key difference. The molecular structure of clays is rather compact. In contrast, the molecular structure of zeolites has tiny molecular-sized holes, and these holes are wont to connect. The result is a porous, tunnel-filled structure at the molecular level.

The resulting tunnels make zeolites very good at absorbing substances that fit very nicely in those tunnels. What those substances are depends on the zeolite. There are a large number of naturally occurring zeolites, and even larger number of manufactured zeolites. Which zeolite absorbs what substance depends very much on the nature of the holes in the zeolite. As an example, the International Space Station uses a particular kind of zeolites ("zeolite 5A") to selectively absorb carbon dioxide from the breathing atmosphere.

Zeolites would need to be discarded after becoming saturated if all they did was absorb stuff. That's not the case. It's rather easy to make zeolites relinquish the stuff they have absorbed because the absorption mechanism is rather weak. All it takes is a smallish amount of energy. Zeolites used in industrial settings are subjected to heat, noxious chemicals,or both to make them relinquish the stuff they have absorbed.

In addition to having a large number of industrial uses, zeolites have apparently become attractive to the "all natural" crowd. (I suspect the larger number of "non-natural" zeolites are verboten amongst this crowd.) Exposing zeolites to sunlight means they absorb heat and ultraviolet light. This is indeed one way to make zeolites reject whatever has been absorbed. That's not very efficient; it would be much more efficient to bake those zeolites and/or expose them to a series of caustic chemical baths. However, that wouldn't play well with the "all natural" crowd.


What are the distinguishing features of an "artificial seismic wave" (e.g. a large underground explosion) IN the NPR news item North Korea Possibly Conducts Sixth Nuclear Test, South Korea Says:

The U.S. Geological Survey says it detected a 6.3 magnitude "possible explosion" near Sungjibaegam, North Korea Sunday afternoon, "located near the site where North Korea has detonated nuclear explosions in the past."
South Korean Joint Chiefs of Staff say they detected an "artificial seismic wave" at 12:29 p.m. local time and are "currently looking into the possibility of it being a nuclear test."
The incident was near North Korea's Punggye-ri nuclear test site, which is in the country's northeast and the site of the five previous tests.

The magnitude and location of the event are strongly suggestive of the cause, but if the location were very different, it sounds like the nature of the seismic waves would already indicate that the source was artificial rather than a natural geological seismic event.
Question: What is it about a seismic wave measurements that would allow one to distinguish between natural geological and artificial causes?

below: "North Korea has conducted six nuclear tests. As this chart of seismic activity shows, the latest test on Sept. 3 was roughly an order of magnitude larger than earlier ones." From the NPR new item Here's How Big North Korea's Latest Nuclear Test Actually Was, Original: CTBTO

Several things can indicate that a seismic event is an explosion and not an earthquake.

Firstly, the depth of the source. The shallowest earthquakes tend to have a hypocentre that is at least a couple of km below the ground surface and some earthquakes in certain parts of the world can go down to about 700 km. Artificial explosions on the other hand, will be very shallow, with a hypocentre that is essentially at the surface.

Secondly, and more importantly, the P-wave radiation pattern (and S-wave as well) for an explosion is fundamentally different to that of an earthquake. This can be investigated by plotting the polarities of the first arriving waves of a seismic event on a stereonet, with the position on the net being determined by the azimuth of the source from the receiving station and the outgoing angle of the wave from the source.

Earthquakes radiate P-waves in four lobes, with alternating polarities. This is called a double couple source and it produces a fault plane solution with two positive and two negative quadrants.

An explosion, radiates P-waves equally in all directions and so produces an isotropic pattern.

You may have seen reports of a second seismic event after the nuclear test which has been interpreted as a tunnel collapse. This also has a distinctive focal mechanism, called a compensated linear vector dipole (CLVD).

The photo shows directions of first motion at the source (a) (outwards = positive, inwards = negative), the P-wave radiation pattern (b), the steroplot of each focal mechanism (c).

