Earth's crust was unstable in the Archean eon and dripped down into the mantle

Earth's mantle temperatures during the Archean eon, which commenced some four billion years ago, were significantly higher than they are today. According to recent model calculations, the Archean crust that formed under these conditions was so dense that large portions of it were recycled back into the mantle.

Fuente : http://www.eurekalert.org/pub_releases/2013-12/jgu...