Differentiate a rock and mineral How to differentiate between a rock and a mineral by merely looking at it as a thumb rule?

If you see more than one mineral you frequently can call it rock, but not always. You could have a gem incrusted into another mineral or rock.
You need to know each rock uses to have one or more mineral -by definition-, but there are monomineral rocks as limestones, wich can be only composed by calcite.
If you give me a limestone I could say I have a rock, and I see also calcite, normaly with a magnifying glass.
When we are searching for minerals or thinking on minerals, we use to search for well formed species. If you see a big cristal, you can affirm it is a mineral. Sometimes they are twinned. If you see an aggregate of little minerals, most times you have a rock independently if it has one or more mineral types but not all times again.
What characterizes a rock at surface uses to be diagenesis -compaction of minerals- if the rock is sedimentary. Igneous and metamorphic rocks are also well formed mineral aggregates, consistent bodies.
Sedimentary rocks have a lot of minerals/mineraloids cemented by a kind of microcrystaline matrix -that are also minerals crystallographically talking!-.
Igneous and metamorphic rocks are compact bodies were there is a texture, minerals have textural relation (some kind of order).
If you are at an ore, you could be confused again if you don't know basis concepts. You then could think the aggregates of minerals are rocks, wich is not the case. Then you have an aggregate of well formed minerals, wich is not the same as a rock.
There are several definitions of rock and mineral. I took this ones:

Rock:"mineral matter of variable composition, consolidated or
unconsolidated, assembled in masses or considerable quantities in
nature, as by the action of heat or water."
Mineral:"any of a class of substances occurring in nature, usually
comprising inorganic substances, as quartz or feldspar, of definite
chemical composition and usually of definite crystal structure, but
sometimes also including rocks formed by these substances as well as
certain natural products of organic origin, as asphalt or coal."
source: http://www.dictionary.com


Will geothermal cooling be greatly affected by global warming? Geothermal cooling has been an attractive option in the U.S. Northeast
since it emits very little carbon into the atmosphere compared with
compressed refrigerant systems which use lots of electricity.
Geothermal cooling is based on the fact that the ground basically
stays around 50-55 degrees farenheit all year round unless the ground is near
a hot spring or volcanic fault line.
I would think that the temperature of the earth will warm
a little bit which would affect the temperature of the
cooling fluid.

I presume that by geothermal cooling you mean geothermal energy. Yes, it's an attractive option and is used a lot in Iceland, but unfortunately there are not many places that have such easy access to it as Iceland. Geothermal energy will be just one source of non-polluting energy, along with hydro-electricity and many others. Today's global warming is just a passing phase, and will be followed sooner or later by another ice age.

The Earth is gradually cooling as geothermal heat is lost into space and the crust is getting thicker, as has already happened on Mars, but this will have no noticeable effect on Earth for many millions of years, by which time we will have gone to join the dinosaurs.


Why are alpine river water green - blue? I recently visited Slovenia where I saw several rivers with a strong blue-green color.
Here is an example from one of the tributaries of the Soča river near Kobarid. The locals refer to it as an "emerald" color.

Notice how the color gets more intense at the deeper waters. What causes this color? A web search shows that the two most cited reasons are blue-green algae and "limestone particles". I'm guessing that the more plausible explanation in this case is the limestone one, because this area is dominated by limestone. But, is it really "particles"? I would think that the calcium carbonate would dissolve in the water, instead of being suspended as solids.

According to the website Putting the Emerald in Emerald Lake – Where do the colours come from?, the reason for the colour is the same that occurs in lakes, it is due to what is known as or similar material to 'rock flour' - consisting of

  of fine-grained, silt-sized particles of rock, generated by mechanical grinding of bedrock

and relevant to a river environment

  When the sediments enter a river, they turn the river's colour grey, light brown, iridescent blue-green, or milky white.

The colour is due to:

  the suspended material distorts the wavelengths of light, reflecting back more of the green and blue end of the spectrum

These usually originate from glacial melt, even though there are no glaciers in the Julian Alps presently, but there used to be, resulting in according to the WP6 Hydro-geological upgrade and improvement of the GIS of the sources of drinking water webpage as having

  The intergranular aquifer in the alluvium of the Soča/Isonzo River, which is composed of fluvial and fluvioglacial gravel and sand sediments with individual lenses of conglomerates

further explained in the article Bovec basin (Upper Soča valley, Slovenia), as having

  Quaternary
  sediments are represented from bottom to top by partly lithified glaciofluvial sediments, overlain by lacustrine
  chalk. During the Holocene, the chalk was partly eroded (in some areas totally) and covered by glaciofluvial
  sand and gravel which are weakly cemented in some parts into conglomerate and by unconsolidated moraine
  (till).

Potentially, plenty of source material. The particles are small enough to be suspended in the water of the Soča River.


Change in earth mass since the time of the dinosaurs Is there a significant difference in the mass of the Earth between now and the time of the dinosaurs (250 - 75 million years ago)? I was just wondering if the force of gravity on dinosaurs would have been significantly less when they were around.

I gather, but may be wrong, that the mass of earth at present increases by around 108kg/day. All else being equal, one would expect the earth to have gained a mass, since 75 million years ago, of:

$$ 75^6 \times 365 \times 10^8 kg = 6.496 \times 10^{21} kg $$

The current mass of Earth according to Wikipedia is 5.97224kg, so if my math is correct, the change since the time the dinosaurs went extinct would be less than 0.1%.

Is my math correct here? If it is, would the change in the mass of the Earth over this period of time have had any noticeable effect on weight from its gravity?

I gather, but may be wrong, that the mass of earth at present increases by around 108kg/day. All else being equal, one would expect the earth to have gained a mass, since 75 million years ago, of:
$$ 75^6 \times 365 \times 10^8 kg = 6.496 \times 10^{21} kg $$

First off, that should be $75\times10^6$, not $75^6$. That alone makes your estimate high by a factor of 2373. Correcting this error, the mass gain is only $2.7\times10^{18}$ kg, rather than $6.5\times10^{21}$ kg.
Secondly, I've never seen anywhere close to that magnitude of mass gain. The article you cited in a comment gives a range of 5 to 300 metric tons per day. Your value of $10^8$ kilograms per day is 100000 metric tons per day, which is high by at least a factor of 333 (and up to 20000). With this, the mass gain is between $1.5\times10^{14}$ and $8.2\times10^{15}$ kg. This seems big, but it's tiny compared to the mass of the Earth.
Thirdly, you are ignoring atmospheric losses. Almost all of the atmospheric losses are in the form of hydrogen and helium. Most of the lost hydrogen results from water vapor that makes its way from the surface of the Earth into the stratosphere and is dissociated. Most of the lost helium results from radioactive decay in the Earth. Both forms of atmospheric loss represent a decrease in the mass of the Earth. Estimates on this mass loss also vary widely, from 100 to 300 metric tons per day.
Putting these widely varying estimates together means the mass of the Earth is increasing by as much as 200 metric tons per day (+300 mass gain, -100 mass loss), or decreasing by as much as 300 metric tons per day (+5 mass gain, -300 mass loss, and since the numbers vary so widely, that's just -300). Either way, it's small potatoes, even over the course of 75 million years. This means g was between $13\times10^{-9}\,\text{m/s}^2$ smaller than it is now and $9\times10^{-9}\,\text{m/s}^2$ larger than it is now. Both of those numbers are very small.


Greenhouse gas emissions from wildfires in California According to the California Air Resources Board, in 2016 (the most recent year for which figures appear to available) California's total greenhouse gas emissions were 430 million metric tons CO2 equivalent, of which 83% were actual CO2.

In view of a record-breaking string of wildfires in California this year, I am wondering how significant the emission of greenhouse gases from such fires is, but I am having trouble finding relevant data on the internet. What I did find is a chart of daily CO2 emissions during large wildfires earlier this year, which appears to indicate up to an additional 1.5 million metric tons of CO2 emitted per day.

This suggests that in 2018, the total amount of CO2 emitted by wildfires in California might be in the 40 to 50 million metric ton range, or a sizeable portion of California's overall greenhouse gas emissions at around 10 percent. However, this is just a back-of-the-envelope guesstimate (my assumption: 40 to 50 days of major wildfires, at one million metric tons of CO2 equivalent per day), which may be completely flawed.

Are there any reliable (or at minimum, more carefully reasoned) estimates for CO2 emissions from California wildfires, in metric tons per annum? Useful numbers would be estimates for 2018, some other recent year, or for an average year.

The California Air Resources board posted this PDF that includes emission estimates up to 2017, which were 37.1 million metric tons. If anyone is interested in related info, the search phrase I used was, "CO2 estimates for california wildfires".


Why is the Earth's shadow blue? After every sunset, once the sun is gone, I always enjoy seen the belt of venus rising in the other side, followed by the Earth's shadow.

This is a picture I took (you will find better ones online). The Pinkish-purple band on top is the Belt of Venus, and the blue band on the bottom is the Earth's shadow.

This figure from Sky & Telescope explains it well:

While contemplating these beauties, I've had hard time understanding why we see the colors we do. To my eyes, the belt of Venus looks purple, which didn't makes sense to me, as the very short wavelength of purple light should have been scattered long before arriving back there. Then all made sense when I realized that if you mix blue and red light you get purple. So the color comes from the blue mixed with the red light backscattered by the high atmosphere that is still illuminated by the Sun.

However, I can't still figure out why the Earth's shadow looks blue, and I haven't been able to find an answer (here some links about the Earth's shadow but without an explanation of the color: 1, 2, 3).

We know the sky is blue and the sunset red to due the preferential scattering of blue light by the air. But: How can the air in the Earth's shadow scatter blue light if it doesn't get any direct illumination, and any indirect illumination getting back there should be VERY depleted in blue (i.e. mostly red light)?

I thought the fact that the belt of Venus scatters red instead of blue as the rest of the atmosphere, is precisely because back there there is no more blue light left, so the weaker scattering of red light becomes noticeable (please let me know if I'm wrong there).

Or is the air actually emitting blue light in some sort of fluorescence/glowing?

PS: As this is a purely atmospheric phenomena I though it would be better suited here than in the Astronomy SE.

