Gravitational accretion on the Earth culminated in the differentiation of the planet: the creation of the core
(the source of the Earth's magnetic field) and the beginning of the
atmosphere. About 4.4 billion years ago, the core - which, with the
mantle, drives the geothermal cycle, including volcanism - formed. Gases
emerging from the interior of the planet formed the atmosphere. The
surface of the Earth cooled to form a crust.
The Earth's surface is made up of gigantic rocky "plates" of crustal
material, called the lithosphere, which consist of the rocky outer
coating of the Earth (the crust) and the upper part of the less solid
material (the mantle) that is found below the crust. The plates are moving
very slowly, riding on top of more fluid layers beneath - colliding and
separating.
Gravitational accretion on the Earth culminated in the 
