What would change if our earth lacks mountains? I just asked myself what is the role of the mountains on our planet earth? Well there's a well known role for the climate and weather.

But is there a kind of physical or geological role? What would happen if our earth lacks the mountains on it? Will we have more earth "Movements" (earthquakes, tectonics...) i suppose erosion will be much heavier then it is now. And therefore i suppose that human life in such a planet would be impossible.

In the Answers i would like to consider two scenarios:

Earth as we know but without mountains (mountains have never been
formed or don't exist at all)
What will happen if the Mountains would just been taken away?

Well i would like to get some kind of scientific answer from a geological point of view!

Well, mountains are not a cause. Mountains are an effect. It's not that we have earthquakes because we have mountains. We have mountains because we have earthquakes.

  Earth as we know but without mountains (mountains have never been formed or don't exist at all)

So by saying that mountains never existed at all, you are implying there are no tectonics. That would be a sad thing - one of the things that make Earth so alive and interesting is the fact that we have plate tectonics. Go and have a look on Mars, the Moon, etc. There are no active tectonics there are those are dead places.

  What will happen if the Mountains would just been taken away?

They would just form again. First of all, there would be the effect of isostatic rebound. When you take away a certain mass from an elastic thing, that thing bounces back up. When you're sleeping on your bed, there is a dent in it. When you get up, it springs right up. This will happen also in the Earth. It is happening actually as we speak - certain places in the world (Scandinavia is one example) that are slowly rising because the huge ice sheets that existed during the last ice age melted. That said, India is still colliding into Asia and the Mediterranean is still closing so you would get more Himalayas and Alps. Plates are still subducting so you you will get volcanic arcs such as the Andes or Japan. It will take some time, but the mountains will come back.


Can soil color give accurate data about properties which affect it? I understand that soil color is affected by several factors some of which are (but not limited to):

organic matter content
underlying parent material
drainage and aeration

Soil color being an indirect measure of other important characteristics (Foth, 1990), I have been thinking about building an application that reads a soil color in terms of it's hue, value, and chroma as the munsell color system using openCV color detection techniques.
After reading this data, the application should be able to interpret it to give meaningful information about the soil. This can be organic matter content, dominant minerals, drainage etc.
My questions now

What information be accurately be obtained from soil color?
Is this application by any means feasible?
Do technologies exist that achieve the same? (using computer vision)

Reference
Foth D. (1990). Fundamentals of soil science J Willey.

Unfortunately, the color itself won't give you much more information than the amount of organic matter and oxides/hydroxides. The amount of carbonate and some silicates might also be detected, but those values would be very vague without further examination of the soil.

If you want to get more information you would need some more data. The grain sizes for example (sand, clay, silt), pH-measurements, the amount of water and air, what other minerals and the salinity. You also need information about the soil biota, and so on. To collect all these data you need further research methods.
So your project idea is nice, but a picture alone won't bring you much information since the soil's properties are too complex.

Also writing such a program (I guess a mobile app?) will be hard since all cameras take different pictures under different lighting.. furthermore they all have a different processing of the pictures.
I'm not sure how computer vision could help since you'd need a special camera. So if you want to make an app you're going to have a hard time. I don't think you want to design a special device just for this.

Another aspect is that whenever you work with soil, you're going to get dirty. That's no good environment for such technology, that's why the munsell charts are used. It's no problem when they get dirty.

I really like the idea, but I don't think it'll get you far, but that's just my opinion!


How can scientists measure chemical composition on other planets? How can scientists measure chemical composition (oxygen, nitrogen etc) and temperature on other planets without being there?

Scientists can measure the chemical composition of the atmosphere of other planets using spectroscopy.  Each molecule in the atmosphere absorbs and re-radiates at specific frequencies of light that are a function of temperature and unique to the specific type of molecule.  For more information see https://en.wikipedia.org/wiki/Extraterrestrial_atmosphere and http://www.physics.uu.se/research/astronomy-and-space-physics/research/planets/exoplanet-atmospheres/ .


What are the risks of developing geoengineering? Wikipedia page for geoengineering entry list a lot of proposals to decrease global temperature:

Solar radiation management methods[5] may include:

Surface-based: for example, surface-based mirror infrastructures,[29]    protecting or expanding polar sea ice and
glaciers, including the use    of insulating blankets or artificial
snow,[30][31] using pale-colors    for roofing materials and other
man-made surfaces (i.e. roadways and    exterior paints), attempting
to change the oceans' brightness,    growing high-albedo crops, or by
distributing hollow glass beads in    selected areas to increase ice
coverage and lower temperatures.[32]
Troposphere-based: for example, marine cloud brightening, which would    spray fine sea water to whiten clouds and thus increase cloud
reflectivity.
Upper atmosphere-based: creating reflective aerosols,    such as    stratospheric sulfate aerosols, specifically designed
self-levitating aerosols,[33] or other substances.
Space-based: space    sunshade – obstructing solar radiation with    space-based mirrors,    dust,[34] etc.

Carbon dioxide removal

Creating biochar (i.e. in biomass-fired thermal power plants), for    mixing into the soil to create terra preta
Bio-energy with carbon capture and storage to sequester carbon and    simultaneously provide energy Carbon air capture to remove carbon
dioxide from ambient air
Afforestation, reforestation and forest restoration to absorb carbon    dioxide
Ocean afforestation and ocean fertilization (which includes iron    fertilization of the oceans)

Why have none of these methods been implemented?
What are the risks of developing geoengineering?

We don't know, and that's why we have to develop it.
that's the thing about undeveloped sciences we don't know what many of the risks are, Its a case of knowing what we don't know. Which is one big reason to develop it, so we don't cause harm accidentally.
Lets be clear we already are geoengineering right now, by driving cars, changing the landscape, polluting the air,  we are just doing it blind. We have to research things to understand the risks, and geoengineering has barely be scratched.


What is the intensity of terrestrial radiation? I wanted to know  what's is the intensity of terrestrial radiation? I mean the long wave radiation emitted by Earth & its atmosphere. As, I was differentiating between solar radiation and terrestrial radiation and intensity is the major thing to know when differentiating between these.

Assuming your question is about how much of the sun's radiation hits the Earth's surface rather than just reaching the edge of the atmosphere ...

The amount of solar radiation that hit's the Earth's surface varies a lot, depending on weather conditions, time of day, day of the year, latitude, altitude, air quality ... It can be anywhere between 0 and ~$1200W/m^2$

There is a standard "full sun" solar intensity which is used as a benchmark for things like photovoltaics testing and calibration. That's $1000W/m^2$, with an atmospheric spectrum denoted by AM1.5


How to measure the cycles of earth moving/rotation? My knowledge of science is very basic, but after some research I have some knowledge, but I am still not clear with so many things regarding to this earth.

I have read Laser's Measure the Earth's Rotation and Wobble but would appreciate it if anyone who knows science well, could explain how the rotation of the Earth is measured and how it is affected by the Chandler wobble and the annual wobble?

In theory, if the Earth was a solid object, the Chandler wobble would be easy to understand. It's simply a result of the polhode rolling without slipping on the herpolhode lying in the invariable plane. In other words, $\mathrm I \dot \omega + \omega \times (\mathrm I \omega) = 0$, where $\mathrm I$ is the Earth's inertia tensor and $\omega$ is the Earth's angular velocity. The Chandler wobble is simply the consequence of the Earth not having a spherical mass distribution and the Earth not having it's angular momentum and angular velocity coaligned.

In practice, the Earth is not a solid object. The theory behind the Earth's orientation is rather (putting it mildly) complex. The best model involves over a thousand parameters. Unfortunately, this best model of the Earth's precession, nutation, and rotation does not explain the Earth's orientation. The Chandler wobble, along with a number of lesser phenomena, is an after-the-fact discrepancy between the very best analytic model and the very best observational results.

Knowing the Earth's orientation is extremely important to some sciences, high resolution astronomy in particular. The US Naval Observatory (USNO) publishes its estimates of the deviation of the Earth's true orientation versus that of the best analytic models on a daily basis. The USNO is a key member of the International Earth Rotation and Reference Systems (IERS, for short, and yes, the acronym doesn't work. It used to work.)


If the earth were completely smooth and covered in water, what would occur with ocean waves? Related to this post: If the Earth were a smooth spheroid, how deep would the ocean be?

Consider ocean waves in the middle of a large ocean. They are being powered by the wind, but also lose energy due to viscosity, breaking and similar factors. Since the timescale for a wave changing is much smaller than the timescale of it crossing an ocean, for all practical purposes they already experience an infinite ocean.

A featureless ocean world would presumably have many somewhat constant wind systems that could add a lot of energy to wave motion, but with an absence of shores to break on these energetic waves will just keep on going with an amplitude where the average energy gained and lost are equal. Since even a powerful tsunami is nearly invisible in deep water, the ocean world would look relatively calm with merely a lot of ocean swell.


How does the pole-to-equator temperature gradient scale with height contours? Are the pole-to-equator temperature gradients lower at higher heights than at lower heights (like 850 mb/500 mb)?

If so, why is it the case? Especially given that the zonal circulation tends to be much higher at higher heights, so one could expect there to be less meridional heat transport.

(Bonus question: how is it different in other planetary atmospheres?)

It depends on the season. The figures below shows zonal mean temperature for June-July-August from ECMWF ERA-40 reanalysis.  As you can see, at 100 hPa, the equator is actually colder than the sunlit hemisphere.