These links give some further introduction to how stereonets are used to analyse earthquakes:

https://ocw.mit.edu/courses/earth-atmospheric-and-planetary-sciences/12-510-introduction-to-seismology-spring-2010/lecture-notes/lec18.pdf

http://www.ucl.ac.uk/EarthSci/people/lidunka/GEOL2014/Geophysics4%20-%20Seismic%20waves/Seismology/Earthquake%20Seismology2.htm

http://rses.anu.edu.au/~nick/teachdoc/lecture11.pdf


Why are pole reversals not more detrimental to life? This question is linked to the following question, and has two parts.

Mars interdicts approximately 40% of the radiation (per square meter) of the sun that Earth does. It has been claimed that Mars is unsustainable to human life, in part due to the particle radiation from the solar wind, such that a four year round trip to Mars is likely to cause cancer and/or permanent damage to the genome etc.  Why does a pole reversal, which typically takes 1000 years, not have a period of radiation that is intolerable to life?
Not only do migratory birds require the magnetic pole for direction, certain bacteria/algae do to rise and fall in the oceans correctly.  If the pole reversal is not very quick, why do bird migrations not go askew in major numbers. (P.S. I am a little skeptical of the learned landscape proposal found in the linked question - is there evidence for a similar lateral paths taken by birds, year on year, to prove they are recognizing landscapes? Landscapes and features change very quickly over distance. And if so, does the magnetic direction sense really help the migration? Also, when it does reverse, if magnetic field is a key component to knowing direction, then won't that tend to drive them in the opposite direction, so even a quick final phase of a reversal may result in a large number of missing birds.)  Also, why doesn't the food chain collapse when microbial creatures start to dive deeper when they used to head to the surface as a result of their magnetic compass?

There are several factors to consider. The main one is the atmosphere (especially if you want to compare Mars with the Earth's during magnetic reversals). Earth's atmosphere is a formidable shield against solar wind and cosmic radiation. Each type of radiation have a different penetration, but in general the radiation dose associated to each type of radiation decays exponentially at lower elevations. For example for ionizing radiation the relationship is

$E(z)=E_0 \left(0.21 e^{-1.649 z} + 0.79 e^{-0.4528 z}\right)$

Where $E$ is the dose, $E_0$ is the dose ate sea level and z is the altitude (reference). The following figure illustrate how the radiation dose drop at lower elevations. But if you extend that curve to 100 km you will be able to grasp how much of the incoming radiation is filtered by the atmosphere.

Figure: Cosmic radiation exposure as a function of altitude, latitude 50° north, taken from the European Nuclear Society.

Therefore even in the absence of magnetic field, only a small fraction of the radiation would make it to the surface. And note that reversals only means a weakening of the magnetic field, not a complete disappearance. What can disappear is the dipole component of the magnetic field, not the magnetic field as a whole.

It is important to note also that the magnetic field is very important to prevent atmospheric erosion. Therefore, a permanent lack of magnetic field can generate the loss of the atmosphere (likely what happened to Mars). Conversely, Earth's magnetic field is one of the reasons we have a very thick atmosphere compared to Mars, and during the brief periods of magnetic field weakening (due to pole reversals), our thick atmosphere still provided a quite effective protection.

The fact that space radiation doesn't penetrate much can be observed in many different ways, one of them is noting that auroras (a.k.a. northern lights) usually never happen below 90 km of elevation.

Moreover, the reason why auroras happen only at high latitudes (i.e. near the poles), is due to the "geomagnetic latitude effect" that describe how radiations dose rates are minimal at the equator and maximal at the geomagnetic poles. Nevertheless, the atmosphere absorbs most of that extra radiation and life thrives in the arctic forest without any problems.

