Earth's hot interior made graveyard of tectonic plates: MIT
An MIT study has found Earth harboured a mantle which was 200 ÂºC hotter 3 billion years ago, while the crust was composed of much denser stuff. The combination of a hotter mantle and denser rocks likely caused tectonic plates to sink to the mantle's bottom, 2,800 km below the surface, forming a "graveyard" of slabs atop the Earth's core.