June-July-August

December-January-February

For getting the "facts" on this kind of questions, the ECMWF ERA-40 atlas is a good source.  Now as to why this is the case; that is a much more involved question on atmospheric dynamics and circulation.  The Earth heats the surface, in particular where it's sunlit.  It also heats the spring and summer stratosphere, where ozone absorbs solar radiation.  Heating causes air to rise from the surface to the tropopause, where it's forced poleward creating a Hadley cell.  Meanwhile, the Earth rotates and everything becomes a highly chaotic and dynamical system.  So the fact that winds are strongest near the tropopause (see, for example, DJF winds) is not a direct consequence of where the heating occurs, but rather the effect of a lot of dynamics.

For further reading on why atmospheric circulation is as it is, one needs to study textbooks.  Some famous textbooks on dynamic meteorology and atmospheric science are:

James Holton, An Introduction to Dynamic Meteorology
Wallace & Hobbs, Atmospheric Science: An Introductory Survey


Could saltwater be useful for greening deserts and sequestering CO2? Desert greening is the conversion of deserts into moister environments with more vegetation. This could be used to combat desertification and (by sequestering CO2) climate change, and also to increase the amount of arable land.

(Image from the Wikipedia article on desert greening; credit to Mike Baird)
This obviously requires a water source. One potential water source (mentioned in the previously linked page under the "Water" section) is seawater (or other saltwater, e.g. from saltwater aquifers), which can be used directly by halophytic plants. 97.5% of Earth's water is saltwater, making this more abundant by far than freshwater. Using saltwater for irrigation is already being done in saline agriculture.
This method would avoid conflicts with use of freshwater (an increasingly scarce resource) and would be cheaper and less energy-consuming than using desalinated water. Mangroves and saltmarshes are more effective at sequestering CO2 than other types of ecosystems. And this would also have economic benefits if the plant species used have useful products like food, fibre etc.
How feasible is this idea? What challenges would this face? One challenge I can think of is the limited number of plant species able to grow on saltwater.

May the right aproach is, improve the process to turn saltwater into fresh water cause the only thing that i know which can be food and has salt tolerance is palm tree, mangrooves demmand a highly amount of seawater meeting a river


Could water pressure at the coast be the cause of continental drift? For example the Northern Africa is getting closer to Europe, where the depth of the sea is lower than in south African coast

Could it be that the water's pressure pushes the continent from where the sea is deeper?

Water pressure on both sides of the continent makes sure that all horizontal forces cancel out. So water pressure will not move a continent to the left or right because the pressure on the other side exerts the same force just in the opposite direction (assuming equal water depth). But the water pressure puts the continent under compression and will push the two sides of an ocean apart (putting the oceanic plate underneath under tension). In total, however, these forces are far too small to have any impact on plate tectonics.


What is the difference between a "flood" and a "flash flood"? Whenever weather warnings come up, I have heard of both a flood watch/warning and a flash flood watch/warning.

What is the difference between a "flood" and a "flash flood"? Are there any specific meteorological/weather forecasting patterns that distinguish one from the other?

Flood: An overflow of water onto normally dry land. The inundation of a normally dry area caused by rising water in an existing waterway,
  such as a river, stream, or drainage ditch. Ponding of water at or
  near the point where the rain fell. Flooding is a longer term event
  than flash flooding: it may last days or weeks.

  Flash flood: A flood caused by heavy or excessive rainfall in a short period of time, generally less than 6 hours. Flash floods are
  usually characterized by raging torrents after heavy rains that rip
  through river beds, urban streets, or mountain canyons sweeping
  everything before them. They can occur within minutes or a few hours
  of excessive rainfall. They can also occur even if no rain has fallen,
  for instance after a levee or dam has failed, or after a sudden
  release of water by a debris or ice jam.

  Source: National Weather Service Weather Forecast Office


Why do tectonic plates have a tendency to drift closer to the equator? There are many factors that drive the movement of tectonic plates on the surface of asthenosphere, and some of these factors have a larger contribution than others (e.g. slab suction).

One driving factor of less significance influencing tectonic plate movement is however the Earth's rotation. Apparently one such effect of the Earth's rotation is the "Pole flight force" which results in an equatorial drift of the plates to the equator.

Why does the rotation of Earth result in tectonic plates having a tendency to want to move closer to the equator?

I'm not a tectonicist or a science historian, but as far as I know the ‘pole flight force’ or Polfluchtkraft was introduced by Wegener in his theory of continental drift. Essentially it's just the application of centrifugal force to continents (or, if we are now considering it within the plate tectonic paradigm, to plates). As stated in the Wikipedia article you link to, this force is far too weak to account for plate motions, and this very fact was one of the reasons for the scientific community's rejection of continental drift. Modern tectonics doesn't seem to consider it even as a measurable contributing factor. The only modern references I've found to it have been in historical contexts, such as in Krause (2007). The subtitle of this paper, ‘Vergessene Begriffe der Geologiegeschichte’, translates to ‘forgotten concepts of geological history’, and as far as I can tell this is an accurate summary of Polflucht's current status.

Krause, R.A., 2007. Die Polfluchtkraft: Der LELY-Versuch
– Vergessene Begriffe der Geologiegeschichte. Polarforschung 76 (3), 133–140. DOI: 10013/epic.29962


Why does the colour of Earths oceans vary? Why does the colour of Earths oceans vary? Coast lines around the world appear to have different shades of blue.  The further one travels from the equator north or south the deep blue the ocean becomes. Is this effect a result of ocean temperature or salinity?

The color of the ocean water does indeed vary depending on the chemical composition of the water. In addition, the color of the ocean in satellite images is affected by the position of the satellite, angel of the sun, and weather.

Color of water in general

Water appears blue because long wavelengths (red or yellow light) are absorbed more efficiently in water than short (blue or green) wavelengths. Therefore, when a water body — in a swimming pool, for example — is illuminated by a white light source (the sun) the light that scatters back from the water tends to be blue rather than red.

The color of the water can further be altered by its chemical composition. In nature, the apparent color of water also depends on the light source, that is, the weather. The same ocean can appear very different in bright sunlight and on a cloudy, stormy day.

Color depends on substances in the water

The color of the ocean water can be greatly altered by substances dissolved or suspended in the water.
Typical substances that affect the color are chlorophyll (from waterborne algae) that make water appear green, or suspended particulate matter, such as silts and clay, that cause yellow or brown color. These are clearly seen in coastal areas, where local plankton blooms can turn water bright green, or river plumes carrying a high concentration of suspended particulate matter can be clearly identified from their brown waters. Other substances can alter the color of water as well. Colored dissolved organic matter (CDOM) related to decaying detritus, can turn water yellowish or green, for example. Water temperature and salinity themselves do not significantly affect the color of the water.

The color of the ocean, therefore, does depend on the location. For example, waters in areas with high primary production tend to be more green.

Color of oceans in satellite images

In satellite images, the color of the ocean can be influenced by the relative angle of the sun and the satellite versus the ocean surface. The ocean can appear darker if the satellite is at an oblique angle with respect to the ocean surface and/or if the sun is shining from an acute angle. In the case of geostationary satellites, the ocean near the equator can therefore appear to be brighter than in the high latitudes.

Moreover, the color of oceans may be affected by the surface roughness. Surface waves affect the way light is reflected and refracted in the surface and may cause the ocean to appear darker.

Consequently, the color of oceans may vary greatly in satellite images due to the track of the satellite and local weather conditions. This is often visible in large composite images, made out of multiple satellite tracks, where the ocean may appear patchy with different colors.


To what extent is hydroelectric power really renewable? One of the more widespread "renewable" ways of generating power is by harnessing hydropower, i.e. by exploiting the movement of falling or flowing water. Some of the most commonly seen implementations are river dams and tidal power stations.

All hydroelectric power stations obviously remove some kinetic energy from the water, usually by requiring it to turn a turbine. What I'm curious about is whether the removal of this energy is actually sustainable, i.e. whether energy is introduced back into these bodies of water at such a rate that we don't need to worry about depleting our bodies of water of kinetic energy.

Some might say that removing kinetic energy from the oceans on that scale is an obvious impossibility, but this strikes me as a foolish assumption in light of the dilution hypothesis, which clearly turned out false. Two-hundred years ago, people assumed that the oceans were so incredibly vast that man could never have an environmental impact on them. Today, here we stand, with oceanic acidification, warming, and overfishing being prime environmental concerns.

The exact same question and argument can be repeated for wind energy.

Do we have any idea exactly what the patterns and rates of energy transfer into our planet's water (and wind) systems are?

What are the potential environmental impacts of the large-scale removal of kinetic energy from our bodies of water?

(Note: among these environmental impacts, please don't focus on well-known impacts like damage to local ecosystems, loss of land, noise pollution, etc. I am chiefly interested in how this way of generating power affects our natural systems of energy storage and circulation, like oceanic and wind currents.)

The following question is off-topic, but it's a good follow-up: how is energy even introduced into our oceanic and wind current-systems? For example, I assume the moon's push-pull is responsible for the tidal movement of the oceans. What impact does the sun play? How fast is this entire system of energy transfer?

Comment: I strongly endorse the use of wind and hydropower as sources of energy over the further use of fossil fuels. However, I still think it is important to do research into the actual renewability of presumed-renewable energy sources, as we don't want to end up with another fossil fuel-type situation, in which we become aware of dependency on these energy sources and their malignant environmental side-effects long after widespread enthusiastic adoption.

Electricity from waves, from hydro (both run-of-river and storage) and from wind, are all indirect forms of solar power. Electricity from tides is different, and we can deal with that in a separate question. Global tidal electricity generation is not yet at the scale of gigawatts, so it's tiny for now.

Winds come about from the sun heating different parts of the planet at different rates, due to insolation angles, varying cloud cover, varying surface reflectivity, and varying specific heat of surface materials. Temperature differentials create wind currents.

Waves come about from wind, so they're a twice-indirect form of solar power.

