© Lloyd, Charles Chandler

 

Forming Earth

It appears that the Earth formed (accreted) through a series of collisions with other growing objects (planetesimals) in the solar disk, a number of which had iron cores. Each collision added iron to the core and produced a "magma ocean" whose size depended on the size of the impactor and the size of the growing Earth. With each impact, water and heat-producing elements rose towards the surface. Eventually they became concentrated there. This left the Earth with a depleted mantle and an iron core. Modelling indicates that Earth accretion and core differentiation occurred simultaneously from roughly 20 major impacts over about 30 million years10.