To my eyes, the belt of Venus looks purple, which didn't makes sense to me, as the very short wavelength of purple light should have been scattered long before arriving back there. Then all made sense when I realized that if you mix blue and red light you get purple.

You got that part right. Purple is not violet. Violet is a spectral color at the high frequency end of the visible portion of the spectrum, while purple is a non-spectral color on the line of purples that spans from nearly ultraviolet to nearly infrared. We see color as a wheel rather than as a line. One possible explanation is that the long wavelength ("red") cones have a secondary response in the violet end of the spectrum. Spectral violet light excites both the short wavelength and long wavelength cones, but so does a non-spectral mix of red and blue light.

And that's what you're seeing in the Belt of Venus -- a muted mix of red and blue, or a purple (or perhaps magenta, or a rosy pink).

  So the color comes from the blue mixed with the red light backscattered by the high atmosphere that is still illuminated by the Sun. However, I can't still figure out why the Earth's shadow looks blue.

The backscattered red light doesn't come from the high atmosphere. It comes from the troposphere. The high atmosphere (the stratosphere and above) contains very few particulates. The upper atmosphere is the only part of the atmosphere that remains sunlit above the eastern horizon after sunset. The sunlight hitting the upper atmosphere is Rayleigh scattered, so you see that very faint blue scattered light. You don't see the backscattered reddish light from the particulate-containing lower atmosphere at the eastern horizon because that part of the atmosphere is fully in the Earth's shadow above the eastern horizon.


Are weather changes periodic? (Do the same weather patterns repeat over years?) (Cycles) (Journal paper suggestion) I am wondering if there is long term (10 year, 7 year, 20 year)  periodic patterns Similar to short term seasonal and periodic patterns in weather such as sea/land wind, monsoon, ENSO, ocean sea-saw, etc.

Specifically related to drought
I am trying to predict the rainfall using the weather data, I was wondering if different patterns that happen in weather changes through time are periodic?
Is there a periodic pattern in the pattern of weather changes?
Is there a general periodic pattern that may happen every 10 years or more? If so, how long is the window of this period?
Or a similar question can be: the weather measurements of how far ago can affect today's weather measurements?
Does the weather forget about the weather events of long time ago? If so, how long is that window?
If there is a journal paper or material that I can study please tell me. Thanks
Additional Explanation:
I am a data scientist trying to predict rainfall using weather data. So I do not have earth science knowledge. So after I read @Fred's comment, I understood that what I have in mind is called 'Cycle' in earth sciences.

edited question: What is the length of the cycles for rainfall patterns? (If I want to predict rainfall, how long is the length for cycles that affect rainfall? Or how many years of data I should use?! )

I'll address this part of the question first:
"Or a similar question can be: the weather measurements of how far ago can affect today's weather measurements? Does the weather forget about the weather events of long time ago? If so, how long is that window?"
The answer is "approximately two weeks". Even with nearly perfect knowledge of the atmospheric state (the distribution of pressure, moisture, aerosols, etc), the chaotic nature of fluids means that beyond two weeks, one would be better of predicting the weather from a climatological estimate (i.e, the average of the weather on that date for the last ~30 years). Research into this very question was foundational for the field of Chaos theory (Lorenz, 1963 is a famous example). This isn't just an artifact of the predictive models, but the natural system itself. The weather has effectively 'forgotten' what it was doing a few weeks before.
While the atmosphere has a short 'memory', other parts of the Earth have longer 'memories'. Notable examples are the Oceans and the Landsurface. A warm anomaly in the Ocean will stick around for a while, since ocean currents are much slower than air for mixing things around (and diffusing out the anomaly). The atmosphere is very influenced by what happens on the surface, so the warm/cool anomaly can affects the weather in various ways. This is what happens in the case of ENSO that you have mentioned. The land can also have an impact. The amount of saturation in the soil can have quite a big impact on weather, especially for things like thunderstorms and monsoon systems. Continental snow cover extent may also impact atmospheric predictability. Stratosphere/troposphere coupling mechanisms might also be a source of longer term predictability.
And this part:
"I am wondering if there is long term (10 year, 7 year, 20 year) periodic patterns Similar to short term seasonal and periodic patterns in weather such as sea/land wind, monsoon, ENSO, ocean sea-saw, etc."
The most well known ~10 year climate oscillation is the Pacific Decadal Oscillation.


What causes the "ripples" that extend east-west along the mid-atlantic ridge? Below are two cropped screenshots from the super-cool video Draining Earth's oceans, revealing the two-thirds of Earth's surface we don't get to see with the oceans "drained" to 4000 and 5000 meters below sea level.

We've all read about the magnetic field reversals leaving alternating lines of residual magnetic field trapped in the crust that go in the north-south direction, but I was surprised to see these topographic ripples that extend in the east-west direction.

What caused these to form?

I've added some annotation to indicate the direction of the ripples I think I'm seeing.

These are transform faults that result from differential spreading rates of the middle ocean ridge. As such they are part of the plate boundary. Possible causes are different production rates of magma, thermal differences of the sea floor, differences of relative plate movement.

https://en.wikipedia.org/wiki/Transform_fault

https://en.wikipedia.org/wiki/Mid-ocean_ridge

Paywalled:
Dynamical Instability Produces Transform Faults at Mid-Ocean Ridges

And:
Wilson, 1965: A New Class of Faults and their Bearing on Continental Drift

Inactive transform faults extending beyond the spreading zone are sometimes generally named "fracture zone".

But transform faults can also reach all the way to the next subduction zone (e.g. Azores-Gibraltar fault zone) and be responsible for devastating earthquakes.


Why does New Zealand and cold countries have volcanoes? I understand that volcanoes are caused by the heat that causes high intense pressure below the Earth's surface. This intense pressure gets released and causes magna which becomes hot lava to flow out from inside the Earth.

Why does it happen in New Zealand or any cold countries? There is no way that the Earth will be over-heated there.

Surface temperatures on Earth are a consequence of solar heating and radiative cooling - in other words, the heat energy which drives climate comes from sunlight falling on the Earth "now".

On the other hand, the heat energy driving volcanism is left over from the formation of the Earth (4.5 billion years ago), stored deep inside the planet, with some additional heat generated from the radioactive decay of elements contained in the rocks.

Deep within the Earth, the temperature is on the order of 5000-7000 K. It's obviously much cooler at the surface. The high temperatures cause the rock and metal of which the Earth is composed to melt. The temperature gradient results in a slight density gradient, which drives convection (flow of hot material up to the surface). When that hot material breaks through the surface, you have a volcano.

Consider that the hottest places on Earth (in terms of climate) don't have surface temperatures anywhere close to what it takes to melt rock (maybe 50 °C compared to 1000s of °C). Heat can only move from where the temperature is higher to where it is lower. Less heat falls on the planet from the Sun than the Earth radiates away into space; that difference is heat finding its way up to the surface from within. So, the heat driving volcanoes cannot possibly be coming from sunlight striking the Earth; it can only come from heat stored inside the planet from long ago. Consider also that the difference in temperature between the hottest places on the Earth and the coldest (in terms of climate) differ by little more than 100 °C. That's a tiny fraction of the temperature difference between molten magma and even the hottest desert. Bottom line: climate has no effect on volcanic activity.

Since the Earth is losing more heat to space than is falling on it from the Sun, and that heat is coming up from below, the core is gradually cooling. But there is so much heat inside the Earth and the rate is so slow that our Sun will die before Earth's core cools enough to solidify.


What is "qflux" and why is it important for climate models? Evaluation of the Ocean Q Flux is an example of qflux used in the CESM model.

Why is it important?

Q= Ocean heat flux

Slab Ocean Model is the name when the atmospheric component of CESM is coupled with ocean mixed layer. When CESM is configured in the fully coupled way, there's no need for the Q flux computation.

GCMs coupled with ocean mixed layer (and thus a thermodynamical ocean instead of a dynamical ocean) computes Q flux to account for the exchange of heat with the ocean.

See http://www.cesm.ucar.edu/models/atm-cam/docs/description/node28.html:

  The ocean mixed layer contains an internal heat source $ Q$ (also called a $ Q$ flux), whose values are generally specified by a CAM control run, representing seasonal deep water exchange and horizontal ocean heat transport. For example, using prescribed sea surface temperatures and sea ice distributions, the net surface energy flux over the ocean surface can be evaluated to yield the heat source $ Q$.


Looking for counter-arguments concerning the melting of glaciers in the alps in the context of global warming I've recently listend to a talk of Prof. Gernot Patzelt, Austrian Geographer and High Altitude Mountain Researcher. In this talk he describes that scientists find rests of trees and moorland apearing under the melting ice in the alps (Source: https://www.eike-klima-energie.eu/tag/patzelt/?print=print-search). He concludes that it must have been much warmer in times when mankind was not yet able to bring CO2 in the atmosphere and there is no causal relationship between the melting of the glaciers in the alps and the amount of CO2 in the atmosphere.

These arguments are used by a lot climate-change-sceptics. This is why I'm looking for counter-arguments for this line of argument. As far as I can see melting glaciers can be one indication for a regional or global warming, no matter what's the reason for that warming. So I guess he mixes up indications for a warming with the proof of causality (CO2 -> global warming)? Correct? Any other ideas?

Martina

He concludes that it must have been much warmer in times when mankind was not yet able to bring CO2 in the atmosphere and there is no causal relationship between the melting of the glaciers in the alps and the amount of CO2 in the atmosphere.

This incorrectly collapses several things.

Mankind is not the only cause of CO2 in the atmosphere. There have been warmer periods caused by CO2, but it was not man-made.
I think you slightly misrepresented his words by quoting no causal relationship between the melting of the glaciers in the alps and the amount of CO2 in the atmosphere, but actually meaning is no causal relationship between the melting of the glaciers in the alps and the amount of man-made CO2 in the atmosphere. If not, that would mean he is denying any relationship between CO2 and temperature, which would disqualify him as a knowledgable person.


Are metals and other elements in every continent? I originally thought that you can only find certain things like iron, copper, and other things in certain places in the world and deep in mines but I saw in a few YouTube videos that you can find iron in rocks just laying on the ground. I searched for where copper comes from and it seems that, even though a lot of it comes from Chile, it can be found everywhere in smaller amounts. Is this true? Could I walk out into the woods right now anywhere in the world and find copper and iron?