Sunlight on water speeds up evaporation, lifting the water vapour into clouds, giving them lots of gravitational potential. That rain then falls, sometimes onto high land, from where it can be gathered into storage reservoirs that are tapped for electricity, or where it flows into rivers that are then harnessed in run-of-river hydro.

How much power is there? Well, the insolation from the sun is, at the outer boundary of the Earth's atmosphere, at an intensity of about 1400 Watts per square metre. The Earth's albedo is roughly about 30% - i.e. on average about 400 Watts are reflected back into space, giving an average irradiation into the Earth of about 1000 Watts per square metre. Picture the Earth's surface as seen from the Sun: wherever the Earth is in its orbit on its own axis, and around the Sun, the Sun sees a disc that has the Earth's diameter, so the surface area exposed to the Sun is just $\pi$ times the square of Earth's radius, which is about 6 300 kilometres.

So the incoming solar radiation is $1000 \times 6,300,000^2 \times \pi \approx 125 \times 10^{15} \rm \ W$

Current human consumption of non-food energy is about 17 TW, i.e. $17 \times 10^{12} \rm \ W$, which is about four orders of magnitude smaller than insolation.

There is an interesting open academic discussion (see "modelling methodology smackdown" section) about how much energy we can physically extract from wind: some models say it's only a few times as much as all the energy we currently use; others say it's another order of magnitude more again. Either way, it's way more than we need, so while it's an interesting modelling discussion, the answer wouldn't change anything right now.

There are also open academic discussions about the impact of removing terawatts of wind energy, on regional climates. However, regional climates are already one of the more uncertain parts of long-term climate forecasts; add to that the high uncertainties around where the energy extraction would be, and what the specific effects of extraction are, and we end up with a lot of speculation and very little usable information. Not that this has prevented people from trying to model it, and reporting their results: but the uncertainties dwarf the results.

And harnessing renewables doesn't change anything significant in the Earth's total heat budget either, because almost all of that $1000\ \mathrm{W/m^2}$ from the sun already ends up as low-grade heat anyway. If harnessed for electricity, that electricity will then get used, and almost all of it will then end up as low-grade heat. The bit that will change when we get close to 100% renewables is that we will no longer be injecting about 15 TW of energy from fossil and nuclear into the biosphere (2 TW is renewables). But that's only about 0.01% of the insolation anyway.


How much warming there was over time for a specific month? I'm calculating warming trends in specific places and periods of time, that are related to the time a migratory bird spends in a stopover. But using different methods I got different results and I'm trying to figure out which is the most accurate. I know it will depend on location, so my sites are Southeast Canada and the Arctic. How much warming is possible in 40 years for example in a period covering only one month in spring, like May? What would be a good value to compare my results? spring temperature warming trend?

There's a lot of fluctuation in temperatures, so when averaging them I get no changes, including in the Arctic, which cannot be true. I looked at trends of the maximum temperatures and they are increasing, also investigated the anomalies, but I would like to have an advice.

It is hard  to help unless you clarify what methods have you tried. However, I would suggest to explore reanalysis weather models, as they are the most accurate source of estimated weather conditions worldwide in the past.

A recommended reanalysis is ERA-interim, starting in 1979 so it gives you  39 years, if you really need 40 you can use JRA-55 that starts on 1955.

The KNMI Climate Explorer is a great way to retrieve and plot data from those models.

If you get in there you can set it to plot monthly mean temperatures for a given location. Here is an example of somewhere in SW Canada:

That will produce a plot like this:

Were you can click the "raw data" to get the raw values, and that will produce an output like this:

Where each row is a year and each column is a month. So you can pick the column of the month of your interest and compute the trend from that.

Does it makes sense?


Is there any case that changed from earthquake safe zone to danger zone? Is there any case that changed from earthquake safe zone to danger zone? As plates move, I think that earthquakes belt will change over time. But is there really a case in which the earthquake-safe zone was replaced by an earthquake-prone region for such a shift or for any other reason?
 Or is there a region that is predicted to be an earthquake hazard zone in the future?

Yes, prior to 1983, central Idaho was classified low to moderate.  On October 28, 1983,  a  powerful earthquake occurred in Lost River Range at Borah Peak in central Idaho. The shock measured 6.9 on the moment magnitude scale and had a maximum Mercalli intensity of IX (Violent).

The earthquake was centered only 50 miles from a Idaho National Engineering Lab (nuclear research laboratory), but no damage was reported a the site.

Unfortunately, I can't find an internet accessible report but I remember discussing this earthquake at length in a Engineering Geology class I was taking in 1986.  The magnitude of the Borah Peak surprised the US government prompted the USGS to reclassify earthquake hazard zones in Idaho and Utah.

Location of Borah Peak, Idaho.

Current quake hazard map (from USGS:)

References:

Wikipedia Borah Peak.
New York Times article on quake
Geological summary of the quake: Idaho State University By, Steven W. Moore, Geologist and R. David Hovland, Geologist:


What is the origin of cleating in coal? Why do some coals show cleating and some not? Is cleating in coal related to coal's plant source or depositional process or post depositional processes?

Short answer, its not well studied. It is most likely a diagenic process just because that is the source of most fractures in rock.

https://www.sciencedirect.com/science/article/abs/pii/S0166516297000128

https://www.sciencedirect.com/science/article/pii/S1674775514000341


Why is it good scientific practice to 'build' a 'control Earth' from models, and where else do we 'build' controls? Usually, when data is collected in an experiment, scientists have a control. Experiments are seen as flawed without controls. I am just curious as to where else scientists have 'built' controls using models. Obviously, we cannot find a real 'control Earth', so we must make climate models, but then why can we even proceed with the experiment (how are we so sure the models act within a small error of the 'control Earth')?

It's true that, usually, when data is collected in an experiment scientists have a control, and very often not having a control results in a flawed experiment - that is, an experiment from which less conclusions can be drawn.

Experiments are a very efficient way to gather high quality data, but in some fields they might even be impossible. However, experiments aren't the only way to get knowledge and they aren't mandatory to make science.

In some fields experiments are quite easy and therefore most research is based in experiments. For example, it's usually easy for chemist to test the way substances react by making experiments.

In other fields some questions can't be resolved by direct experiments due to practical or ethical reasons. In a known textbook example, sociologists are interested in what circumstances cause suicide rates to rise or drop, but ethics prevents them from performing an experiment by submitting a sample of people to circumstances supposed to induce suicide and compare suicide rate of this sample with suicide rate in a control sample. Therefore, sociologist need to draw conclusions from observational data - that is, observing real population under natural circumstances they can't adjust - or from experiments of related phenomena that can be performed without ethical concerns.

We in Earth sciences face a similar problem: some experiments can't be done because of scale or just because we just have an only Earth. For example, how do we know that rivers cause deltas? Ideally, we'd like to do an experiment by selecting several coast tracts, putting rivers in a randomly chosen sample of them, waiting a few millions of years and comparing evolution of the coast tracts with and without rivers. We can't do this experiment, but it doesn't prevent geologists to have learned a lot about deltas, because we have a lot of data from observation of naturally occurring deltas, from small scale experiments, and from study of auxiliary sciences (physics, hydraulics, etc.).

Climate is similar to deltas. Just as we can experiment with setting and removing rivers, we can't change CO2 levels of the whole atmosphere to measure what happens, but we can observe what actually happens, search for geological register of what happened in the past, do a lot of small scale experiments, and use our knowledge of basic sciences and draw conclusions about climate evolution from them.

Clearly, interpretation of that data is not as straightforward as data from a big experiment would be, but it is still possible and useful. In fact, it's the way most of current knowledge in many fields has been built.

All that without needing a random sample of Earths nor a control Earth.


Is this graph showing the average temperature on Earth going back millions of years accurate? Looking for a historic record of the average temperature on Earth going back millions of years, and this 2002 graphic the from the PALEOMAP Project is currently the best I am able to find. Is it accurate, and if so, why? If it is not accurate, is there a graph that is?

In a word, no.

The graph is based on work by Chris Scotese. The climate science site RealClimate.org has this to say about it:

  Scotese is an expert in reconstructions of continental positions through time and in creating his ‘temperature reconstruction’ he is basically following an old-fashioned idea (best exemplified by Frakes et al’s 1992 textbook) that the planet has two long-term stable equilibria (‘warm’ or ‘cool’) which it has oscillated between over geologic history. This kind of heuristic reconstruction comes from the qualitative geological record which gives indications of glaciations and hothouses, but is not really adequate for quantitative reconstructions of global mean temperatures. Over the last few decades, much better geochemical proxy compilations with better dating have appeared (for instance, Royer et al (2004)) and the idea that there are only two long-term climate states has long fallen by the wayside.

and

  Some better examples of long term climate change graphics do exist. This one from Veizer et al (2000) for instance (as rendered by Robert Rohde):

For a more detailed discussion of graphical reconstructions, see this RealClimate entry


How does soil fertility differ between Scandinavia and Russia How is climate and soil fertility different in Scandinavia comparing to Russian territory of 1500s? Did Scandinavia have more favorable climate and more of arable and higher yielding soil than Russia of 1500s did?

