The Precambrian eon is vast ... Prelude to life (4,550-3,900 mya) Planet Earth is very hot at its formation. As it cools and its mass increases, its gravitational field strengthens.

Precambrian time covers the vast bulk of ... remains of plants and animals buried when the sediments were formed. The Earth was already more than 600 million years old when life began.

A lot has happened in that time. Earth formed and oxygen levels rose in the foundational years of the Precambrian. The productive Paleozoic era gave rise to hard-shelled organisms, vertebrates ...