Metals occur on every continent . The issue is whether or not they occur in sufficiently large deposits for them to be mined economically.
The difference between a mineral deposit and an ore body is economics: can it be mined for a profit?
One of the issues with mineral resources is that once they've been mined, they're gone.
Cornwall and Devon, in the UK, were once a significant producer of tin and copper.
Spain is major source of metals in Europe. Some of its mines were started by the ancient Romans. Poland too, has a active mining industry, as does Sweden.
Chile and Peru are major sources of copper, but copper is also mined in the US, Zambia, Australia and Russia.
Africa has a well established mining industry that mines many metals: gold, copper, iron, lead, zinc and platinum.
Metal mining in Australia and Canada provide both countries with significant sources of export income.
China has iron ore deposits that grade between 25 and 40 percent iron, but it prefers to buy higher grade iron ore, grading 65 to 70 percent iron, from elsewhere, mostly from Brazil, Australia and South Africa, because it is cheaper to produce steel from higher grade ore.
However, mineable quantities of some metals, such as lithium, platinum and rare earth metals tend to be concentrated in specific locations.


Are hurricanes/cyclones/typhoons in the Pacific Ocean usually larger than in Atlantic Ocean? Just my experience of observation: hurricanes/cyclones/typhoons in the Pacific Ocean seem to look larger than those in Atlantic Ocean (by looks I mean they occupy more grids in satellite images).

If this is true and if so, what is the reason for this? Is it because the Pacific Ocean has stronger hurricanes/cyclones/typhoons?

Typhoons in the western North Pacific ocean can be larger than hurricanes, because the great expanse of ocean water in the Pacific gives them more time and space to develop. Typhoon Tip in 1979 produced gale winds or higher over a diameter of 1400 miles. This is to my knowledge the largest western Pacific typhoon of record (it was also one of the most intense --- near-all-time-record maximum sustained winds of 190 mph, minimum barometric pressure an all-time record low of 25.6 inches of mercury). Typhoon Tip's 1400-mile diameter of gale-force or higher winds is almost double that of the largest hurricanes of record.


Why are solar longwave and terrestrial shortwave radiations neglected in radiation balance models? For an assignment I was given the question:

Explain why solar radiation is neglected in atmospheric “long wave” calculations and Earth radiation is neglected in atmospheric “short wave” calculations.

I realize that the wavelengths considered to be shortwave radiation are those smaller than or equal to 4$\mu m$. And I know that we say that as wavelength increases, radiation from the Earth increases while solar radiation increases.

As a result of this, Why are the sun's long-wave radiation and the Earth's short-wave radiation neglected?

Any explanation would be much appreciated!

It is because longwave (LW) correspond to a negligible part of the solar radiation and shortwave corresponds to a negligible part of solar radiation.

You can make an experiment yourself using NASA's Radiance calculator. By adjusting the parameters for Earth's and the Sun you will get the following plot of energy flux at different wavelengths

(The red line is the radiation spectra of the Sun and the blue line that of the Earth)

The cool thing about this tool is that you can see the actual data (or download it as a spreadsheet) and estimate the total energy flux between any range of wavelength (the area under the curve).

In this case, for SW radiation (0.1 - 4 $\mu m$) and LW radiation (4 - 100 $\mu m$) you get the following numbers

Sun LW: $1.98 \times 10^7 W m^{-2} {sr}^{-1}$
Sun SW: $1.95 \times 10^5 W m^{-2} {sr}^{-1}$
Sun Total: $2.00 \times 10^7 W m^{-2} {sr}^{-1}$

Earth LW: $1.24 \times 10^2 W m^{-2} {sr}^{-1}$
Earth SW: $1.82 \times 10^{-1} W m^{-2} {sr}^{-1}$
Earth Total: $1.23 \times 10^2 W m^{-2} {sr}^{-1}$

So in terms of percentages:

Sun: 99.03% SW and 0.97% LW

Earth 0.15% SW and 99.85% LW

That illustrate my initial point: LW is negligible for the Sun and SW negligible for Earth. Therefore, in simple models you can ignore both solar LW and terrestrial SW.

And why it is that way?

Well the reason is because the peak of the emissions decrease inversely proportional to temperature (according to Wien's law), while the total power grows MUCH faster, proportional to the fourth power of the temperature (according to Stefan-Boltzmann law). So the Sun been much hotter, produce an enormously larger amount of energy per square meter, but most of that energy is delivered in much shorter wavelength.

Note: It is interesting to note that despite that it is OK to neglect solar LW it is still 1580 times stronger than terrestrial LW.


Is the majority of Earth not unique? Realize that comparing planets is hard, but is Earth really that unique?

More to the point, if everything say 20-km below sea-level up into the exosphere disappeared (and the moon too) - what would be left to differentiate Earth from other planets?

Most notably, a moving Lithosphere. Shaving off the surface 20km (Lithosphere is~120km) would not stop plate tectonics. What makes Earth's surface so different is that it has a constant cycling of lithosphere; Dead planets are forced to keep surface scars caused by major impacts and weathering. To this date, we have not found another example of plate tectonics, though our ability to confirm this on other planetary bodies is limited.


Is there any possible way that a tropical cyclone of any strength could form over land? Most tropical cyclones rapidly weaken over land, however, given some conditions (such as very wet soil/ground cover and tropical lower atmospheric conditions) they can sustain themselves or even intensify over land, in a phenomenon known as the brown ocean effect. So, is it at all possible for extreme "brown ocean" conditions or other potential factors to result in not only the maintenance but the formation of a tropical cyclone over land, either from an extratropical system or not? The intensity and duration of time that the storm would last without transitioning to water is irrelevant—even a few hours at tropical storm levels would be a yes.

No, it isn't possible for cyclones, hurricanes and typhoons, which are all different names for the same thing, to form over land. Storms can form over land, but not hurricanes, which draw their power from the sun-warmed ocean and rapidly lose their strength when they hit land. The power of a typical hurricane is immense, probably in excess of 50 megatons, which was the yield of the largest hydrogen bomb ever tested (by Russia).


Why is Earth's age given by dating meteorites rather than its own rocks? Reading a course on Precambrian, I read that:

  Earth Age (around 4.5 billion years) is dated thanks to the meteorites hitting Earth during its formation rather than the inner materials composing the Earth.

Wouldn't it be more accurate by doing it with its inner materials? Why do we use meteorites if they hit the Earth after its formation?

Some background:

We are able to determine the age of certain rocks and minerals using measurements of radioactive and radiogenic isotopes of certain elements. The most common are U-Th-Pb, Rb-Sr and Sm-Nd. Simply put, the resulting date is the time that has passed from the crystallisation of that mineral. Obviously there are complexities, but there are not critical for this answer.

  Why do we use meteorites if they hit the Earth after its formation?

Short answer: because the meteorites formed together with the Earth and the rest of the Solar System.

Long answer: The Earth formed together with the rest of the Solar System and its meteorites around 4.5 billion years ago. When meteorites fall on Earth and you pick them up, you are able to date the time of their formation.

You say:

  Why do we use meteorites if they hit the Earth after its formation?

You have to distinguish the time that the meteorites form and the time that they hit the Earth. If I throw a meteorite at you, and you date it, it still records the formation time and not the time that I threw it at you. Hitting the Earth does not reset the radioactive clock in the meteorite's minerals.

  Wouldn't it be more accurate by doing it with its inner materials?

It would. There are two problems:

We don't have materials from the time of Earth's formation. The Earth is a dynamic place, and rocks are getting formed and destroyed all the time (also see related question). It may be that such old rocks exist on Earth, but because they are so old there are either metamorphosed and buried deep in the Earth or covered by sedimentary rocks. The oldest exposed rock on Earth available for study is the 4 billion year Acasta Gneiss in Canada. The oldest mineral on Earth is a zircon found in Australia, which is 4.4 billion years old. These are the only two materials that are known to be older than 4 billion years on Earth. There could be more, but we just couldn't find them.
The moon forming event occurred some tens of million of years after the formation of the Earth. This event destroyed the Earth's crust and any evidence of the age of the Earth, on Earth itself.

This is why meteorites are excellent for this task - they mostly formed during the formation of the Solar System.


Can Horizontal Radiation Fluxes Contribute to Net Column Heating? I've noticed that in many papers it's common to assume the (daily or longer averaged)  vertically integrated radiative heating can be expressed $F_z(\text{TOA})-F_z(\text{SURF})$, where $F_z$ is the vertical component of radiative flux, and $\text{TOA}$ and $\text{SURF}$ denote the top of atmosphere and surface respectively, with "top of atmosphere" usually either taken as $z\to \infty$, or as the tropopause height, depending on the context.
I assume this basically reflects the fact that if we express radiative heating $Q$ as a flux divergence $Q=\nabla \cdot (F_x,F_y,F_z)$, vertical integration gives
\begin{align}
\int_\text{SURF}^\text{TOA} Q \,dz &= \int_\text{SURF}^\text{TOA} \nabla_H \cdot (F_x, F_y) \,dz + \int_\text{SURF}^\text{TOA} \frac{\partial F_z}{\partial z} \,dz \\
&= \int_\text{SURF}^\text{TOA} \nabla_H \cdot (F_x, F_y) \,dz + F_z(\text{TOA})-F_z(\text{SURF}).
\end{align}
It seems natural to assume the $\int_\text{SURF}^\text{TOA} \nabla_H \cdot (F_x, F_y) \,dz$ term, which is the net horizontal flux divergence out of the column, will be small compared to the $F_z(\text{TOA})-F_z(\text{SURF})$ term, but does anyone know just how much smaller? What are some reasonable scale estimates for these terms? Are there situations in atmospheric science where net horizontal radiative flux divergence can't be neglected?
For example, I'm imagining a column with a single spherical cloud in it, and the sun directly overhead, but no clouds in any other nearby columns. In such a situation, wouldn't there be a horizontal radiative flux divergence, i.e. a net horizontal radiative flux out of the column? Would this effect still have a negligible impact on net column heating, or does nothing like this occur in real atmospheres?