I don't know much about Scandinavia in the 1500's, and in particular, how much was forested. However, one can say that the whole area was previously glaciated, with much of the topsoil being eroded away by ice, so soils generally tend to be thin, immature, sandy and nutrient poor. We do know that conifers predominated, leaving a soil-litter of pine needles. This latter has a high cation exchange capacity that leads to acid flushes whenever it rains after a long dry period. This acidity tends to leach out nutrients and adds small concentrations of toxic metals. These conditions do not help the soil's fertility. In addition, the valley floors often accumulate peat, hence high organic carbon and acidity.
The geology of Scandinavia is complex, and difficult to generalize. Periglacial outwash in Sweden and Denmark would have given rise to some fertile areas, especially where there is limestone to counteract the tendency to acidity. So compared to Russia, Scandinavian soil and agricultural potential is more variable.
As regards climate, coastal Norway is much warmer than either eastern Scandinavia and Russia on account of proximity to the Gulf Stream Drift. It also has higher rainfall, so the effective growing season is longer. Northern Scandinavia and Russia have close to 24 hours sunlight per day in high summer, so one wonders whether two growing seasons per year for some crops might be feasible? Are there any agronomists out there who can advise on this question?


What formed this rock slide formation near Hyndman Peak Idaho (photos)? While hiking Hyndman Peak in Idaho a couple weeks ago we noticed a rock slide that appeared to be formed by a glacier, however it was on the west side of the mountain. It was also strange that the downhill face was fairly sharp and was dirt/gravel instead of large rock. I only have a few smokey photos, and the satellite image is pretty poor, but just curious if anyone had any ideas.
Location in google maps

It is a normal rock slide, AKA a landslide, they happen all the time.

If a slope is not stable the rock collapses, landslides are very common and can be triggered by almost anything from rain, to imperceptible quakes, to simple erosion.
It could be rotational or translational the two blur together anyway. Most likely just a shallow rotational landslide.
The lower areas of a mountain being made of debris is extremely common, it is called a Scree slope. Where do you think all the rock that is eroded off the upper portions go?


How to calculate the kinetic energy spectra from ocean current timeseries? How does one practically compute the kinetic energy spectra from a timeseries of u- and v- Cartesian components of ocean current velocity ($m s^{-1}$) obtained from an Acoustic Doppler Current Profiler (ADCP) moored on the seabed?

Do you:

1) compute the spectra of each u- and v- components and then calculate the resulting kinetic energy from the spectra in the frequency domain? i.e. $KE(f) = 0.5\times(u_{(f)}^2 + v_{(f)}^2)$; where $KE_{(f)}$ is the kinetic energy spectrum per unit frequency and similarly $u_{(f)}$ and $v_{(f)}$ are the u- and v- power spectra?

or;

2) compute the kinetic energy $KE = 0.5\times(u_{(t)}^2 + v_{(t)}^2)$, where $u_{(t)}$ & $v_{(t)}$ are the current velocity timeseries and then calculate the power spectral density (i.e. using Matlab's pwelch) of the resulting KE?

Any guidance with the theory or practical calculation would be very much appreciated.

Thank you.

Do you get much different results if you do both ways?

I think if you want the kinetic energy spectrum, use your second method. Some separately compute velocity and KE spectra, e.g., figure 2 of http://journals.ametsoc.org/doi/pdf/10.1175/2009JPO4330.1 (DP Wang et al, JPO, Apr 2010). Comparing velocity and KE spectra, the KE spectra looks similar to the more powerful velocity spectrum, especially at low frequencies.

Others use your first method (e.g., http://journals.ametsoc.org/doi/pdf/10.1175/JPO-D-15-0087.1, Rocha et al, JPO, Feb 2016)


Why are there no mountains higher than ~10 km? Mars have several mountains above 10 km, with the highest being around 22 km (full list for Solar System here). Same for Io, Jupiter's moon. In contrast, the Earth has no mountain higher than 10.2 km (Manua Kea and Manua Loa, when considered from the bottom  of the ocean, more comparable with mars and Io), with the Everest being 8.8 km above sea level.

Is there any restriction in terms of the geological nature of Earth, or perhaps due to the atmosphere (e.g. water cycle/erosion), or closeness to the Sun (Mercury and Venus have even smaller mountains), that doesn't allow for higher mountains on Earth? Or is it perhaps just a matter of age? (in the sense that future tectonic movements will lead to higher mountains, without a particular limit)

More generally, is there any physical limit about how high mountains on this planet can ever be?

The reason mountains are higher on Mars than on Earth is the lower gravity on Mars, which is only one third of Earth gravity. Mountains are very heavy things, and on Earth the forces that build them have to fight against gravity, which is constantly trying to drag them down. For the same reason, small asteroids are usually not spherical, because they don't have enough gravity to even out the bumps, but when they get to about the size of Ceres, which is 500 miles in diameter, they do. Ceres is spherical. Mountains like Mauna Kea which have a large part under water don't count, because although mountains are heavy things they still have buoyancy and the sea is taking part of their weight. Venus has slightly less gravity than Earth, but because of the enormous heat is also more plastic, so this would mitigate against the building of very high mountains.


If North America were in the southern hemisphere, would the mountains and high desert have to be -east- of Tornado Alley? I've been trying to collate the reasons why Tornado Alley in North America is what it is. So far, I have the following:

The continental landmass is in the mid-latitudes (where the polar jet has the greatest amount of influence).
There are no geographic barriers, like bodies of water or mountains, between the North Pole and the rest of the NA landmass. Australia, New Zealand, South Africa (and Argentina for the most part) are separated from the South Pole/Antarctica by water.There's not much in the way of cold polar air dipping down as far south as the Florida Panhandle if there's a deep enough trough in the polar jet.
Sources of abundant heat and moisture at the surface. This primarily comes from the Gulf of Mexico, but there's also the Caribbean Sea, tropical Atlantic, plus the influence of the Gulf Stream and Bermuda High.
Large areas devoid of rough/rugged terrain. Besides the Appalachians and the Ozarks, there isn't a lot of mountainous terrain in the middle and eastern sections of the continent. The clash between tropical and polar air can continue undisrupted. In fact, the Appalachians can have the same funneling effect to tropical air that the Rockies have, shielding the Mid-Atlantic/Delmarva region while the Mid-South (sometimes even up to the Ohio River Valley) gets raked by tornadoes.
Mountains and high desert to the west. Warm, dry air coming off the High Plains in the leeward side of the Rockies and the High Plains in eastern New Mexico create westerlies at mid-levels. It acts as a lid, preventing surface moisture from rising. This is called a capping inversion, "cap" or elevated mixed layer. When the cap erodes, supercells can erupt.
Wind shear: Cold, dry northwest winds aloft; warm, dry westerlies at mid levels; and warm, moist air at the surface. Not only is wind direction changing with height, but wind speed as well (if there's a strong flow of moisture from the southeast, a "low level jet", then shear is further exacerbated).

But I wonder, what if North America were in the southern hemisphere? Would the mountains and high desert have to be situated on the eastern side of the continent to compensate? The predominant airflow in the northern hemisphere is west to east, due to Coriolis forces caused by the Earth's spin.

No, the mountains would still need to be west of tornado alley.

It all starts with temperatures.
You often hear the colloquial "warm\cold airmass battle" image.
But more specifically, the vital requirement for tornadoes is warm air advection.  Why?  Because warm advection fundamentally means the proper wind shear (cyclonic turning with height) for sustained storm rotation [for more info on why warm air advection is needed, look into thermal wind].
To have winds that bring warm air, you have to also have periods with cold air advection too.  Plus the oscillations between warm air and cold air give the potential for uneven vertical temperature profiles to develop, creating instability to fuel vigorous storms.  Warm air advection also builds the instability by transporting in that warm and moisture low level air.
And then fronts between warm advection zones and cold advection zones brings the trigger to best set off those ripe, unsettled conditions.  So on the warm sides of fronts is the prime location for supercells, though anywhere in warm advection has some potential.

Where do you find this battle of warm and cool air masses?
In the midlatitudes.  The most favorable tornadic regions have to be there, it's the only place with such regular oscillations.

And then the most favored spots within that band comes down to the positioning of mountains.
Mountains help pool the ingredients, and allow upslope flow to perhaps help kick off some of the storms.
But most importantly, mountain ranges perpendicular to the flow cause consistent lee troughing, the formation of surface lows downwind from the mountains when upper-level storm systems approach.

So it comes back to hich way the winds move in the upper levels of the troposphere in the midlatitudes.

And in the southern hemisphere, just as in the northern hemisphere, flow is mostly from the west at midlatitudes [for more on this, look into global or Hadley circulations, particularly the Ferrel cell].

So... indeed, we're talking east of mountains, since the wind is coming from the west.

Lee troughing is really important as young storm systems have strong meridional wind ahead of the system (bringing that juicy air in), the largest warm air region size near the low, and falling pressures, which further enhance low-level wind shear [look into isallobaric flow].  Areas further downstream (east) will have more mature systems with less warm advection collocated with instability.  That's a primary reason why the central US has more tornadoes than the eastern US.

Then it's all about large bodies of warm water to the right of the upper-level wind, such that it brings in that fuel in when a storm system starts to develop.  Because while warm advection is vital for the wind shear, you still need the moisture for tve precipitation (and to really ramp up instability).  The body of water needs to be warm (to evaporate lots of that water, and help that advection have that vital warming quality) and generally quite large (to provide lots of fuel regardless of slight wind differences, and do so regularly)

Finally, you did well to mention the high deserts\plateaus, as that is a pretty special ingredient to the Southern Plains.  As you may well know, a cap is a pocket of warm air aloft that prevents storm formation.  It's usually up around 850-600 mb, which is up a km or two.  High enough to be above  cloud base but low enough to counteract the nascent updraft energy... and also low enough to be driven by  ground features in other places.
That cap prevents widespread storms as you said, allowing a rotating storm to mature and persist.  It's a subtle ingredient in that you need just the right amount of it to keep excessive cells down, but not too much such that it prevents all storms.
It isn't nearly as vital as other features.  But it certainly helps.
And as you hinted, the best source for a cap is a dry hot elevated region upwind at that wind level (which works out to be to the southwest in the Northern Hemisphere... such that the cap in the southern Plains is primarily due to the Mexican mountains, and in the central Plains based more on the US desert southwest).
Even without such a region, there can still be natural capping from the mixed layer of the previous day, though.  And even widespread convection can be prolific at tornado producing if shear and instability are strong enough (see April 27th outbreak for instance).  So this isn't as critical as other ingredients.