Also, the atmosphere would not be just a passive filter, it could create its own magnetic field as some studies suggest. Such studies argue that as long as we have atmosphere, the solar wind can induced a magnetic field around the Earth even in the absence of internal magnetic field (reference)

The other important point is: Would the paleontologic record of migratory birds populations and magnetic-dependant microbial life be good enough to detect a catastrophic population reduction on migratory birds and some microbial life that happened 780,000 years ago? I'm not an expert but I would be skeptical. In fact, 780,000 years seems to be enough time for the evolution whole new species and the rise of the migratory behaviour from scratch. More recent reversal events like the Laschamp event 41,000 years ago were much quicker than 1,000 years, and even so, I wonder how well we could reconstruct migratory birds populations that far back (considering that we have trouble reconstructing human populations back then).

Regarding migratory birds, you say that after the reversal the birds would migrate in the wrong direction. And that is quite questionable. In the lack of any point of reference, using an improvised compass to know the north-south direction is easy, but figuring out which side is north and which is south is much more difficult. Therefore, maybe birds use other means to figure that out which side of their compasses is north, means that don't depend on the magnetic field. For example, the side at which sunrise happen or something like that.

Finally, microbes evolve and adapt very quickly, so even assuming that some (or many) of them would die during reversals, I'm sure others would take their place. At the end the ocean microbiota is nutrient-limited, and all the nutrients not used by the dying species will be used by other species that can thrive with a weaker magnetic field. So I wouldn't be so quick to think that such event would lead to a food chain collapse.


What causes such a narrow slit in a cliff? (see photo) I have this photo as a background image and I often wonder how such a narrow, well-defined slit could be formed. Is it natural or man-made? If natural, what processes could have formed it? The rest of the coastline is rugged but this appears very uniform. It is on the north-west coast of Jersey (UK).

If you see the other user (Jan Doggen's) google maps link, you can see apparently similar features in different states - this is a particularly neat example of a general phenomenon.

These notches form when headlands are undercut by caves carved out by the sea. They may be initiated where there is a fault or jointing in the rock (northwest Jersey is granite, according to google).

In this particular case, the notch seems to have a rounded termination. Blowholes also form from undercutting of headlands producing caves whose roofs then collapse. It's possible this cave may have collapsed after a blowhole formed, so you get a notch where the inland end of the feature appears rounded. That bit is just speculation though.

I found this Jersey geology trail guide that might have more detail: http://jerseygeologytrail.net/Geomorph.shtml


How does palingenetic fusion occur in rock? As far as charnockites are concerned, granitic charnockites are formed due to palingenetic fusion and metasomatism, while granulitic charnockites are formed due to high grade metamorphism.

When I googled for palingenetic fusion, I haven't gotten any clear vision.

Can anyone help me to grab the answer for my question?

I have never seen the term "palingenetic fusion" anywhere in the geological literature, but seeing that it means:

  Palingenesis is a concept of rebirth or re-creation, used in various contexts in philosophy, theology, politics, and biology. Its meaning stems from Greek palin, meaning again, and genesis, meaning birth.

And seeing that it is used to describe granitic charnockites, I think it is safe to say it is a very obscure term for anatexis, a common process of granite formation by partial melting of pre-existing rock. This is most commonly used in high grade metamorphic rocks, and in the context of formation of migmatites and leucogranites.


Underwater rock conduit After looking at this question - Source of water for the Great Artesian Basin in Australia one would like to know whether there are any underwater rock conduits that transport fresh water across seas in the world. I have not come across any in my search, but maybe there does exist that I am not aware of.

I must admit that I was not well informed on the matter of offshore aquifers before reading this thread. Usually when I think about the hydrologic models I think of the water as a dynamic component of a system (snow, streams, moisture, glaciers) and not necessarily old water pockets somewhat trapped deep (and at the moment with no know perceptible input/ouput in the system). In line with those classical hydrologic cycle model.

I searched a bit and found this paper on physorg.org which led me to other reads on the matter.