Yes, there are horizontal radiation fluxes. These can change the heating rate by 10-40 K hr$^{-1}$. They also change depending on the extent of the atmosphere you may be considering. One can also imagine that they are a bit stronger during the sunrise and sunset, when the sun is not directly overhead and the beam has a larger horizontal path length.
There is work, such as the Neighboring Column Approximation which tries to get around that. There's another paper, but I can't find it right now that also tries to resolve this issue.


What evidence is there for geological mechanisms that formed the Siberian traps flood basalt? The Siberian Traps are the modern day remnants of the flood basalt event.  Its eruptions is widely believed to be a major contributing factor of the Permo-Triassic extinction event.

In reading several sites on the matter, there seems to be two possible mechanisms (from the Wikipedia page linked above):

  The source of the Siberian Traps basalt has variously been attributed to a mantle plume which impacted the base of the earth's crust and erupted through the Siberian Craton, or to processes related to plate tectonics. Another possible cause may be the impact that formed the Wilkes Land crater, which may have been contemporaneous and would have been nearly antipodal to the Traps.

The statement concludes with:

  This controversial scientific debate is ongoing.

What evidence is there that would pinpoint which of these mechanisms (or any other) resulted in the Siberian Traps flood basalt eruptions?

This answer will focus on recent research evidence found within the Siberian Traps deposits.  For the purposes of this answer, the theory that a possible Wilkes Land impact resulted in the Siberian traps as an antipode volcanic response will not be included (please see the question and answer to Can impact events cause widespread volcanic activity on the other side of the planet? for details of current modelling doubts of this mechanism).

Many researchers cite that the initial cause of the Siberian Traps was a mantle plume, some refer to it as a 'superplume' that inpinged into the upper mantle, as shown in the diagram below:

Image source: The Permian Period, Palaeos.

However, according to Sobolev et al. (2011), observations and measurements of the region affected by the Siberian Traps exhibit no evidence of pre-magmatic uplift nor lithospheric stretching that can be associated with mantle plume activity (e.g. the Afar Region in Ethiopia), their models suggest that there was extensive plume erosion of the cratonic crust over a considerable length of time.

Petrological evidence by Sobolev et al. (2011) suggest that some recycled oceanic crust existed at the head of the plume. This contamination was noted in $\delta^{34}\ce{S}$ analysis of melt inclusions by Bryan and Ferrari, (2013) and Black et al. (2014), who determined that the mantle melt source was close to that found in mid-ocean ridge basalts.

Black et al. (2014) also note that a significant contributor to $\delta^{34}\ce{S}$ (up to 25%) was derived from evaporitic sources. This related to the observations made by Jerram et al. (2013) of the contact metamosphism around the doleritic dykes and sills, indicating that the basaltic magma was injected into an organic and salt rich sedimentary basin.  This interaction between the organics an salt and molten rock would have released halocarbons, $\ce{CO2}$ etc that are attributed to the mass extinction at the time (Jerram et al. 2013; Self et al. 2014).

This, and the prevalence of tuff leads to Jerram et al. (2013) questioning whether the Siberian Traps were the result of widespread explosive volcanic activity, related.  The dyke and sill intrusions are believed to have caused episodic explosive eruptive sequences, according to Self et al. (2014).  Some of these eruptions were phreatomagmatic depositing mafic volcaniclasts according to Bryan and Ferrari, (2013).

As, the crust eroded due to the plume (Sobolev et al. 2011), the eruptive sequences transitioned to basaltic lava flows, these are believed to have also been episodic, according to Self et al. (2014) with pulses of magma production and lava eruptions.

The map below shows the distribution of sill intrusions, pyroclasts and lava of the Siberian Traps.

Image source: IAVCEI - the red are sill intrusions, the light purple are pyroclasts and the dark purple is lava.

References

Black et al. 2014, Sulfur isotopic evidence for sources of volatiles in Siberian Traps magmas, Earth and Planetary Science Letters

Bryan and Ferrari, 2013, Large igneous provinces and silicic large
igneous provinces: Progress in our understanding
over the last 25 years, Geological Society of America Bulletin

Jerram et al. 2013, What happened at the start of the Siberian Traps? Understanding the onset of flood volcanism, American Geophysical Union, Fall Meeting 2013

Self et al. 2014, Emplacement characteristics, time scales, and volcanic gas
release rates of continental fl ood basalt eruptions on Earth, The Geological Society of America
Special Paper 505

Sobolev et al. 2011, Linking mantle plumes, large igneous provinces and environmental catastrophes, Nature


Carbon's role in ocean acidification This might seem like a basic question, but I'm a little confused about the effects on ocean acidification of different carbon compounds.

I have heard that increased levels of carbon dioxide in the atmosphere are causing ocean acidification, lowering the ocean's pH.

I have also heard that shellfish like mussels and oysters can be used as a carbon sink, making shellfish farming a form of carbon sequestration. This makes sense, as their shells contain carbon in the form of calcium carbonate.

My question is how does such sequestration affect ocean acidification? On the one hand, sequestering the carbon as calcium carbonate would lower the carbon presence in the ocean, which would seem to reduce the effects of CO2. On the other hand, calcium carbonate is alkali: leaching minerals from the ocean to form such shells would seem to increase acidity (since the opposite process, dissolving calcium carbonate, reduces acidity).

In answering this complex question, I think it's important to consider the form of carbon that is utilized and the overall reactions involved (warning: somewhat lengthy diversion ahead, and advance apologies if such is already understood by this audience). In the long-term carbon cycle, atmospheric $\ce{CO_{2,(g)}}$ drives weathering on land, importantly of silicates. $\ce{CO_{2,(g)}}$ dissolves in pure water as aqueous ion ($\ce{CO_{2,(aq)}}$) and carbonic acid ($\ce{H_2CO_{3(aq)}}$).
$$ \ce{CO_{2,(g)} + {H_{2}O_{(l)}}  <=> {H_2CO_{3,(aq)}} }$$
but true carbonic acid is unstable, and the vast majority of this total dissolved carbon is thus present as the aqueous ion $\ce{CO_{2,(aq)}}$, with concentrations obeying the simple Henry's law relation (not shown). We can write this net reaction is
$$ \ce{CO_{2} + {H_{2}O}  <=> {H_2CO_{3,(aq)}} <=> H^{+}_{(aq)} + HCO_^{-}_{3,(aq)} }$$
Bicarbonate also reflects the association/dissociation reaction involving pure carbonate ion,
$$
\ce{H^{+} + CO_^{2-}_{3} <=> HCO_^{-}_{3}}
$$
Weathering of a continental silicate, e.g., a normative wollastonite (chosen for simplicity), can thus be written as$$
\ce{ CaSiO_3 + H_{2}O +2CO_{2} -> 2 HCO_^{-}_{3} + Ca^{2+} + SiO_{2}}
$$
The important point is that the dissolved carbon delivered to seawater by continental weathering is as bicarbonate, and surface seawater pH ($\sim 8)$ in approximate equilibrium with atmospheric $\ce{CO_{2}}$ indeed reflects this distribution of dissolved species. If we write the equilibrium for skeletal calcium carbonate as
$$\ce{ CaCO_{3} <=> CO_^{2-}_{3} + Ca^{2+}}$$
we can combine the above equations to give the overall reaction for the dissolution/precipitation of $\ce{CaCO_3}$ in seawater (incorporating the mass balance on $\ce{CO_2}$ from reactions 1, 2, 3, and 5 -- sorry I can't get MathJax to turn equation numbering on) as,
$$
\ce{CaCO_{3} + H_{2}O + CO_{2} = Ca^{2+} + 2HCO_^{-}_{3} }
$$
Thus in this context, an important result is that, in the overall mass balance associated with precipitation of $\ce{CaCO_{3}}$ (i.e., driving the above reaction to the left), $\ce{CaCO_{3}}$ serves as a source, not a sink of carbon, because it liberates one mole of $\ce{CO_2}$ originally delivered as bicarbonate to seawater from silicate weathering. In the larger view (long term geochemical cycling), marine carbonates are a temporary sink for carbon that is ultimately subducted and returned to the atmosphere by vulcanism and other magmatic processes. The carbonates residing on the continents today (e.g., Paleozoic) have, in contrast, a much longer residence or cycling time that their modern pelagic equivalents.

Now, to your question: ocean acidification (titration of seawater by atmospheric $\ce{CO_2}$, driving the last reaction to the right) per se is buffered by the attack of this sink of $\ce{CaCO_3}$ producing more bicarbonate. Sequestration of carbon by growing shellfish will, according to the above, consume (some of) this bicarbonate, and produce $\ce{CO_2}$ as a result. The larger, key question to me, is the rate at which the existing store of sedimentary $\ce{CaCO_3}$, particularly in surface water where it is being formed, dissolves in response to this attack.

Edited for clarity, typos


What is this canoe-shaped rock with obsidian? flakes? I found this rock near my home in the high desert of south central Utah (near Capitol Reef National Park). The sides are symmetrical and smooth -- shaped somewhat like a canoe. It is 6 1/2" long; 1 1/2" at widest point. The top is sheared off and sparkles in the light. It is embedded with flakes of a shiny, black glasslike material, possibly obsidian. The Fremont culture occupied the area and left an abundance of tools, points, and chip rock, many of which were sourced from elsewhere; most likely the result of trading. A neighbor and I came up with an uninformed theory. Would appreciate any informed observations.

Black elongated crystals are mostly hornblendes. The rock itself is (probably) horblende andersite or hornblende dacite. Both are intermediate volcanic rocks.


High resolution DEM for digital soil mapping and modelling I am carrying out an exercise on digital mapping of soil properties. I have tried several high resolution DEMs like 90 m and 30 m but their resolution is not good enough. Kindly assist.

It depends on your area of interest. If you are just testing a method, one of the large coverage free DEMs with high resolution (2m) is ArcticDEM, but as its name say it covers the Arctic only (Alaska, Northern Canada, Northern Europe, Russia, etc.). You can check that one out (ArcticDEM)

This is the coverage of ArcticDEM


Is there a meaningful concept of a mountain having a footprint area? Is there a meaningful way to delimit a mountain as an area with a sharp boundary? Looked as as a 2D shape on the datum it would be a footprint of the mountain similar to a building footprint, while as a region cut out of the surface it would delimit the surface of the mountain from surface that is not port of the mountain.