So again, the order of most important to less important are:
1 - warm advection (= midlatitides, in spring\fall)
2 - Downwind of mountains (= east since midlat flow is from west)
3 - Warm moist water to right (south in NH, north in SH)
4 - Deserts upwind of capping level wind field (SW in NH, NW in SH)

The best spot is a reasonable balance between each ingredient, though still quite close to each source.
And that's all the Southern Plains of the US.  Out Oklahoma way.

One thing that actually turns out not to generally be as important is the geography in the cold air direction.  I've definitely heard that one suggested before, but don't see it factoring in much.
While the amount of land Poleward can help keep cold air drier and allow it to get colder perhaps overall, it's really not the strength of the cold air as much as the existence of it.  Too strong of cold and dry air and you'll have it reaching the warm water source, and disabling moisture return for long periods of time.
That's why tornado season in the US tends to peak a bit after warmth starts returning.
You can look at where prolific tornado areas are, too... the Great Plains have a lot of Poleward land; so does a lot of Eurasia, yet it's mostly unfavorable.
And then conversely, Australia doesn't have a lot of land Poleward yet is still a reasonably busy tornado spot.

Mountain ranges Poleward also generally aren't a big deal... even pretty large ones; one of the biggest tornado areas is Bangladesh\India, despite the disruption the Himalayas presents.  Because enough cold air can filter into the region in spite of the blockage.

The only thing that would be a real large scale geographic issue to the needed cold air would be a warm sea Poleward that modifies the incoming cold air significantly.
But that's pretty tough to have geographically.  Perhaps more possible in the Autumn... maybe the Great Lakes serves as a slight dampener on fall season tornadoes in parts of the US?  Though their effect is still mostly pretty small overall.  Bring too near any large body of water, in any direction, is really a downer on supercellular tornadoes, as it modifies temperature gradients and instability.

To your direct question... there actually is a very good example of what Tornado Alley would look like in the Southern Hemisphere already: the Pampas Lowlands of Argentina.
It has that big mountain range to the west, in the midlatitudes, and does have fairly warm water a ways northward.

But it doesn't have quite as large of a region east of the mountains to have the tornadoes in, the cold air (and storm system strength) is probably modified due to the closed nature of the Antarctic vortex and the widespread oceans of the SH modifying air masses, and the source water isn't probably as well located being so far north (and is it warm?).
But even still, Pampas area might be the second most consistent tornado region on Earth.  Such that some US storm chasers have traveled down there in our winter.

In the end, local effects play a huge role too, creating mesoscale ingredients (seabreezes\temperature boundaries, upsloping, local vortex flow, etc) to add plenty of rotation to the ledger (see Florida, one of highest tornadoes per square mile in US, in large part due to seabreeze water spouts and hurricanes).  But all things equal, being east of mountains in the midlatitudes is a jackpot ingredient to climatological tornado formation (regardless of hemisphere).


Why does the earth spin clockwise? Why does earth rotate in a clockwise direction?  Did a large meteor collide with earth causing earth to rotate?  If that is what happened, could another, larger meteor cause earth to reverse its rotation?

Earth's Spin

Earth rotating clockwise is the result of a chain reaction that started when Earth's star formed as the result gas clouds collapsing. During the collapse of the gas, one direction was shorter and a disc formed. Due to the law of conservation of angular momentum, the disc gained an overall spin, which was passed to all the objects of notable mass within its solar system; these objects are commonly known as planets. As a result, all planets within a given solar system have the same spin as the star in it to start. That said, the axis of a planet may do a 180-degree flip on its axis at some point, and if this happens, like Venus, it would spin counter to its native spin; in fact, in the case of Earth, it appears given there appears to be evidence that it's has flipped in the past, that the Earth's axis has already flipped at least twice, since it's current back in sync with the Sun's spin.

Might be worth noting that all rotating bodies that rotate clockwise when viewed from the southern hemisphere rotate and counter-clockwise when viewed from the northern hemisphere. Also, since the Sun is not solid on the surface, it does not rotate as a solid body; meaning it rotates faster at its equator and slower at its poles.

Earth's Axis

As for the reasoning behind, the axis of the rotation, as pointed out in other answers, this is the result of Earth's past impacts with objects of enough mass to produce the shift from a zero offset from the stars axis, to the current axis of the rotation. Future impacts would be able to change the rotation.

Will the Earth's axis flip?

  Scientists have found evidence that the Earth might have flipped over
  in the past, completely shifting the orientation of its poles. The
  theory has been around for years; that a large mountain range or
  supervolcano might unbalance the spinning Earth. Over the course of
  millions of years, the Earth would change the orientation of its axis
  until the object was balanced at the equator again.

Current Axis of the Planets in Earth's solar system


How do we apply CO2 sensitivity (3C ± 1.5C for every doubling) to current CO2 levels https://en.wikipedia.org/wiki/Climate_sensitivity#Estimating_climate_sensitivity

This indicates that current $\small\mathsf{CO_2}$ levels have a temperature equilibrium of 2.2 $\small\mathsf{^oC}$ disagreeing with statements that we are still below 1.5 $\small\mathsf{^o}$C. What did I do wrong?
280 PPM * 2 = 560 ppm
410 PPM / 560 ppm = 73%
73% * 3 $\small\mathsf{^o}$C = 2.2 $\small\mathsf{^o}$C

https://skepticalscience.com/climate-sensitivity-advanced.htm

You have done multiple things wrong here. One is that you have used a linear interpolation when you should have used a logarithmic interpolation. But that's a different question, one that you have already asked. I'll address that there. That said, a logarithmic interpolation would indicate that the warming due to a 73% increase would be 2.37 °C rather than 2.2 °C.

But that math is incorrect. We have not seen a 73% increase in $\text{CO}_2$ levels over preindustrial times. We have seen a 46.4% increase. The second thing you have done wrong is to incorrectly apply a linear interpolation. The correct value, assuming a linear interpolation is correct, is $\left(\frac{410-280}{560-280}\right)3^{\circ}$, or 1.39 °C.

We have seen more than a 1.39 °C increase from preindustrial times due to the 46.4% increase in $\text{CO}_2$ levels over preindustrial times. The correct math is a logarithmic interpolation: $\log_2\left(1+\frac{410-280}{560-280}\right)3^{\circ}$, or 1.65 °C.

We have not quite seen a 1.65 °C increase. So what's going on? Another thing you have done wrong is to implicitly assume that the current climate represents the steady-state response to the current $\text{CO}_2$ level. It does not.

Climate instead changes rather slowly. Suppose we stopped adding ever more $\text{CO}_2$ to the atmosphere but instead maintained $\text{CO}_2$ at the current level of 410 ppm. Temperatures will continue to rise for quite some time because the climate has not yet reached its steady-state response to the rather sudden rise from 280 ppm $\text{CO}_2$ to the current level of 410 ppm.


How can you explain this storm phenomenon? It's been a while since this happened, so I don't have many details. About 3 years ago, we had a popup storm here in Louisville. It was completely unexpected and unpredicted. That's not the strange part though. I took at look at the radar (it was about 5:00 PM) and noticed that on a 2 hour loop, the storm appeared as if it was brewing right over the city landfill and drifting towards the north-east. That was strange. They were essentially just thunderstorms with a lot of lightning, no tornado threat.

But then I zoomed out of the radar, and noticed that the same thing appeared to be happening over other nearby major cities (Cincinnati, Nashville, Indianapolis, St. Louis...). I'm not sure where the landfills are in those cities, but I'm guessing that may have been a pattern. That night was unusually muggy, like 100% humidity. The date was 7/20/2011.

(Click here for almanac data for area on that day)

What could explain this phenomenon?

This case is an excellent example of urban-induced convection.

Urban areas have very different surface and soil properties, leading to a different heat balance relative to more natural environments. At times when solar shortwave radiation forcing is high - summer time, early afternoons - urban areas act as heat islands. Sensible heat flux and outgoing longwave radiation are then increased relative to the environment. While latent heat fluxes are decreased because of lack of soil moisture and vegetation in the cities, there is enough moisture coming from the environment to trigger convective cloud formation and rainfall downwind from the urban area.

As to the question why did this occur in four urban areas at the seemingly similar time, it just happened so.

See this review article on urban-induced convection and associated physical processes for more details.


Why does halite have perfect cleavage at the (110) plane? Why doesn't it cleave nicely along the (100) or (010) or any other planes? What determines its cleavage plane? I know it has something to do with the fact that it crystallizes in face centered cubic  system but I don't understand why things happen the way they do.

I think the commenters have identified the issue. Halite does not have perfect cleavage along the {110} plane. As recorded in Mindat, Halite has perfect cleavage alone {100}, {010}, and {001}. This makes sense, as Halite is a cubic mineral (fcc), these are the planes you would expect it to cleave on.


Is evapotransporation accounted for in climate models? Is evapotransporation accounted for in climate models, or is it considered so insignificant that it's not considered?

Could additional crops being planted within the last 100 to 50 years account for additional moisture in the air now?

Sorry, here's some more background.  I recently attended a conference in which there were 2 speakers, one from NOAA and another from the USACE, that both came to the same conclusion that our atmosphere is becoming more 'wet'.  In particular the NOAA scientist compared the last 50 years to the fifty years prior to that.  So by comparing the last fifty years to the 50 years prior to that it looks like the atmosphere is becoming wetter.  I just wonder, if there were more crops in the ground in the last 50 years, what impact that would have on the climate becoming wetter.