Apparently there is substantial offshore freshwater aquifers, trapped undersea. Water from Pleistocene, which probably got trapped during the glaciations, while the mean sea level was much lower. When the ice sheet (ex: Laurentidian) receded, sea level rose and freshwater in charged aquifers would be somewhat trapped and sealed. Multiple glaciation during the Pleistocene would have enabled the process to cycle multiple time during the last 2.5 M year.

And yes - the related paper in Nature specify that some of those 30 inventoried undersea aquifers have an onshore connection (Perth among others is listed there).

This is pretty interesting but in my opinion there is not a ton of paper on the question. Yet I will keep this part of this (paleo!) hydrologic cycle in mind when such questions and discussions arise in the future.


Can Venus be considered to be tectonically active? Venus is noted for its absence of spreading ridges, transform faults, and subduction zones, which are characteristic of plate tectonics on Earth. But given that it exhibits rift zones, mountain belts and other "secondary" features of tectonic activity, should it be considered tectonically active?

There has been some considerable modelling about this particular scientific issue, as it is considered important to understand Venusian tectonics to be able to get a better understanding of Earth tectonics (1).

So, in answer to your question, is Venus tectonically active, the answer from current research suggests that it is not - but not at the moment, especially not like Earth. Much of the research refers to Venus as currently possessing a "stagnant-lid" single plate (1),(2), (5).  The tectonic-like features found on Venus have not been observed to 'fit' a global pattern that would suggest a 'mobile-lid' tectonic regime like that of Earth (1). Much of the recent research has not really focused much on the differences between Earth and Venus - including, the Moon, liquid water and differences in rotation, but rather focuses on what observations of orbiting spacecraft, such as Magellan and the Venus Explorer have revealed and what models based on these have deduced.

Recent research has painted a picture that the answer to this question is considerably more complex than would justify a 'yes' or 'no' answer.

Modelling from gravity and topographic anomalies observed by several of the space craft that we have sent to Venus suggest that many of these features are derived from 'hotspot' upwelling mantle plumes where partial melting could occur (2).  This is supported by an example of a recent re-evaluation of earlier observations of tectonic-like features on Venus was performed by McGovern et al. (2014) (3) of Magellan images, using stereo radargrammatic images, of the graben-like structures that extend from the Venusian shield volcanoes reveal that they, alongside the radial dike emplacements, are accounted for by magma reservoir expansion (1).

Models reported by Huang et al. 2014 (2) also suggest that Venus has a very thick lithosphere compared to that of Earth, which would support the high topography noted for Venus (5).  Related to this is that in deformation experiments, Azuma et al. 2014 (4) suggest that is a mechanical decoupling of the Venusian crust and the mantle convection (as shown in the diagram below (4)).  Huang et al. (2) models also have found that Venus cannot have a weak asthenosphere in the way that Earth does.

So, coming back to what I meant about not being tectonically active 'at the moment' in the first paragraph.  This comes from the observation that the entire planet seems to have been resurfaced approximately 750 million years ago, evidenced through the amount of craters and other features (1).  This has lead to some researchers, such as Turcotte, 1993 (5) to suggest that tectonic activity on Venus is episodic. The process is hypothesised by Head, 2014 (1) as comprising 3 stages:

A relatively short phase of intense tectonism, as indicated by the tesserae, high plateaus, plains deformation and coronae - Turcotte (5) theorises that the formation of coronae could be an indication of a new episode of tectonism.
A relatively short phase of intense volcanism, with minor subsidence and deformation.
A long period of network rifting (graben formation, modelled to be hotspot induced (3)) and volcanism.

Recent modelling by Gillman and Tackley (2014) (6) provide a possible mechanism to the 3 stage process by Head, 2014 (1).  Gillman and Tackley's models suggest that the thick Venusian atmospheric surface temperature provides a boundary layer for mantle convection models, in particular, the atmospheric water vapor pressure which is sensitive to volcanic activity.  They suggest that cooler surface temperatures result in a 'mobile-lid' type of tectonic regime, that is until the temperature rises again causing a return to the stagnant-lid one plate scenario that we observe today.