Obviously there's going to be some degree to which this is arbitrary but it seems like some function of slope, aspect, elevation etc ought to be able to produce some meaningful partition of the earth's surface.   I would like to know if any concept like this is used at all, how it's defined, and how well it corresponds with the intuitive sense of one point being part of a mountain, another point being part of a different mountain, and a third point not being part of any mountain.  If it's just completely unworkable despite the intuitive appeal, then a reasonable explanation of why is an acceptable answer.

The mountain you see is only a part of the story. From a geological view all mountains have roots, in which the weight of the mountain depresses the upper crust into the lower crust (occasionally with gravity inversion, as in salt diapirs), and the overall crust is depressed into the upper mantle. This results in a regional gravity anomaly which could be regarded as one form of the mountain footprint. That is, a map of the deviation of the mountain's 'Bouguer anomaly', away from the regional gravitational envelope.
But that's just a geophysical perspective. You could doubtless develop comparable 'footprint definitions' from a hydrologic or geomorphologic perspective.


Why don't lightning strikes cause a lot of injury or damage to property? We hear about people being injured or killed, or property being damaged or destroyed, by flash floods all the time. Or by straight line winds. Or by hail. Or by tornadoes. Why not lightning?

Annually, about 51 people die from lightning strikes per year in the United States. Part of the reason is the low probability of being hit by lightning. Tornadoes, hail, and straight line winds sweep large areas, while one lightning bolt covers a rather small area, and may even be harmless if it doesn't make contact.

Think of it this way: if you were struck by lightning, a person 500 feet away may not be harmed by it, but if straight line winds cause your house to collapse, you can say with relative certainty that your neighbor will have some damage.

Another factor is the reliability of protection. Major hail can total a car. Strong straight line winds and tornadoes can collapse or remove your house. A lightning bolt will cause property damage, but you will be safe inside, provided you aren't touching metal.


How should one compare the comfort of climates? Is there a way to measure the overall feel of the weather for a place?

Suppose that:
Place A has Temperature $33^o C$, Humidity $57\%$, Wind $14\;km/hr$, and Precipitation $20\%$
Place B has Temperature $37^o C$, Humidity $11\%$, Wind $14\;km/hr$, and Precipitation $0\%$

Which place would feel better?

One measure that could be used is the apparent temperature, which combines air temperature, humidity and wind speed to derive the temperature that the human body feels. It is sometimes referred to as the "feels like" temperature or the Steadman temperature, after Robert Steadman who proposed the idea in 1971.

The formula used by the National Oceanic and Atmospheric Agency, for calculating the apparent temperature is:

 AT = -2.7 + 1.04*T + 2.0*e -0.65*v

where AT and T (air temperature) are °C, e is vapor pressure in kPa,
and v is 10m wind speed in m/sec.

Most weather oraganizations include the calculated apparent temperature in their weather reports.


Why do the vast majority of the world's deserts fall on the tropic of capricorn or cancer? I noticed on google maps today that the earth has two very distinct regions on which the majority of deserts are located. These fall on the tropic of capricorn and cancer. Illustrated here:

What causes this?

At thirty to thirty-eight degrees north and south of the equator are the so-called Horse Latitudes, regions with constant high-pressure systems. These regions inhibit precipitation. The phenomenon is quite well described and illustrated on Wikipedia:
https://en.wikipedia.org/wiki/Horse_latitudes


How are critical loads of nitrogen deposition on eco-regions determined? Natural habitats have a "critical load" threshold in regards to deposition of nitrogen compounds (both wet and dry deposition).  The critical load is calculated in kg N / hectare and is specific to local ecoregion type.  I've heard that critical loads are based on lichens or other simple vegetation, but I'm not sure.  How are critical loads calculated?  What are the factors that are considered?

An example of critical loads are shown below for the western USA. In general the ecoregions are pretty coarse and in my mind over-generalized.  I'm curious about how these ecoregion distinctions are made.  How many types of ecoregions are there and what are they based on?Is it based on the vegetation that currently exists in that area (which can sometimes be distinctly different than indigenous vegetation)?  Or is it based on some historical vegetation type?  Furthermore, what is the expected result if deposition surpasses the critical load and what is the time horizon involved? !

These two links were the sources I used when researching this question:

"Mapping critical loads of nitrogen deposition for aquatic ecosystems in the Rocky Mountains"

http://co.water.usgs.gov/publications/non-usgs/Nanus_2012.pdf

"Approaches for estimating critical loads of nitrogen and sulfur deposition for Forest Ecosystems of U.S. Federal Lands"

http://www.nrs.fs.fed.us/pubs/gtr/gtr_nrs71.pdf

It looks like there are actually several different approaches which can be used when calculating the Critical loads, and depending on the approach the factors considered change:

Empirical (Regression) modeling: These are generally based on observations of ecosystem response (this is tracked off of Foliage, lichens, or soils) and tracked to a given deposition level. This is generally calculated in one area, and applied elsewhere.
Simple mass-balance models: estimating a net loss or accumulation of nutrients based in the in/out of a system for that nutrient. These are basically steady state models and are measured generally on base cations or nitrogen.
Dynamic models using a mass balance approach which incorporates internal feedbacks over time. This is a combination of the two and is generally used where there is an abundance of existing data.

The links contain further information which may be more helpful.

According to "Wolfe, A.P., Baron, J.S., Cornett, R., 2001. Anthropogenic nitrogen deposition induces rapid change in alpine lakes of the Colorado Front Range (USA). Journal of Paleolimnology 25, 1e7." as cited in the first article I linked, This excess N (caused by exceeding the critical load) can result in acidification and nutrient enrichment, increasing primary productivity in high-elevation lakes and streams, and altering diatom community structures that form the base of the food web –

The USFWS Ecoregion classification system was designed by Robert G. Bailey working out of the Rocky Mountain Research Station in Colorado. In his paper, "Identifying Ecoregion Boundaries" found Here: http://www.fs.fed.us/rm/ecoregions/docs/publications/identifying-ecoregion-boundaries.pdf  he outlines the rational used for identifying the boundaries, and the 20 different principals he used. They are: 1. The series of ecoregions should express the changing nature of the climate over large areas. 2. Boundaries of ecoregions coincide with certain climatic parameters, 3. , 4. , 5 - 20


What causes these circular swirls of islands? I was following the boarder of the US and Canada on Google Maps, because, and found these interesting circular patterns of islands near the Northwest Angle. I have heard of geologic folding but I have never heard of Swirls or Circles. What is the cause of this?

Swirl of islands on Google maps

Near the Lake of the Woods, the island swirl or vortex is due to structures in bedrock beneath the lake.  The rocks in this area are old and have been folded by tectonic action. The area has either been folded into a dome or a basin, exposing different layers of bedrock. Glacial activity afterwards has 'flattened'the area, and differential erosion within the folded area formed valleys that flooded where the rock eroded faster.

Geologic history of The Lake of the Woods.


Which crops are especially sensitive to atmospheric ozone? In this National Park Service article, the effects of ozone on trees is discussed:

Ozone enters plants through leaf openings called stomata and oxidizes plant tissue, causing changes in biochemical and physiological processes. Both visible foliar injury (e.g., stipple and chlorosis) and growth effects (e.g., premature leaf loss, reduced photosynthesis, and reduced leaf, root, and total dry weights) can occur in sensitive plant species. Many other factors can magnify the extent of ozone injury such as soil moisture, presence of other air pollutants, insects or diseases, and other environmental stresses.

I assume that ozone can adversely affect many types of plants, including agricultural crops.  Which crops are especially sensitive to atmospheric ozone?

I could find a relatively recent review by Mills et al. (2007) that lists sensitivity to ozone for several crops. Among the most sensitive were (table 1)

Watermelons (albeit with very few data points used)
Pulses
Cotton
Wheat

While the most resistant crops were

Barley
Fruits (Plums and Strawberries)
Broccoli

The measure for ozone used in this review is AOT40, which accounts for accumulated ozone levels over 40ppbV within the time from 8AM to 8PM.


What are the major contributors to the amount of infra-red emitted by the earth? From the answers from an earlier question, I learned that most of the solar radiation gained by the earth system (atmosphere, surface, and inner mass) is re-radiated back into space in the form of infra-red. This balance of incoming solar radiation and outgoing infra-red radiation depends on the earth system's infra-red radiation 'equation' - that is, how it takes 'in' the various forms of solar radiation and converts them into infra-red. At least, that's the best I can make out of this article Earth's Energy Budget and this accompanying chart.

My question is what are the principal components of this 'equation'? I imagine the percentage of water in the atmosphere and on the surface of the earth, the mean absorptive ability of the non-water surfaces of the earth, and, what is most mysterious to me, what is the 'factor' of infra-red production by different surface materials. I imagine this is all highly technical and finely detailed in large elaborate models, but are there 'big levers' that represent most of the infra-red radiative effect? Where I am 'headed with' this, of course, is if there is a practical way to increase this radiation back to space that can make a positive difference on global warming (ie net positive radiation into space after accounting for increased greenhouse gases back radiation)? And I imagine there is not, given we are not trying that.

It depends on the wavelength.

The figure shows the most absorbing species between 6 and 16 µm for a U.S. standard tropical atmosphere (Note: this figure does NOT include the Earth's surface!).  Absorption data is taken from Anderson et. al (1986) and simulations are performed with the open-source Atmospheric Radiative Transfer Simulator (ARTS; Eriksson et al., 2011).  The plotting was carried out with LaTeX and pgfplots.  ARTS is open-source and includes the Anderson et al. data, so you can try different wavelengths for yourself.

Depending on wavelength, we have dominant absorption from H₂O, O₃, CO₂, N₂O, CH₄, and others.

I have also uploaded a PDF version (PDF, 117.68 mm × 228.21 mm, 5.1 MiB) for higher-resolution viewing.


Why is continental crust less dense than oceanic? Why is it that continental crust is less dense than oceanic, where in fact continental crust is thicker than oceanic crust?