I have done some googling on this matter and am finding mostly information on how a changing climate may effect evapotransporation but not vice versa.  I also checked out the USDA website for acres planted over time and I'm not finding much further back that a decade or so.

Now most models include changes in evapotranspiration, it is usually grouped together with a few other factors (like draining wetlands) under the heading "Land Usage"

Now the question does "Could additional crops being planted within the last 100 to 50 years account for additional moisture in the air now" the answer is no, not by itself.

To get more moisture into the air long term you need the air to be warmer, otherwise it just rains it out. Another issue is different crops affect evapotranspiration in different ways. For instance irrigation induced evapotranspiration, likely the largest evapotranspiration effect, may actually have a cooling effect, by increasing cloud cover and precipitation. Lastly land usage is only a small impact not counting the increased greenhouse gas emission it can cause.


Why does the salt in the oceans not sink to the bottom? This is something that just occurred to me. If heavier elements sink, then how can the entire ocean be salty? Shouldn't the 'salt', because of its density, all sink to the bottom of the ocean? In theory, only the deepest parts of the ocean should be salty, while the top of the ocean is not. Yet, the only water in the world that isn't salty comes from rain and rivers. How can this be?

When dissolved in water, salt breaks up into sodium and chlorine ions, which combine with water molecules so they cannot easily sink. However, there is a tendency for streams of fresh water to float on salt water and rise to the top. This caused problems for British submarines in the Dardanelles Straits during WW1. Moving from almost fresh water to the denser salt water, they suddenly became more buoyant and rose involuntarily to the surface, making them visible to Turkish gunners on the shore. There are also parts of the ocean where there are pools of very salty water lying on the bottom in such a way as to clearly show the pool to any diver who happens to see it, as though it were a pool on land, so in some circumstances very salty water can sink.


How to calculate or find the compressional stress wave velocity, Cp for a rock In Cunningham's paper, "The Kuz-Ram fragmentation model - 20 years on", he makes mention of compressional stress wave velocity, Cp. He only comments that the Cp of granite = 5.2 km/s. I using a relation that includes Cp but the rock type is not granite. A search on Google for the exact mention of compressional stress wave velocity lists only 3 results all of which are either the same paper or refer to Cunningham's paper.

Is there a table where I can check the Cp for the rock type?
Is there a relation that I can use to derive the value of Cp based on other known values of the rock

Any of the above is acceptable. Thanks in advance.

See page 2 here for example: https://pangea.stanford.edu/courses/gp262/Notes/8.SeismicVelocity.pdf .

What you refer to as Cp (as far as I can gather from your linked paper), is in the geophysics world generally referred to as the P-wave velocity (P stands for the primary/pressure/compressional wave; separating it from the S-wave which is the slower secondary/shear/transverse wave mode). It kind of depends on the specific mineralogy, compaction, depth, ... to determine exactly what the velocity is for any given rock. Note that the range of velocities is not particularly great (all values lie within one order of magnitude for typical rocks), so if your method is not particularly dependent on getting the P-wave velocity exactly right, you shouldn't have too much of a problem taking some average value for your rock! If, on the other hand, it is very sensitive to this value, you'll have to make an accurate measurement on your sample (which is not a trivial thing to do at all!).


How do I interpret the specs of a weather balloon? I'm planning a high-altitude weather balloon project (to around 100000 feet, or 30 km) some time down the line to take video and pictures of near space altitudes and I have some questions I need to ask before doing so:

What does the weight of a weather balloon mean such as 150 g, 500 g, 2000 g, etc mean?
What diameter of weather balloon do I need? I'm planning to take upto around 1-2 kg of payload consisting of cameras, Arduino, Raspberry Pi, GPS, parachute etc.

The weight of a balloon determines most of its specifications, though I'm not sure if they are generalized or specific to a manufacturer.  Looking at one supplier we can get a feel for what you need.  For a 1 kg payload it looks like you'd want a minimum of a 1200g balloon.  According to the site linked, this 1200g balloon will have:

6.0 ft diameter at launch
113 ft$^3$ volume at release
320 fpm ascent rate
28 ft diameter at burst
109,000 ft altitude at burst
1190 g free lift

If you need 2kg of payload you'd need to size a bigger balloon.  In general your application is not different from the specs of a normal upper-air sounding launch, so you should be able to spec your balloons directly from suppliers of sounding balloons.  All of the balloons for a 1-2 kg payload should burst above 100,000 feet so it just a matter of picking a supplier and a balloon sized for your payload (per the manufacturer specifications).


Identification of Iguanodon and Maiasaura What are some good ways to distinguish between Iguanodon and Maisaura fossils, or even just pictures of the two dinosaurs?

The easiest way to distinguish iguanodon from maiasaura is to look for iguanodon's hands, which are very peculiar indeed. The hand has five digits. The thumb has a large, prominent spike on it for defensive purposes. The three middle fingers are fused and end in hoof-like nails for walking on all fours. The fifth digit corresponding to our little finger sticks out at an angle from the others and is flexible. It is believed that this enabled it to gather food. It is apparent from these strange forefeet or hands that iguanodon, a herbivore, often stood upright like a biped.


Propagation of sound after lightning In an area of frequent thunderstorms, I notice a 'crack or whoosh' sound if a strike is nearby but little or no thunder. Yet I can hear for 30 seconds or so after a distant flash when the thunder first is heard, the sound starts at a high frequency and then evolves into a deep rumble that can shake the walls. It approaches the sub-sonic. What is the relationship between the distance and the energy of the strike?

Since the sound waves propagate not from a single point source but along the length of the lightning's path, the sound origin's varying distances from the observer can generate a rolling or rumbling effect. Perception of the sonic characteristics is further complicated by factors such as the irregular and possibly branching geometry of the lightning channel, by acoustic echoing from terrain, and by the typically multiple-stroke characteristic of the lightning strike.

In addition, thunder will sound louder when the air near the ground is colder and the air higher in the atmosphere is warmer. This is because the acoustic shock waves get "trapped" in the cold air. Such a temperature difference, called an inversion, tends to happen at night, which is why thunder often sounds louder at night.

See Wikipedia and wisegeek.org


Why is the zonal component of flow in the ocean much larger than the meridional component I am reading an Oceanography Textbook which explains that in the ocean, planetary vorticity tends to be much larger than relative vorticity therefore, the potential vorticity can be simplified to be f/H.

"This requires that the flow in an ocean of constant depth be zonal."

"...in general, currents tend to be east-west rather than north south. Wind makes small changes in relative vorticity, leading to a small meridional component to the flow."

If planetary vorticity is far larger than relative vorticity, how exactly do changes in f (planetary vorticity) cause ocean flow to be more zonal?

It is more of a consistency argument: if a constant-depth ocean with much less relative vorticity than planetary vorticity is to stay that way, the flow must be zonal.

If there were significant meridional velocities, they would cause significant meridional displacements of water masses, which would then, by conservation of angular momentum, no longer have small relative vorticity. (Same angular momentum and same depth means same absolute vorticity.  Different planetary vorticity then means different [in the opposite direction] relative vorticity. If planetary vorticity was zero before the displacement, it isn't anymore afterward.)


Do ocean level rise estimates account for mantle elasticity and plate mass changes? In the mainstream media the problem of ocean level rise is presented rather... over-simplistically - ice melts  -> more water flows into the oceans -> water level rises -> continents sink.

But it is in reality a complex system, it is not like pouring water in a glass... or a lake that resides on a continental plate.

Both continental and oceanic plates float on top of the mantle as both are lighter and lower density, and both exert weight and compress the mantle.

Therefore, if water is removed from continental plates by means of melting ice, the continental plate gets lighter. And when that water migrates to the ocean, the oceanic plate gets heavier. And since for every action there is equal in force and opposite in direction reaction, it seems logical that the now heavier oceanic plate will actually push the now lighter continental plate up, to some extent compensating for or possibly even reversing the change in ocean level relative to the continental plate.

So, do the estimates account for the dynamic properties of that complex system?

Sea level rise estimates use changes in relative mean sea level. The definition being:

  Relative sea level is the sea level related to the level of the continental crust. Relative sea level changes can thus be caused by absolute changes of the sea level and/or by absolute movements of the continental crust.

In general, Mean Sea Level means the 'water level when it is still' (without waves). MSL is averaged over a determined period of time, such as a month or a year and it is measured relative to a fixed mark on the land (benchmark).

As MSL is measured relative to land, it can change due to changes in water volume or due to land movements. That is why we usually refer to it as 'relative sea level'.

Long-term changes of sea level are called "secular" changes and include isostatic changes. The main reason for isostatic changes at a global scale is the Glacial Isostatic Adjustment (GIA).

The body of scientific work related to the contributions by different factors is extensive. For instance, I like Cazenave & Nerem, 2004. Also, there is a lot of information about the relative contributions of each.

 Source: JPL-NASA

There is a lot more information about the regional distribution of sea level rise in: How will sea level rise be distributed across the globe?

Also, here is a good simple explanation of the factors affecting sea level.


Do Pyroelectric gemstones really exist? Can they be found on web market? I just got the curiosity today to know whether the gems that produce electricity non stop without an end exist, and I have found this site.

But I’m having doubts about it, thinking that it could be fake or true, and I need to know what’s you’re opinion regarding this.

Oh and, can the costumer order these types of gems as something for collection? I yes, can you share a link where to drive me to a site where I can order one of these gems?

Yes, pyroelectric gems exist. No, they don't produce electricity all the time. Pyroelectric gems can generate a certain amount of electric potential when cooled or heated.