References

(1) Head, 2014, The geologic evolution of Venus: Insights into Earth history Geology

(2) Huang et al. 2013, Constraints of the topography, gravity and volcanism on Venusian mantle
dynamics and generation of plate tectonics, Earth and Planetary Science Letters

(3) McGovern et al. 2014, New constraints on volcano-tectonic evolution of large volcanic edifices on Venus from stereo topography–derived strain estimates Geology

(4) Azuma et al. 2014, Rheological decoupling at the Moho and implication to Venusian tectonics, Nature

(5) Turcotte, 1993, An episodic hypothesis for Venusian tectonics, Journal of Geophysical Rsearch

(6) Gillman and Tackley, 2014, Atmosphere/mantle coupling and feedbacks on Venus, Journal of Geophysical Research


What part of a hurricane determines if it makes landfall? Watching the news for the US hurricane Harvey and they say it will make landfall soon. But what part of the hurricane are they referring to?

Hurricanes make "landfall" when the center of the eye moves over land.

From the NOAA National Hurricane Center glossary:

  Landfall:
  The intersection of the surface center of a tropical cyclone with a coastline.Because the strongest winds in a tropical cyclone are not located precisely at the center, it is possible for a cyclone's strongest winds to be experienced over land even if landfall does not occur. Similarly, it is possible for a tropical cyclone to make landfall and have its strongest winds remain over the water.

Below is an example image showing when landfall occurred for Hurricane Harvey:


Why is the upper atmosphere brighter than the lower atmosphere in some photos from space? In most photos from space, the atmosphere gradually fades away from pretty bright blue to essentially black, as you move away from the Earth surface, such as can be seen in this photo of the Earth from the ISS (also showing some noctilucent clouds):

NASA photo of Earth atmosphere.  Source: NASA

Or by night (again with noctilucent clouds):

Earth atmosphere by night.  Source: NASA

Yet in photos with an exposure long enough for stars and airglow to be clearly visible, the opposite appears to be the case:

NASA photo of Earth atmosphere and milky way.  Source: NASA

In the third photo, the Earth is rather dark.  Moving away from the Earth, the sky closest to the Earth is colourful, but faint enough for stars to be visible through it.  Then the atmosphere appears to get brighter as you move further up, until it becomes abruptly black after a sharp edge.  Higher up still we can see a faint but clearly visible band of red airglow.  It's not aurora — aurora is higher up than airglow, and not so constant.

Another example, but with different colours (that could be a side-effect of exposure or editing):

ESA starry night.  Source: ESA via Wikimedia Commons

The glow observed in those pictures in the upper layers of the atmosphere is the airglow from OH molecules. OH emission peaks between 75 and 105 km of elevation (Blamont and Reed, 1967) with intensities peaking at different wavelengths, the most prominent peaks in the visible spectrum are 557nm (Green), and multiple other peaks between 620 and 750 nm (red)

In 1965 the OGO-II satellite was launched with the propose to measure airglow, the following image show a typical altitude vs intensity profile:

From Blamont and Reed, (1967). The peak around 100 km is mostly due to OH airglow and the broader peak around 250 km is mostly due to atomic oxigen.

Regarding the color observed in the pictures, while it is difficult to trust them due to photo editing, they are consisten with OH airglow, in the greens, yellows and reds. This is the airglow spectrum from Broadfoot  and Kendall (1968), where I've highlighted in yellow the most important emission bands of OH in the visible range:

To get a sense of the color associated to each band here is a approximate scale (remember 1 nm = 10 Å)

From wikipedia

The fading yellow glow that goes below the brightest band can be explained as the OH glow at the same altitude band (75-105 km) but originating from the part of the atmosphere that is closer (or further) to the spacecraft from which the picture was taken. As that altitude band is a shell around the Earth and not a ring. For the same reason the peak intensity in the picture is likely a bit lower than altitude of the peak in emissions.