Thickness has nothing to do with density. The density is how much a given volume weighs. If a block of 1m × 1m × 1m weighs 60kg, and another block the same size weighs 100kg, then the second block is more dense than the other.

So if the material that makes up the continental crust is less dense, then the continental crust will be less dense.

This almost sounds like a homework question, so I will leave references and such for now, but finding densities and compositions of these varying crusts is not too difficult.


In the oil field, when a vertical cylinder coring sample is taken, how is the core severed at the bottom and removed from the formation? I would like to know how the core is cut off at the bottom of the drill. I also would like to know how the core is brought up to the surface without slipping out and falling back down.

Coring is an important method to get detailed information about the formations, however, it's very time-consuming and costive, so it's only applied when geologists and reservoir engineers need high-resolution data. It is more common in ore prospecting and mining, mapping for infrastructure and basic geological understanding of the 3-dimentional structures. Lake sediment cores are used for varve chronology. Marine sediments are cored to understand the oceanographic development, date events as slope processes and changes in glaciation and climate. Ice is cored to measure variations in the atmosphere to understand past climate and vulcanism.

To sum up, coring is a very important tool for geologists, not only in oil fields. Cheaper, and faster, alternatives to coring is mud logging, a very common practise when drilling in oil fields.

So how to get the cores up from the borehole?

There are some different systems used, depending on the rock/sediment and investment involved.

For deep drillings in hard formations, a core catcher is used in a two-barrel system. The corehead (the drill bit) is connected to the outer barrel, while the core is pushed into an inner barrel. The lower part of the inner barrel is called the shoe just above the drill. In the shoe, there is a core catcher that wedges between the barrel and the core. The core catcher is a split ring with a rough inside that holds the core. When you pull the core, it snaps off as the lower and upper shoe squeezes the catcher. The core catcher works somehow like an expansion anchor, but inverted, grabbing the core on the inside of the barrel rather than the wall on the outside. The inner barrel also protects the core from the rotating outer barrel.

For softer sediments, the core catcher is made out of springs that close inwards as the core is pulled. It is sometimes called basket retainer and can be in metal or plastic.

For smaller gravity corer, there is a valve on top of the tube that is closed and the underpressure in the tube holds the core in place. Sometimes...

Check the linked pictures, they probably explain better how it works, but I couldn't find any good CC.


Why are "ground level" air quality monitors really on rooftops? There are many papers that talk about the air quality at ground-level in cities, observed by air quality monitors.  Some monitors are located above the building(not actually on the ground). For example, my lab's equipment was located on the 5th floor of the building (~ 15m).

My questions are:

Is it appropriate to represent air quality using measurement data on a building roof?
What's the difference between air quality on the ground & the roof? And what matters?

In order to put your question in perspective, you need to consider atmospheric mixing and the size of the system you are curious about.  The troposphere is several kilometers thick and the mixed layer of atmosphere above the ground can occupy a significant fraction of the troposphere.  Granted, during cold events, the temperature of the air can be so cold that the lack of convective motion creates a very shallow (e.g. 10s of meters) mixing layer.  Though, 15 meters above the ground will virtually always be within the mixed layer near the ground, despite cold weather events.

Some people do measure air quality at the ground level, but it is generally done in the context of studying biogenic emissions (e.g. soil emissions or below-canopy tree emissions).  However, those are special field studies, which have different objectives than typical air quality monitor sites.

Typical air quality monitor sites are relatively sparse, and even large cities have just a few monitors.  Generally, monitors are located in such a way that they are observing well mixed air, so that it represents air quality in the region.  It is imperative that you put your air quality monitor high enough above the ground so that it isn't being directly influenced by emission sources (e.g. your neighbors wood stove, or a car's tailpipe).  Otherwise, if you put the monitor literally on the ground, you will often be observing much more variance, with higher peaks that represent that specific location only.  See this post for more info on how monitor locations are selected.  You can also see this EPA handbook on siting monitors which notes:


The effect of CO2 concentration on the pH of the ocean I'm confused about how increased $\ce{CO2}$ concentration in the atmosphere affects the pH of the ocean.

The increase in $\ce{CO2}$ concentration means the pH of the ocean will decrease (by several chemical reactions). However, as there is more $\ce{CO2}$ in the atmosphere, ocean temperatures will rise meaning the ocean will absorb less $\ce{CO2}$, likely slowing down ocean acidification.

In short, the rise in $\ce{CO2}$ seems to have two contrasting effects on the pH of the ocean. Am I interpreting this correctly? If so, how is ocean acidification a problem?

For reference, the article I read is Barker and Ridgwell (2012), Ocean Acidification, Nature Education Knowledge.

Increasing CO2 concentration in the atmosphere is leading to an increasing concentration of dissolved CO2 in sea-water. The dissolved CO2 then reacts with the water to create carbonic acid, decreasing the pH as recognised in the question.

The solubility of CO2 in water does decrease with increasing temperatures, so the maximum amount of CO2 that can be dissolved is being decreased as global temperatures rise, but the oceans are not yet saturated. There is a some further discussion and references om this page by NASA: The Oceans Carbon Balance.

Should global temperatures reach a point at which the oceans are saturated and start to release CO2 that they have been absorbing since the start of the industrial revolution, there would be very serious consequences for us all. This is, naturally, the subject of much ongoing research, e.g. Ocean-Atmosphere CO2 Exchange.


When calculating flood recurrence intervals, do you use annual instantaneous peak flows? I would like to calculate the bankfull flow for a certain point on a river.  The recurrence interval of bankfull flow varies for different rivers, but is typically always found to be between 1 and 2 years.    Let's imagine I decide to set the recurrence interval at 1.67 years, which gives me an exceedance probability of approximately 60% ($\rm Pr(X\geq0.60) = Pr(X\leq0.40)$).

Supposing I have a stream gage at the point I am interested in estimating bankfull flow for, and I recorded hourly discharge values for 20 years, which set of values should I use to calculate the recurrence interval? Should I determine the value associated with this exceedance probability using all hourly flows, the daily mean flows, the annual high flows (what the USGS calls instantaneous peak flows), or some other subset of values?

I think you should just follow the guidelines provided by the USGS for this calculations (http://water.usgs.gov/osw/bulletin17b/dl_flow.pdf). From there you can read:

  "Flood events can be analyzed using either annual or partial-duration series. The annual flood series is based on the maximum flood peak for each year. A partial-duration series is obtained by taking all flood peaks equal to or greater than a predefined base flood".

They also provide a list of FAQs (http://water.usgs.gov/osw/bulletin17b/bulletin_17B.html) and a way to calculate them.


Could a firestorm create a hurricane-like cyclone? Mesocyclones form when air rises and rotates in a "pillar" of sorts. It's sometimes associated with thunderclouds and tornado formation.

A certain kind of cumulonimbus, the cumulonimbus flammagenitus, can form above a firestorm of sufficient strength (magnitude, temperature, whatever the thing being measured is). Some cumulonimbus flammagenitus clouds have generated true fire tornados (as opposed to the fire whirl, which is commonly called a fire tornado) indicating that these clouds do form mesocyclones.

My question is, could a firestorm generate a hurricane-like cyclone, with strong surface winds along a large area, raining ash and embers? If so, would it move or be stationary? How long could it sustain itself? What would be involved in its formation?

I don't think so. A large fire could generate a circulation with strong low-level convergence and upper level divergence that would cause subsidence as the air radiatively cooled. If the fire were stationary and huge, the Coriolis effect could make it's upper level outflow turn, but I don't think an intense hurricane-like cyclone could form unless the fire were actually relatively small (like the eyewall of a hurricane), but in that case I'm not sure that the necessary pressure gradient could be maintained (even if the fire could somehow continue to be fueled).


Global warming and winter temperatures What causes cold temperatures to move earlier than they usually move? Here in Buffalo the weather was 9 °C. However, everyone had winter coats and hats on. There was no snow, but it was very very cold. I have a feeling that the Great Lakes may have something to do with it.

The Great Lakes contribute to a huge thermal inertia, which will even out short-term temperature fluctuations, and delay the smoothed seasonal temperature peak. On the other hand, more sinuous looping of the jet stream  is likely to have a comparable, if not larger, effect upon the temperatures in Buffalo. The process is this: As global warming progresses there is a disproportionate warming towards the polar regions. This results in a reduced temperature gradient with respect to latitude. It is this gradient which is largely responsible for the jet stream intensity. As the jet stream weakens it becomes more sluggish and sinuous, resulting in regional hot and cold anomalies. If Buffalo happens to get caught in one of these jet stream loops, it is quite possible to have periods of anomalously low temperature, even though there is an overall North American warming. It is also possible for Buffalo to get caught in a negative loop, and hence experience anomalously hot temperatures.


Connection between microbes and serpentinite? Serpentinite belongs to the serpentine group. This group of minerals are metamorphic minerals caused a special process called serpentinization.

Serpentinization created serpentinite on the Earth's deep sea floor. Serpentinite is paramagnetic which creates a magnetic field for the mineral.

While researching this unusual mineral scientists found microbes within its structure. After study scientists suggest that these microbes are the origins of life.

What is the connection  between the microbes and serpentinite?

The most common explanation for microbial activity in serpentinites is the exploitation of abiogentic hydrogen and methane formed during the serpentinisation process.

Quoting the abstract of a recent authoritative review:

  The process of serpentinization creates strongly reducing conditions and produces fluids that are highly enriched in molecular hydrogen and methane. Some microorganisms are able to exploit these compounds to gain metabolic energy and to generate biomass, leading to the development of biological communities based on chemical energy rather than photosynthesis. The abundance of chemical energy and favorable conditions for organic synthesis make serpentinites a strong candidate for the site of the origin of life on Earth, as well as a prime target in the search for life elsewhere in our Solar System.

From Serpentinites, Hydrogen, and Life (may be paywalled).

You might also find this review interesting: Serpentinization, Carbon, and Deep Life (should be free to access).

These two papers present the current thinking in this subject.


Are we now and/or have we been in the RCP8.5 scenario? Is it generally understood that we (globally) have been living in an RCP8.5 scenario over the past 7-8 years?