To cite Wikipedia

  The change in temperature modifies the positions of the atoms slightly within the crystal structure, such that the polarization of the material changes. This polarization change gives rise to a voltage across the crystal. If the temperature stays constant at its new value, the pyroelectric voltage gradually disappears due to leakage current (the leakage can be due to electrons moving through the crystal, ions moving through the air, or current leaking through a voltmeter attached across the crystal)

A full list of all piezoelectric minerals can be found at the website of the Mineralogical Society of America

And yes, you can buy them. Some, like Axinite, were used to remove hair and lint from objects.

There's no site like www.buypiezoelectricgems.com... So you should google them one by one and look for sellers. Or go to a gem fair.


why continents do not subduct In section 1.7 of Geodynamics by D. Turcotte & G. Schubet it is stated that

  "(...) continental crust cannot be destroyed by subduction"

which I cannot completely understand. So far I understand the oceanic lithosphere sinks at the trenches because it cools down and becomes denser (thermal contraction) as it moves away from the ocean ridges. So the logic is: buoyancy will make it descend.

But then again, isn't the continental crust thicker and denser? By the same logic above, it should sink as well.

Am I missing something? Thanks in advance for any comments

It is continental crust which hs the greater buoyancy, so when it meets another plate of continental crust neither can subduct. Instead, they collide, crumple and fold, making them thicker and higher. An example of this is the collision between the Indo-Australian plate and the Eurasian plate, which has formed the Himalayas. Had the Indo-Australian plate been oceanic plate, which is thinner and less buoyant, it would have been subducted.


Is oxygen spread equally on Earth's surface? We know that oxygen comes from trees and plants (photosynthesis), so in the jungle where there are a lot of trees you would expect more oxygen than in the desert where there are no trees. Walking in the desert is tough, but is that also due to there being less oxygen?

I know oxygen averages about 21% of the air.  Diffusion and winds probably means there is at least enough oxygen to live in the deserts and on the poles.  But could the oxygen perhaps be lower in those regions, and what is the minimum percentage that humans need to live?

Vegetative photosynthesis does indeed have a significant effect upon atmospheric oxygen concentrations, as may be seen in the plots of the
Atmospheric Oxygen Research.

The strong seasonal variation in photosynthesis, particularly in high latitude northern hemisphere regions, results in an annual oxygen fluctuation of about 20 ppm (parts per million). Superimposed upon this is the 'dilution effect' of increasing carbon dioxide, mainly due to the burning of fossil fuels, such that we are effectively losing about 19 oxygen molecules per million every year. These effects are far less than the short-term fluctuations in available oxygen caused by the weather.
You are correct in saying that the mean oxygen concentration is about 21%. Compare this to the optimal breathing range, for humans, of 19.5 to 23.5% oxygen. People tend to lose consciousness at about 10% oxygen, and die of asphyxiation at about 5% or less.
The above data are for sea-level. At high mountain altitudes the oxygen can be as little as 12%, which is why it is so difficult to climb the highest Himalayan peaks.

Taking the long perspective, even at sea level there has been a a large variation in oxygen content in the atmosphere over the last 550 million years, varying between 10% and 35%.

Don't worry, the human physiology is more than capable of handling normal fluctuations and trends in the atmosphere's oxygen content. But here is  something which you might want to worry about: Suppose international efforts to curb greenhouse gas emissions are negated by continued human population growth? A worst-case scenario can be contemplated in which the global mean temperature rise attains, or even exceeds, 4.5 degrees Celsius during some time next century. In this case, at least a billion people, mainly in the tropics, will be subjected to extreme seasonal heat-stress. At the same time the cumulative effects of oxygen dilution in the atmosphere might become sufficiently high to exacerbate that heat-stress. This is a scenario that does have the potential to kill people.


Which markers could suggest that there was extinct or extant life on Mars? Researchers who are involved in study of life on Mars are saying that there might be multicellular life present on Mars, today or in the past. Which traces, markers or environments on Mars could support this hypothesis and how it will be investigated?

One of the next big missions to Mars, named Mars 2020 is planned to depart from Earth to Mars during late July 2020. This mission involve a very capable rover, like Curiosity on steroids.

From the mission site:

  The mission takes the next step by not only seeking signs of habitable conditions on Mars in the ancient past, but also searching for signs of past microbial life itself.

This mean that there is two important objective:

to find extinct life forms, such as assuming there was conditions a long time ago permitting lifeforms to exist on Mars, likely 3-3.5 Billion years from now or so, in other words, fossils. Why 3-3.5 Gy ago? This was during Hesperian geological epoch when water was likely a major agent in forming channels lakes and rivers, thus with atmospheric and ground conditions possibly permitting the existence of life back then.
to find extant life forms such as bacteria that are existing presently on Mars surface or near surface.

One component of the mission is to sample rocks that are likely lifebearing, analyze and store for a later pickup by a further mission. Lifebearing rocks in that case may be found as old lake beds, for example iron rich lacustrine mudstone.

Lacustrine mudstone is obviously originating from depositing fine sediments over a lake floor, a stable environment through a long time, as shown by layers like this (pictured by Curiosity's MastCam in 2014). And iron rich is important as this chemical arrangement is favoring and helping the preservation of microbial lifeforms.

Source: https://www.nasa.gov/image-feature/jezero-crater-mars-2020s-landing-site

As can be seen in the picture, the big circle (as a crater) in the center of the delta is named the Jezero crater and is the target landing site for Mars 2020. This delta was formed due to water flowing in a lake; clay rich deposited were detected in the area. The crater is exposing deeper (early) layers in the delta, making this an ideal exploration site to look for extinct or extinct life.


Could the 5.7 earthquake in Utah be a precursor to a larger one? Trying to verify the validity of a rumor.

https://earthquake.usgs.gov/earthquakes/eventpage/uu60363602/executive

Short answer: Yes, but the odds are small.

The USGS page that you linked to also links to a forecast: "According to our forecast, over the next 1 Week there is a 1 % chance of one or more aftershocks that are larger than magnitude 5.7."

USGS also notes:

  No one can predict the exact time or place of any earthquake,
  including aftershocks. Our earthquake forecasts give us an
  understanding of the chances of having more earthquakes within a given
  time period in the affected area. We calculate this earthquake
  forecast using a statistical analysis based on past earthquakes.


Is the work "The photochemical origin of life" ,by A.Dauvillier, in line of principle still valid today? Dauvillier, through his studies, demonstrate that a rise of 2 degrees, of the average temperature of the planet represents a point of no return, beyond which an irreversible process would trigger, which would bring the earth to become unfit to originate carbon based forms of life.
My request does not concern the accuracy of the  2°C value, (yet I'm curious of course), but the correctness of the arguments that led Dauvillier to such result.
Is about to know if the path was the right one, while the exact destination my differ.

Would his job, if it were repeated today, in the light of current knowledge, do lead to similar conclusions, or is it based on erroneous assumptions and therefore no longer valid?

Possibly, but they don't apply to today's world

I'm reasonably sure, without having read the book but having looked at summaries online, that Dauvillier was arguing that the conditions on Earth when life first developed were such that life would not have developed if the Earth were 2 C warmer.

First of all, you would need to specify from what baseline the 2 C rise was measured. There are many times in the past where the Earth was at least 2 C warmer than the present and covered in advanced life (possibly up to 10 C warmer at time during the Mesozoic). NOAA suggests that parts of the Neoproterzoic saw global temperatures of 90 F and up, and of course life managed to persist through that.

Since his book is about biogenesis in general, there isn't much comparison to the conditions on Earth today. On that early Earth where life developed, the sun was much weaker (a paradox not completely resolved). There was no oxygen and much more carbon dioxide, ammonia, and/or methane, depending on who you ask. There were also (obviously) no photosythesizing plants and no biological component to the carbon cycle.

Life has profoundly changed how the Earth is. The atmospheric dynamics of the early Earth are not comparable to those of our Earth, and thus a 2 C rise then has almost nothing to do with a 2 C rise now.

Again, I haven't read the book so I can't asses what specific theories Dauvillier made about the early Earth. However, it could be possible that both things are true: a 2 C rise 4.5 billion years ago would have sterilized the Earth forever, and a 2 C rise today would not.


What, exactly, is angle of repose, and where is it in this image? I'm a little mystified by "angle of repose" and the relationship to deposition and transport. In the following image, I detect 2 different angles of repose for the same material. How can this be?

Clearly, the alluvial fan has a very shallow angle to it, not to mention the much steeper alluvial fans to the left. However, an intermittent stream has cut erosional channels through it and exposed a much steeper "angle of repose", which, is likely more reflective of the true angle of repose for this material. So, how is the shallow angle of the alluvial fan possible?

Geological materials such as sediments are never totally homogeneous. There will always be softer and harder regions within sedimentary deposits.

The fact that erosion channels have been created is due to the force/energy of the water creating the channels, the extent of the force the water had when it created the channels, the softness of the material being gouged out and the hardness and cohesion of the material left behind.

The angle of the walls of the channels is not sustainable and over time the walls will slump (fail) to the lower angle of repose you see for the overall deposit. When this occurs the floors of the channels will be filled with the slump material.

In the meantime, when more rain falls, the runoff will naturally flow in the extant channels - the water taking the path of least resistance. The water will flush out the loose slump material and if the force of the water is great enough it may also widened the channel and eventually cause more material to slump into the channel.

A material's angle of repose is a function of its cohesion and it is the overall/average angle the material lies at over a long period of time.


Are El Niños stronger when there is a longer gap from the last El Niño? E.g. see http://www.wired.com/2014/04/el-nino-effects/.

I'm thinking.. In case a major El Niño event didn't happen this year, then would it only make it more likely that a stronger El Niño would happen in a subsequent year?

