The Earth has witnessed various geological processes, such as tectonic activities, sedimentation, etc, over millions of years. The accumulation of meteorites and compression of materials due to gravitational forces have also occurred. So, I think the density of the Earth must have also increased. Any insights on this? What are some major factors that have contributed to the change in the overall density of Earth?
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$\begingroup$ My guess is, if anything, it has gotten less dense, by an almost undetectably small amount. Meteorite materials are, on average, less dense than the post-Theia Earth. $\endgroup$– SpencerCommented May 30 at 16:05
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$\begingroup$ @spencer the earth is also cooling though $\endgroup$– HarrychinkCommented Jul 23 at 12:06
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No, but, in parts, yes.
The bulk density of the Earth remains unchanged but there have been density changes in parts of it's structure as a result of geological processes:
As material is erupted onto the surface the mantle and in particular the Asthenosphere grows denser as it's chemistry is steadily stripped of lower density rock forming elements (in particular Carbon and the light Alkali and Alkaline Earth metals. As more lighter rock material is ejected from the mantle the Crust lowers in average density while also increasing in total mass and volume. These are geologic processes and slow ones even on that timescale now, most of the differentiation happened as the crust formed at the end of the Hadean. So it's not something that's particulars visible over even millions of years but when you compare ophiolites of vastly different ages you do see changes in chemistry and density over billions of years.
A similar process is thought to be under way at great depths within the planet's core as well. Earth is still slowly cooling and, it is thought, as it does so the solid Inner Core slowly (~1mm in diameter per year) grows through deposition of Nickel-Iron from the liquid Outer Core. This removes Iron and Nickel (and probably other heavy elements) from the molten outer core and slowly decreases it's density as it's chemistry is relatively enriched in lighter elements.
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$\begingroup$ Thank you for providing the insights! $\endgroup$ Commented May 31 at 6:48