Such that a predictive climate model using RCP8.5 assumptions that was run circa 2011 can be considered indicative of the time between then and now?

I am working on a calibration of modeled dry-bulb temp data versus real observations over the intervening years but I realize that any correction I come up with would necessarily have any deviation from reality and RCP8.5 baked into it.

In short, I would say that it is too soon to say. But, if I were forced to guess: I would indeed incline to say that we live in a RCP 8.5-ish scenario.

I'm not an expert at all on climate models or RCP scenarios, but I found the question interesting, so this is my attempt to answer it based on the most reliable data sources I found. I hope to motivate expert to jump in to comment, improve, challenge or support this answer.

RCP scenarios

The scenarios involve future pathways in the emissions of a large range of different chemicals (Greenhouse gases and aerosols), so if we look at how actual emissions of $CO_2$ have matched the scenario we might think we are in one scenario, but is we instead look at the emissions of $NH_3$ we might find ourselves in another scenario. The best way to summarise all those different parameters is to consider the total radiative forcing, that is the combined effect of all those compounds in Earth's energy balance. In fact the numbers that label the different RCP's are the expected total radiative forcing by year 2100 in $W/m^2$.

The following figure shows the radiative forcing (this time as $CO_2$ equivalent) of each scenario. And as you can see, by 2018, the differences are so small that I think it is too soon to say with any reasonable certainty that we are flowing one or another scenario.

(Figure from Wikipedia commons originally here)

Scenarios versus measurements

Nevertheless, we can attempt to plot the actual measurements against what was predicted  by the scenarios. The best variable to contrast would arguably be the total radiative forcing. However, that is a quantity difficult to calculate and I haven't found published values like those in the IPCC Assesment report 5 (AR5) Annex II table AII.1.2, beyond 2011. Up to that year, the forcings were beautifully summarized in figure 8.18 of AR5 chapter 8:

Given the lack of total radiative forcing data, we can instead make the comparison with some other variable. Such analysis will be liable to depend on the chosen variable as pointed out before. Therefore, to minimize that problem let's pick a variable with a large influence in the difference between the four scenarios. I think that would be $CO_2$ emissions from fossil fuels and industry.

The the emissions predicted by each scenario can be obtained at the RCP Database (version 2.0). That data looks like this:

Now, for the actual estimated emissions, perhaps a reliable source is the Global Carbon Project, that provide the emissions data up to 2016. Putting all that together we get the following figure:

So, it looks RCP8.5-ish, but the differences between the scenarios are still quite small, so it is difficult to say.

Another good variable to compare would be $CO_2$ concentration, that can be directly measured instead of just estimated. In that case using NOAA's Global Greenhouse Gas Reference Network data for global $CO_2$ concentration, against the ones prescribed for each scenario (taken as well from RCP Database (version 2.0)) the figure looks like this

That looks more like RCP4.5-ish. But again, probably too soon to say.
Also, it might be that even given more time, the path followed by the climate system would be like one RCP in some aspects and like other RCP in other aspect. For example, $CO_2$ emissions might follow roughly RCP8.4 but methane emission might follow RCP4.5. Or somewhere in between.

Another approach would be to use use an actual climate model forced by RCP8.5 (not just the RCP), so you can compare mean surface temperature, but that would be tricky for many reasons and also model dependent.

If anybody knows of published estimated total radiative forcing from 2012 onward, that would be nice to add and compare. It might make the answer a bit more clear but I think that in any case, it is too soon to give a definite answer.


Why do most seismic inversion methods ignore high frequencies? Different post-stack inversion methods such as model based, sparse spike, colored and recursive inversion methods use high cut frequency impedance logs (low frequency) and mid-frequency seismic trace in order to generate an inverted impedance model. Then why are high frequency components are not taken into account during inversion?

Because those frequencies are not present in the seismic data.

Here's an example with some typical numbers:

Seismic sample interval: 4 ms
Therefore Nyquist is 0.5 $\times$ 1/0.004 = 125 Hz
Usually there is a filter on the recorder at 0.8 $\times$ Nyquist = 100 Hz
So the seismic does not contain frequencies beyond 100 Hz

The maximum frequency $f_\text{max}$ of the data determines its resolving power. There are various ways to think about and calculate this; here's one formula (Kallweit & Wood, 1982):

$$\tau_\text{min} = \frac{1}{1.4\,f_\text{max}}$$

So in our example, the thinnest resolvable bed is about 1 / (1.4 $\times$ 100) = 7.1 ms, and it will be thicker than that if there is a lot of noise or the bandwidth is not optimal (the earth attenuates high frequencies more than low ones, so this is an absolute minimum).

If we assume a P-wave velocity of 2500 m/s, then 7.1 ms two-way time is about 2500 * (7.1/2) = 8.9 m (55 ft). Ordinary wireline logs have a resolution of 0.15 m or 6 in, so there's a substantial discrepancy. I call this 'the integration gap'.

Because the seismic contains no information about geology thinner than this 8.9 m (in this example), not only is it pointless trying to invert for it, but it would be dangerous: anything we thought we'd resolved would be erroneous. This is why it's necessary to filter the logs back to the resolution of the seismic.

Reference

Kallweit, R & L Wood (1982). The limits of resolution of zero-phase wavelets. Geophysics 47 (7), p 1035–1046, DOI:10.1190/1.1441367.


How can daily brightness be quantified or measured? It occurred to me that there might very will be a metric out there that measures and quantifies "daily brightness". Meaning, how bright any given day is, taking weather conditions and cloud coverage into account.

A general brightness metric is lumens, but I can't find anything on this subject with respect to meteorology.

And, if such a metric does exist, what's its range, 0 - 100? What weather/ambient conditions are represented at this range's extrema?

It can be measured in units of energy per surface area, for example, kWh/m2.  The official SI name would be radiant exposure but I haven't seen that phrase used in a climate or weather context.

For example, here is a map by NREL of average radiation per day in the US for July:

(Source: National Renewable Energy Laboratory)

And here is a map for Sweden for the same quantity per year (hence the much larger numbers):

(Source: SMHI)


How it's possible to measure temperature 2000 years ago with such precision? I saw this graph about the global temperature, it goes back for 2000 years.
How is it possible to measure temperature 2000 years back with such a precision of like ~0.1 C?
The image from Reddit post I don't know the source of original data.
What tools are used to measure it?

How it's possible to measure temperature 2000 years ago?

Sans the technology used by Bill and Ted ("Bill and Ted's Excellent Adventure"), it obviously is not possible to directly measure the temperature from yesterday, let alone 2000 years ago, or longer. What is used are "proxies", things that can be measured today that serve as stand-ins for things such as temperature in the past.
One example of a proxy is the amount of oxygen-18 in the ice in Greenland and Antarctica. Water with two hydrogen atoms and one oxygen-16 atom has a boiling point of about 100° C. Water with the oxygen-16 atom replaced by an oxygen-18 atom has a slightly higher boiling point. This means that heavy oxygen water evaporates less readily but precipitates more readily than does normal water.
This in turn means that the fraction of oxygen 18 versus oxygen 16 in the water and air bubbles in the ancient ice in Greenland and Antarctica are indicative of the climate at the time that that ice and those air bubbles formed. Despite being a half a world apart, the ratios of oxygen-18 to oxygen-16 over time are highly consistent between Greenland and Antarctica. The consistency of these measures at half a world apart are almost universally taken as being a proxy for something else, and that something else is climate.
There are many other proxies for past climate. There are other isotopes that serve as proxies. The amounts and kinds of pollen in mountain glaciers and ice sheets form yet another kind of proxy. The kinds of plants that do grow in some locales and how fast they do grow is highly temperature dependent. Like ice, buried muds in the oceans also show variations in various proxies. Climate scientists put these proxy measurements together to arrive at the temperatures from 2000 years ago, and even further into the past.


Least populated time-zones What are there any loneliest places on earth in term of population per time-zone? What is the answer for full hour time-zones (UTC+1,UTC+2..) and in other including for example UTC+4:30?

SORRY
I may have actually meant, what is the loneliest time? When is the least amount of people awake (perhaps even including rare cycles; eclipses, solar minimums, etc)?

Thus, meaning that if you lived in the right place, at the right time, you would be one of the loneliest men on Earth.

There is one timezone that is completely uninhabited: the UTC-12:00. It covers only two islands: Baker Island and Howland Island that are both uninhabited (owned by US). Because of the weird way timezones are divided in the pacific there are timezones that practically use the same time (e.g. UTC+12 and UTC-12), but are actually in two different days. However if you strictly interpret the question no-one is lonely here as there is no-one here, so this might not comply.

The second least population is at UTC+08:45 that covers village of Eucla and other villages in Australia with a population of around 200. The area is surrounded by signs to remind you to turn your clocks, but it is unofficial so it might not comply either.

The third least population is at UTC+10:30 that covers an island called the Lord Howe Island that belongs to Australia and inhabits 382 people. If you don't accept timezones that aren't in integer changes from UTC then this UTC+10:30 might not satisfy your curiosity.

The first full integer timezone shift from UTC (that has any population) is UTC-02:00 that consists of Atlantic islands of Brazil like Fernando de Noronha, Trindade, Martim Vaz etc. Also South Georgia and South Sandwich Islands of UK belong in this timezone. The total population then is somewhere around 2700 people. Unfortunately these are the places that use this timezone all year round and other areas like densely populated Brazilian cities use this timezone as daylight saving during their summer increasing the population drastically so even this timezone might not satisfy your criteria.

Finally UTC-11:00 being full integer change from UTC, with only all year round usage (isn't a daylight saving timezone for anyplace) consists of American Samoa, Midway Atoll, Jarvis Island and Palmyra Atoll of US and Niue of New Zealand and has under 60000 inhabitants.

Ps. The estimated population numbers are from the wikipedia pages of the locations mentioned.


What causes waves to form the characteristic "breaking" shape as they approach the shoreline? We all know that as waves approach the shallow shores, the waves begin to form a characteristic shape.  The upper portion of these breaking waves appears to curl forward and downwards over the bottom segment of the wave, before breaking into "white wash". The image below illustrates what this characteristic shape looks like:

So why do waves form this characteristic breaking shape as they approach the shallow shores?

