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ZoneEnder666 t1_iv13qlz wrote

Reply to comment by CrustalTrudger in If the inner core is the hottest part of the Earth, hotter than the liquid outer core, then why is it a solid? by Paradigm7657

The pressure from gravity decreases as we approach the core, right? I always thought the pressure at the core was from confined, radioactive decay, yes? no?

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CrustalTrudger t1_iv1b7kc wrote

Gravitational acceleration decreases with depth as you move from the outer core inward (e.g., this estimate using PREM), but overburden (i.e., the mass above a given point) is still increasing, especially given the large density increase from the mantle to the core, so pressure is definitely still increasing, especially considering the inner core boundary.

EDIT: If you want to directly see estimates of pressure with depth, you can look at table 2 starting on page 312 of the original PREM paper by Dziewonski & Anderson, 1981. Looking at this, you can see that pressure broadly is predicted to increase with depth despite the decline of gravitational acceleration as you approach the center of the planet.

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Coomb t1_iv3iamt wrote

I don't even think it would be possible for pressure to decrease with increasing depth. Pressure must be continuous unless something like a shock exists, and every additional shell adds some amount of gravitational pressure which is greater than or equal to 0. If somehow a situation existed where pressure were higher in outer layers than in inner layers, the pressure would drive movement and compression of the material in between such that the stress developed was adequate to support the pressure.

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mfb- t1_iv3quf8 wrote

A decreasing pressure is physically possible on a small scale (imagine a vacuum chamber placed in the center of an asteroid), but I don't see that happening on a planetary scale.

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Cloudboy9001 t1_iv1b7gh wrote

At a hypothetical exact center of the Earth (assuming, for argument's sake, equal distribution of elements/density in the Earth), a particle of matter would be pulled equally in all directions--balancing out; nevertheless, there is a column of matter on all sides of said particle pushing down on it.

From what I gather, it's believed that there is significant but not extremely substantial heat generated from ongoing rasioactive decay. (It's thought that billion uranium deposits may have naturally undergone criticality/self-susutaining fission.)

The state of matter is a function of both temperature and pressure. Propane at modest pressure can be stored as a liquid that turns into a gas at atmospheric pressure during use. Water in a pressure cooker (about 2x atmospheric pressure) has a boiling point of around 120 degrees C; conversely, food cooked on a tall mountain may take much longer due to a less massive column of air pressing upon the water (which lowers its boiling point).

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CrustalTrudger t1_iv1biv8 wrote

> From what I gather, it's believed that there is significant but not extremely substantial heat generated from ongoing rasioactive decay.

This depends on where you are. I.e., this is broadly correct for the core specifically in that we don't consider there to be many radioactive elements in the core. However, in terms of the total internal heat budget, radioactive heat production accounts for roughly half of the heat budget, but this is primarily from elements in the mantle and crust.

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