Is there a buildup of static electricity in a sandstorm? In a sandstorm, is there a buildup of static electricity? If so, does that produce lightning strikes? Also if you were to be inside the storm what would the build of that level of static feel like?

Sandstorms occur in dry areas, particularly deserts. The sand particles are fairly uniform in size. As the dry sand moves due to the wind it begins a leaping process known as saltation. Quoting the Wikipedia article:

  the initial saltation of sand particles induces a static electric field by friction

The sand particles become polarized and as the particles begin to hit each other the polarization on each grain gets rearranged and the degree of polarization doubles with each interaction. With a build up of static electric charge lightning can develop.

The greatest build up of static charge occurs in sandstorms of intermediate thickness.


What makes up a gradient My question is a two part question. First I currently know of two different gradients.I think there is more; however, I don't completely understand what makes a gradient. So, here is my questions.

What properties can make up a gradient in atmospheric science?
What atmospheric gradients are there?

Here are the two I knw about.

Pressure gradient
Temperature gradient

Examples would be nice; however, not necessary.

Thanks

In addition to other information others have written in comments, gradients measure the rate of change of "a quantity".

For example, take a hill. As you walk up the hill your elevation increases relative to the base of the hill. The steeper the hill the more quickly your elevation changes. The slope of the hill is defined as the gradient of the hill. The steeper the hill the greater the rate of change of elevation, with respect to the horizontal component of distance traveled.

With atmospheric gradients, imagine there are two towns, each with a weather station. The distance between the two is 100 km.

Each weather station measures pressure & temperature at defined times, usually at half hourly intervals.

If the first town measures a pressure of 1011 hPa and temperature of 25 C @ 10 am and the second town, at 10 am, measures a pressure of 1008 hPa and a temperature of 20 C, then between the two towns there is a pressure gradient of 0.03 hPa/km [(1011-1008)/100]. Likewise there is a temperature gradient of 0.05 C/km [(25-20)/100].

Now, if at 11 am the weather station in the first town records a pressure of 1012.5 hPa and a temperature of 28 C, then over time, there has been a pressure gradient over the first town of 1.5 hPa/h [(1012.5-1011)/1] and a temperature gradient of 3 C/h [(28-25)/1].

So when it comes to gradients, it depends what is being measured (pressure, temperature, humidity) and what is it be measured against (distance, time, etc.), and for atmospheric quantities the distance could be lateral distance or vertical distance.


Does the existence of limestone nodules in a clay soil horizon indicate a limestone bedrock? A profile (clay soil) was excavated to a depth of 100 cm in the north of Tunisia. We have found limestone nodules, colluvium and alluvium. What I would like to know is the nature of the bedrock of this soil. Can we assert that there is a limestone bedrock?

There are three possible sources for the reported limestone nodules from the clay horizon from colluvium and alluvium. First, as noted before, they could be either detrital gravel of limestone either eroded from limestone bedrock. Given that the bedrock source from which this gravel was eroded and transported from could be either local or regional, such gravels tells a person nothing about the composition of the bedrock at your site. Second, the "limestone nodules" might also be limestone gravel that was either brought in either as construction material or eroded and redeposited from larger limestone blocks at some ancient ruin. Again, such gravel could come from any source within either the local area or region. This means that the presence of such material tells a person nothing about of what the local bedrock consists.

Finally, it is interesting that the "limestone nodules" occur in a clay layer. Normally, gravel-size pieces of limestone are not deposited together with clay. This and the clay layer being part of a soil suggest that the limestone nodules" are caliche nodules / concretions that precipitated and formed in place within the soil as part of a Petrocalcic “K” horizon of a soil developed in clayey colluvium and alluvium. Since caliche (calcrete) forms in Quaternary colluvium and alluvium independently of the type of local bedrock, the presence of caliche tells a person nothing about the local bedrock might be. The Soil Map of Tunisia at https://library.wur.nl/isric/kaart/origineel/afr_tnped.jpg might tell a person whether such soils are present within the area. The presence of "limestone nodules" does not indicate what the local bedrock might be composed of as there are multiple possible origins for them that are independent of the underlying bedrock.