The physical process you describe is known as wave shoaling.

At the basic level, waves propagating into shallow water become shorter and higher, and consequently, steeper. In shallow water, the water particles near the crest move forward faster than those below them. Similarly, the particles near the trough move backward faster than those above them. This causes strong shearing of the near-surface body of water, eventually forming a plunging breaker, or a surf wave. For small-slope (linear) and inviscid (no friction) waves, the above is a consequence of the bottom boundary condition for the water velocity to be zero at the sea floor.

There are two fundamental and related properties of water waves that contribute to shoaling. One is the wave frequency $\omega$ remaining constant as the depth $d$ decreases. Think of this as the conservation of wave crests at any fixed point. However, the wavenumber $k$ (wavelength $\lambda$) must increase (decrease) with decreasing depth, as per the dispersion relationship of water waves (neglecting the effects of viscosity):

$$\omega^{2} = gk\tanh{(kd)}$$

where $g$ is gravitational acceleration. In shallow water, the dispersion relationship reduces to:

$$\omega = \sqrt{gd}k $$

and phase speed $C_p$ and group velocity $C_g$ are both proportional to the square root of the water depth:

$$ C_p = \dfrac{\omega}{k} = \sqrt{gd} $$

$$ C_g = \dfrac{\partial\omega}{\partial k} = \sqrt{gd} $$

Individual wave crests propagate with phase speed $C_p$. Wave groups and wave energy propagate with group velocity $C_g$. Thus, waves entering shallow water become shorter and slower. The second important property leading to shoaling is the conservation of wave energy flux, which is proportional to the group velocity and wave energy:

$$\dfrac{\partial(C_{g}E)}{\partial x}=0$$

Because the group velocity decreases, the wave energy (read: height) must increase (locally). This causes the waves to grow in height as they enter shallow water. As pointed out by @IsopycnalOscillation in a comment above, the separation of water particles from the wave crests happen because the individual orbital velocities at the top of the crest exceed by far the phase speed of the wave.

Although bottom friction is significant and non-negligible in shallow water, it does not cause shoaling. Mathematically, wave shoaling can occur for completely inviscid and small-slope (linear) waves that propagate into water of decreasing depth.


Formation of flint & chert in limestones/chalk Chert and flint are commonly found in chalky deposits (and have obvious importance in human history as tools). What are the processes of diagenesis of these silica-rich nodules in otherwise silica-poor horizons?

This is not really my specialism, but in the absence of other answers so far, I'll give it a go.

Firstly, to simplify the terms of the question a little bit, flint is a form of chert, so we don't need to distinguish the two terms: we can just talk about chert in general. Also, I'll ignore chert beds formed in siliceous oozes, since you're specifically asking how cherts form in carbonate beds. Nichols (2009) gives a concise explanation, and I don't think I can do better than to quote it:

  Diagenetic cherts are formed by the replacement of other material such as calcium carbonate by waters rich in silica flowing through the rock. The source of the silica is mainly biogenic with the opaline silica of
  diatoms, radiolarian and siliceous sponges being redistributed. Chert formed in this way occurs as nodules within a rock, such as the dark flint nodules that are common within the Cretaceous Chalk, and as nodules and irregular layers within other limestones and mudstones.

If you want more detail, Maliva and Siever (1989) would probably be a good reference. (Free online reading for all, and download for many institutions, at the JSTOR page.) Here's the abstract:

  Mapping of carbonate dissolution in nodular chert-bearing strata indicates that nodular chert formation in a diverse suite of Phanerozoic limestones occurred in bulk pore waters that were at calcite saturation. Opal-CT and quartz supersaturation was achieved in most chert-bearing strata by the intraformational dissolution of amorphous silica skeletal material. Chertification occurred by a combination of force of crystallization-controlled replacement of the host carbonate, whereby non-hydrostatic stresses resulting from opal-CT and quartz crystal growth caused calcite dissolution, and the isomineralic heterogenous nucleation of new opal-CT and quartz crystal at nodule peripheries. The restriction of the solution phase at silica-carbonate contacts to thin films permitted the preservation of ghosts of micron-sized features in the chert. Heterogeneities in sediment organic matter content, porosity, and biogenic silica concentrations promote the nucleation of chert nodules in some formations.

Maliva, R. G., & Siever, R. (1989). Nodular chert formation in carbonate rocks. The Journal of Geology, 421‒433.
Nichols, G. (2009). Sedimentology and stratigraphy. John Wiley & Sons.


How have Farallon plates's remnants stayed as they were inside the mantle? Why hasn't the subduced Farallon Plate's materials been recycled? Why do they appear to be flowing in a molten state?

Rock is dense, is a good insulator, and usually has very high specific heat capacity; the crust is also kilometers thick. The combination of these qualities means that it takes a very long time, even geologically speaking, for crustal blocks to melt completely in the mantle. This is exacerbated by the fact that the mantle, especially the shallow layers close to the crust, is not actually much hotter than the melting point of most of the minerals in the rocks.

The reason that the crust is still visible in seismic wave variances while it moves in an apparently molten fashion is that even though it hasn't been completely melted it has been in the mantle long enough to reach a uniform high temperature, high enough to become plastic and flexible. So it still presents as a density anomaly because its not yet as molten as the material around it but it will flow, if slowly, because it is semi-molten, similar to the asthenosphere.


Paleogeographic atlas software I am looking for a paleogeographic atlas software, like the one used here at min 10:15: you can navigate through the ages with an arrow and visualize a reconstruction of the geographic features of any area of the world in a certain age:

Has anyone got any suggestion? I use Linux (Debian) but I'm interested in software for any operating system.

I haven't seen the video you linked to, but from personal experience GPlates is pretty good.  It's open-source and runs on Windows, Linux and MacOS X.


How does the meridional overturning circulation affect sedimentation rates in the North Atlantic? There's a lot of downwelling in the region. Does this increase sedimentation rates?

Downwelling speeds in the deep water formation areas are likely not significant when compared with the settling speeds of most sediment particles. While deep waters have clearly defined oxygen and nutrient characteristics, it does not seem likely that they can have a particular sedimentary character.

The deep water circulation associated with the meridional overturning circulation (MOC), while not very intense (a few cm/s), can transport some of the finer sediment classes along with it.

The main sedimentary signal is likely associated with calcium carbonate. The shutdown of the MOC could have significant effects on the CaCO3 balance (Chikamoto et al., 2008).


Seeking climate and related sciences textbook recommendations I will be starting a Master's program in data science soon and my eventual hope/goal is to do climate-related data science work. I did an independent study for one semester in college on the mathematics of climate and it inspired me to want to learn more and possibly pursue climate research as a career path. The two main textbooks I used for that class were Mathematics of Climate (Hans Kaper and Hans Engler) and Atmosphere, Ocean, and Climate Dynamics (John Marshall and R. Alan Plumb). My undergrad major was applied math, so my knowledge is limited mainly to content in those two books. In hopes of obtaining more background knowledge on environmental and climate sciences, I'm wondering if anyone can recommend textbooks that I could self-study before I start the program, so that I could potentially do a climate-related final project. I'm hoping to gain as wide a range of knowledge as I can during the next couple of months, so I welcome suggestions on anything (whether textbooks or other resources) that might be useful or just plain interesting! I will also mention that any books that include data assimilation would be superb. Thank you!

There are loads of books. I will refer you to one of my previous answers which can apply to the meteorological aspects of climate. An additional classic for climate is Physics of Climate by Peixoto and Oort.


What is the 'natural variation' in global temperature that climate-change skeptics mention? I was wondering if there really was some natural variation that keeps getting cited by climate-change skeptics that predicts a warming? The only such variation I can think of would be the milankovitch cycles, however this predicts cooling not warming at present (as far as I recall).

First off, let me preface this answer with a disclaimer: I do not deny climate change.

From what I've read, the skeptics for the most part don't claim to have an alternative explanation for the recent warming. Their arguments (not mine!) are fourfold:

The recent warming doesn't exist, is natural, or is just noise. The tiny half degree warming we've seen in the last 40 years is a tiny blip on the huge changes that have occurred in the past.
Climate change is a natural occurrence. The climate has changed historically naturally by huge amounts, much bigger than the tiny half degree warming we've seen in the last 40 years.
Predicting the weather after ten days is a fool's errand. Predicting climate is worse than a fool's errand. It can't be done.
Even if things have warmed up in the last forty years, one thing is certain: It's not CO2. That a tiny trace gas could possibly drive the climate is laughable.

Those are not my arguments.

With regard to point #1,

Source: World Meteorological Organization Press Release No. 976: 2001-2010, A Decade of Climate Extremes

The above image speaks for itself. The global temperature change over the last forty years is very real, and is not noise.

With regard to point #2, yes the climate has changed in the past, and by huge amounts. We've had everything from snowball Earth to dinosaurs roaming the Arctic. And the point is? This argument is akin to a farmer taking a trip to the Grand Canyon and upon seeing what damage nature can do decides to forgo contour plowing and other anti-erosion farming techniques.

That the farmer's field might turn into a mountain or be washed out to sea several millions of years from now is irrelevant. What's relevant is that his good or bad practices have an impact on the world food supply. That nature can do far worse does not negate those bad farming practices. Bad farming practices are bad for humanity.

Getting back to climate change, if higher global temperatures are bad for humanity, it doesn't matter matter one bit how close ice came to the equator or how far north dinosaurs roamed in the past. What matters is that modern humanity is sensitive to climate change, be it natural or induced by humans.

With regard to point #3, yes, weather becomes chaotic after ten days or so. That does not mean that climate is chaotic, and if it is, the ~ten day Lyapunov time of the weather does not mean that climate also has a ten day Lyapunov time.

With regard to point #4, it is CO2. It was amusing to follow the skeptic response to Richard Muller's Berkeley Earth Surface Temperature project. Muller was a self-proclaimed skeptic, and he was going to prove those leftist climatologists wrong. The skeptic community cheered at the start.
"He's going to prove them wrong!" A funny thing happened on the way to proving them wrong: He proved them to be correct. Muller was an honest scientist in this regard. His own work caused him to switch from being a skeptic to ascribing to AGW.