One issue here is whether El Niño (ENSO) is chaotic in nature. There is a fair amount of literature on the chaotic and deterministic nature of ENSO (e.g., https://www.sciencemag.org/content/264/5155/72.abstract, http://onlinelibrary.wiley.com/doi/10.1029/97GL53639/full). Under the chaotic assumption, the posted question might not have a clear answer.

Then there is the fact that ENSO affects the atmospheric-oceanic energy budget. If too much energy is available, then El Niño might happen, but whether it is stronger is unclear.


Estimate litter production How would one go about estimating litter production (fine root turnover, leaves, etc.) for a forested area? I have some estimates from literature - which were derived from models, but I'd like to create my own estimate to compare.

The 1967 International Biological Programme has a handbook of suggestions for various methods to calculate primary productivity of forests. A subset of these measures would be effective for measuring litter production.

Regarding leaves and other falling litter,

  Bags suspended from hoops (Ovington & Murray 1964) about 1 m above the
  soil. The hoops would be at least 0.5 m in diameter. The bag should be
  freely permeable to water (nylon mesh, cheese cloth, sail cloth, etc.)
  to reduce moisture and decomposition inside the bag. Care must be
  taken with this type of litter trap that the hoop does not incline out
  of the horizontal and the bag must be pegged or weighted to prevent it
  blowing inside out.

Further, the handbook suggests no less than 20 leaf traps in one sample area, and checking contents every week especially in moist areas. Also, to account for branch fall, the weekly collection should check for and weigh fallen branches in a 20m X 20m area.

For fine roots:

  An additional estimate of fine roots can be obtained either by
  excavation of soil monoliths, or by taking soil cores (e.g. Bray,
  Lawrence & Pearson 1959) down to a depth of at least 50 cm and washing
  out the fine roots over a sieve. So far as is possible only live roots
  should be included.

For ground cover:

  Where distinct plants of a single or only a few species are present,
  the best procedure will be to collect a number of individual plants of
  each species (preferably including subterranean organs) at monthly
  intervals through the year. The collected plants are separated into
  leaves, flowers, stems and roots, which are dried and weighed. These
  individual plant data can then be combined with density (number of
  individual plants/area) data for conversion to an area basis. The sum
  of (Species A max. biomass - min. biomass) + (Species B max. biomass min.
  biomass) ... gives an estimate of net production.

I believe that should account for the significant components of litter production.


What does it mean when the depth of earthquakes get near the surface over a period of time? First of all, I am not expert at this so correct me. My hometown is Shiraz and since last year I can sense the earth is moving. I call them  mini earthquakes. But many people around me can not sense it. Some time ago there was an earthquake it felt like a 5 or even 6 richter earthquake but it was a 4 ricther earthquake but then in news they said that the depth was so close to the surface (4 km). I take a look at the USGS archives for Shiraz with in a 90 km diameter (as back in time as it was available) which I think will cover the major and minor fault lines. If you want to take a look its at a link! usgs archives[a]
. And here is a diagram I made in excel.

This is depth diagram (horizontal axis is the time and starts from 1974). What is interesting for me is that the depth of the earthquakes broke the boundary of 10km and stayed there for a much longer than it used to.And here is the magnitude diagram

This is the map of major fault lines of Iran:

This is the same map (only the reverse fault lines):

And again the same map (only the lateral fault lines):

Is this a sign of fault lines building pressure? And why the depth of earthquakes are getting near the surface? Can a geologist make any kind of guess based on the pattern or this is not a pattern at all?

The data from USGS is somewhat misleading.

Determining earthquake depths is a difficult problem, particularly if you're using data recorded a long way from the earthquake. Event location methods often become unstable for very shallow earthquakes. With some methods/catalogues it is therefore normal to "fix" the depth of shallow earthquakes, and not attempt to find a more accurate depth. This is why you see so many earthquakes supposedly at 33km; I think the 10km ones may also be fixed. Really, this ought to be made more obvious in the USGS site (I think the information is there if you dig deep enough!).

So, it's impossible to draw any conclusions from these graphs: you're probably just seeing improvements in seismological techniques over time.


Where can I find a table of ocean temperature pressure and depth What type of data is available for ocean depth and density?  For instance, are there measurements of density near Greenland or Antarctica that could be compared to the central Pacific?  It would be nice to have temperature and salinity measurements to go along with the density values.  Also, how deep and how often are measurements made of density as a function of depth in the ocean?

There are several global products for temperature, salinity and pressure. The product that has been evolving for the longest is likely the World Ocean Database and World Ocean Atlas Series (https://www.nodc.noaa.gov/OC5/indprod.html) and their latest product WOA13 is very high quality (https://www.nodc.noaa.gov/OC5/woa13/). They also have the entire database of used observations.

A way to get a global database and also a way to visualize it and extract information is HydroBase.

Another fabulous product that includes global information available monthly for the period 1900 to the present is provided by the Met Office Haddley Centre. Their latest product is excellent.

If you are looking for model results, one option is to look at the global operational solutions as part of the GODAE initiative. A list of products is here. Their model products include data assimilation, which helps the model from going to far from reality. The one I am most familiar with is HYCOM, which provides global data assimilative products at 1/12 degree resolution.


Live video feeds for submarine ROVs? I know of two live video channels showing live feeds of rover dives:

Okeanos Explorer for dives with the NOAA Ship Okeanos Explorer.

Nautilus live for dives from the Nautilus, operated by the Ocean Exploration Trust.

Does anyone know others?

SOI operates Falkor, which also broadcasts live video. They stream via youtube, currently, as does OET.

https://schmidtocean.org/technology/live-from-rv-falkor/

Occasionally other operations, such as Woods Hole, will operate telepresence cruises, but these three are consistent operators in the space as they have dedicated ROVs and satellite equipment/contracts for their ships. They co-publish an annual supplement to The Oceanography Society's spring issue:  https://tos.org/oceanography/issue/volume-32-issue-01-supplement

-Ethan (formerly with OET)


Where on Earth is the highest none polar magnetic fields? Is there anywhere that magnetic ore deposits are strong enough to have a magnetic field that would be stronger then
Earths' magnetic poles by proximity?

I'm not asking Where on Earth is the magnetic field intensity stronger? In other words where might be a natural place on Earth that would over power a compass and then some? Is there a map of those magnetic field lines minus the Earths' polar magnetic field lines?

In other words where might be a natural place on Earth that would over power a compass and then some

Just about anywhere where the rocks are rich in iron. This would occur near iron ore, basalt, gabbro, and similar iron-rich rocks. You really don't need a lot of magnetite in the rock for this to move the compass needle. You don't even need magnetite - chromite or pyrrhotite rich rocks may be enough to move the compass needle off.

This is a common problem when navigating only using a compass in basalt rich areas. A good historical example is that of Tasmania. You can read about it the following article:

Magnetic rocks—their effect on compass use and navigation in Tasmania

As for a map, you're probably looking for a magnetic anomaly map.

Here's an attempt to make a global , or this one from USGS, or this one being offered for sale.


What is this Lake Michigan rock? Rock found along northern Lake Michigan, (Charlevoix, MI).  Made up of very thin crystalline layers. There are small, round bubble like bumps that protrude from the surface. Doesn't show well in the picture, but the rock has a sugary appearance.

I can't be definite but my three best guesses are Travertine, Agate and maybe Halite, if it fizzes in mild acid it's Travertine, a form of Limestone, if it dissolves in hot water it's Halite, or Rocksalt, otherwise if it's more or less inert it's probably Agate, an amorphous silicate. I find Halite unlikely, the other two are probably pretty equally likely in that location.


If the earth is a globe, what causes temperature differences across lines of latitude? If the earth is a globe and the sun is 93 million miles away, why is the equator the hottest place on earth?

In terms of distances to the sun, the distance to the equator is almost equal to that as the distance to the poles.

Around January 3, the sun is said to be about 91.4 million miles away, but on July 7, the sun is said to be about 94.5 million miles away. The earth is warmer on July 7 (summer time), and yet it is 3 million miles further than when it is in January, how is this possible?

Polar regions are colder than equatorial ones for a simple reason - geometry.

More specifically, it is caused by the greater angle of the Sun's rays to the surface of the Earth. As you go farther north, the Earth's (mostly) spherical surface bends back from the direction of the Sun's rays, and the same amount of photons are spread over a larger area.

What's more, the closer you get to the poles, this already-attenuated sunlight has to go through more of the Earth's atmosphere, and so more sunlight is scattered, and consequently less will reach the ground.

Here's an image (Thanks, Pont) to show the difference:

Source: Wikimedia Commons. License: CC BY-SA 3.0

The sun's angle is more important to climate differences than the modest variation in Earth's distance to the sun, because the atmosphere is kept warm by the greenhouse effect. It's not the direct light that matters: Air is more or less transparent to the visible light that makes up most of the Sun's spectrum. Instead, the ground absorbs that light and reradiates it as infrared and microwave radiation. That longer-wavelength radiation is absorbed by the atmosphere, but if the ground is not radiating as much infrared because it absorbed less sunlight, the atmosphere above it doesn't get warmed quite so much.

Granted, if the Earth's orbit were much more eccentric then the variation in distance to the Sun would matter more to climate variation. But it doesn't.

This would happen even if Earth's axis weren't tilted. Polar regions would still be cold and equatorial regions would still be hotter. In fact, the difference would be greater because there'd be less mixing.

The image below shows the what happens to the energy the Earth receives from the Sun:

Source: NASA

That shows an average over the entire Earth. As you approach the poles, the percentage "reflected by clouds and atmosphere" goes up while total energy "absorbed by surface" per unit area goes down. And since ice has a high albedo, this is reinforced by the percentage "reflected by surface".