The sediment layer would have to be less than a km (half a mile) thick in order to have the observed effect, and would probably cover only patches of the outer core.

BBC: Earth's wobbles reveal deep secrets

To preserve them for more than a billion years to make fossils out of ephemera a site first has to coat its remains in a fixative: a thin layer of waterproof sediment that will slowly harden into stone.

NEWYORKER: The Martian Chroniclers

In the deep water, large swaths of Wilcox sediment slumped over the side of the continental shelf and were swallowed by a layer of salt that dates back to when the American continents pulled away from Europe and Africa.

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