A possibly useful map is:

Ben Haj Ali, M., Jedoui, Y., Dali, T., Ben Salem, H. & Memmi, L. (1985): Carte géologique de la Tunisie, echelle 1:500,000.– Office Topographie Cartographie; Tunis

Petrocalcic Horizon - https://en.wikipedia.org/wiki/Petrocalcic_Horizon

caliche / calcrete - https://en.wikipedia.org/wiki/Caliche


What modelling approaches are used to predict the aurora? Are there any resources (books/links) that discuss the mathematical tools and methods used to forecast the aurora borealis activity in a particular location?

I see many websites that claim to predict aurora, but are there any open source code that lets you have an idea of the models?

One model is the OVATION auroral precipitation model.

OVATION stands for Oval  Variation,  Assessment,  Tracking,  Intensity, and  Online  Nowcasting.

The NOAA Space Weather Prediction Center uses the OVATION Prime model for their 30-minute aurora forecast. They use a modified version of the model for their 3-day forecast. It was devised by Newell et al. (2010) at Johns Hopkins University.

You can read all about it in Machol et al. (2013). The paper is open access and contains several equations and a description of the method. They explain:

  The OVATION Prime model is derived from electron and proton
  flux measurements from the SSJ4 detectors on the DMSP satellites.

SSJ4 sensors, according to one source:

  [...consist] of an array of four cylindrical, curved plate, electrostatic analyzers configured into two pairs; one pair each to measure electrons and ions. Each pair covers the energy range from 30 eV to 30 keV in 20 channels spaced at equal intervals in energy on a logarithmic scale.

References

Machol, J. L., J. C. Green, R. J. Redmon, R. A. Viereck, and P. T. Newell (2012), Evaluation of OVATION Prime as a forecast model for visible aurorae, Space Weather, 10, S03005, doi:10.1029/2011SW000746.

Newell, P. T., T. Sotirelis, and S. Wing (2010a), Seasonal variations in diffuse, monoenergetic, and broadband aurora, J. Geophys. Res., 115, A03216, doi:10.1029/2009JA014805.


Is there a list of instances where mountains that have been mined out of existence? Reading the Wikipedia entry for the Australian town of Broken Hill, I came across the following piece of trivia (emphasis mine):

  The "broken hill" that gave its name to Broken Hill actually comprised a number of hills that appeared to have a break in them. The broken hill no longer exists, having been mined away.

Surely there must be many other examples of this happening over the course of human history? I haven't been able to find any.

Is there a term for mountains or hills that have been wiped out of existence due to mining or some other human activity? Or perhaps a list of such instances?

Of course it happens elsewhere! However, I'm not sure there's a specific term, generally. Even in the "montaintop removal" country of Appalachia, there is no more prosaic term for the practice other than MTR. Too bad! It surely deserves a better term!

And...despite the complete excising of an entire mountain within the Oquirh mountains, even the Salt Lake City population has no term for Complete Mountain Removal!


What Makes Round Holes In Superior Agates? I found this rock in Western Wisconsin. Pretty sure it's a Lake Superior Agate?

Wondering what would make the white eye that has red in its center?

Would this rock be a good one to have someone cut in 1/2?

Agate sometimes contains fossils. Your specimen seems to contain a fossil crinoid disc, and probably there are more than one. Crinoids are plant-like animals anchored to the sea bed, and are sometimes called sea lilies. Many species  became extinct millions of years ago, but a few survive today. The stems of ancient crinoids were made up of stacked discs, rather like the one in your agate. When the crinoids died, their stems often disintegrated, and the discs became scattered. The hole you mention is the hole found at the centre of all crinoid discs. For some reason it did not become full of agate, perhaps because there was a gas bubble or some other obstruction in there. I can't predict what you would find if you cut it in half, that decision is entirely up to you. I think it would probably be best to leave it as it is.