4 ms·
I'm not sure if I understand entirely what you're asking, but I think it comes down to "planetary differentiation". It's the same process by which water floats
by AlanSE 13y ago
I'm not sure if I understand entirely what you're asking, but I think it comes down to "planetary differentiation". It's the same process by which water floats on top of oil because of density. The heavy stuff floats to the bottom and the light stuff floats to the top. That process isn't 100% complete obviously, but that's because near the surface material strength matters a great deal. We still have mountains on Earth, which are clearly not behaving like a liquid. If it was behaving like a liquid, then you're right that the heavier parts would upturn the lighter parts and sink. But Earth still has density variations because the process isn't complete, and tectonic movement keeps rearranging it all.
- dredmorbius 13y agoFriction and timescales also matter. The Earth is highly plastic ... on geological timescales. The continents move, the Himalaya are rising at the rate of about 5 mm per year, and one theory of the post-Messinian flooding of the Mediterranean basin (https://en.wikipedia.org/wiki/Post-Messinian_flood_of_the_Mediterranean https://en.wikipedia.org/wiki/Post-Messinian_flood_of_the_Me...) is that a fragment of one of the colliding plates in the region broke off and sank into the lithosphere. The whole system is dynamic, and driven by both latent gravitational heat of formation and by radioactive decay (including postulated naturally occurring fission reactors within the outer core / inner mantel: http://www.nature.com/news/2008/080515/full/news.2008.822.html http://www.nature.com/news/2008/080515/full/news.2008.822.ht... -- a fission reactor near the surface was found in Gabon, within Africa, active about 1.7 billion years ago: https://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor https://en.wikipedia.org/wiki/Natural_nuclear_fission_reacto...). But it's an interesting rock we crawl about.