New answers tagged

12

The answers above do a fine job already. But I'll try to add a simple thought experiment. Imagine three objects floating in space, clumping together by gravity: ### ### #A#|c|#B# ### ### Mass A, the negligible mass c and mass B, equal to A. The center is attracted to A and B and their gravity cancels out. However, A presses against c, because it is ...


9

Pressure at the center of the earth is non-zero. You're correct that there's no gravitational force at the center of the earth, but that doesn't mean pressure is zero - the pressure comes from the many miles of rock sitting above the center of the earth. As an analogy, think of a balloon. The pressure inside is higher than ambient because the elastic skin of ...


3

Imagine the whole ball being separated into a handful of concentric shells, with the outermost shell being the crust with the surface, and the lower shells ever more deeper, hotter, and ghastly regions of the internals of our planet. Now, just for the thought experiment, forget that each individual shell has "stuff" going on in itself, and just ...


31

It is the pressure gradient that is proportional to the local gravitational force. When that force is integrated over a distance, the pressure gradient is integrated to accumulate a total pressure. The maximum occurs at the point towards which gravity is directed in a spherical mass, which is the center. True, gravity at that point is zero, but it and ...


-1

it looks like a gastropod, as there are no septa. Maybe it is Malayaspira, which is Ordovician


2

What you are asking about is the formation of sandstone. There is more to the process than just applying pressure; chemical changes, pressure, water and heat are all involved in the process. When sand deposits accumulate they undergo a process called diagenesis, which involves, physical and chemical changes in sediments first caused by water-rock ...


0

I want to contribute to the excellent answers already given pointing out two things: external color of a rock (altered) can be different from the rock minerals colours the powder of a mineral can be of a different color of the mineral.. for example some metallic color sulphides of zinc have a red powder if scratched.


4

As I understand it, the current explanation for these deposits' existence is the carboniferous period when plants basically evolved woody structures that allowed them to grow trunks and grow tall. This is a minor point, but you're writing about coal rather than petroleum. Most geologists think petroleum is also of biogenic origin, but resulted from sea-...


1

Carbon cycling through the mantle is a hugely important geologic process. Carbon gets into the mantle when subducted continental arc materials bearing rich, organic runoff are carried to depth, then exuded through volcanism at plate boundaries. That rich organic runoff is created by rain which is deeply influenced by... Oceanic currents which largely ...


1

Major geologic changes occur during natural events. Events like wildfire, floods, earthquakes, drought, volcanic eruptions, tsunamis, etc. can severely alter the landscape and allow new geologic processes to take place. For instance, after a landscape is hit by wildfire, it is easily subject to flash flooding and you get soil loss. This was not really &...


4

You could mention the fact that the solid Earth (i.e., not the atmosphere) is slowly cooling down, as the two main sources of heat, primordial and radioactive, are slowly decaying. Because of this, the planet may become tectonically dead at some point. Gradual change over long periods of time is known as uniformitarianism, and has been opposed to ...


15

The effects of Earth's past climate variations on the landscape, especially glaciation, cannot be underestimated. The multiple glacial advances and retreats over the last 4 million years or so have been a major (and sometimes the principal) force that shaped the current landscape. We're actually living in one of the temporary glacial minima - there will be ...


4

By far most naturally occurring hydrates are methane hydrates. However, Dillon[1] documents hydration of other gases including carbon dioxide in some places such as the Gulf of Mexico: Many gas hydrates are stable in the deep ocean conditions, but methane hydrate is by far the dominant type, making up >99% of gas hydrate in the ocean floor. The methane ...


0

If it was produced over hundreds of millions of years, it must be at a very low rate, otherwise we would be up to our armpits in the stuff. Unless it was consumed by bacteria, in which case the atmosphere's oxygen would be used up.


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