Theory
Formation and differentiation of Earth
Earth, like the Sun and the other planets of our Solar System formed around 4.6 billion years ago from part of a giant molecular
cloud - the cosmic debris of a massive supernova. Out of matter that coalesced in the center of the molecular cloud due to
gravitational collapse emerged the proto-Sun and a surrounding disk of dust and gas. Attraction forces within this rotating
protoplanetary disk that fed the young Sun, led to the accretion of progressively growing objects and planetesimals.
Increasing mass and gravitational forces of the growing planetary bodies resulted in interactions and disturbance in their orbits,
ultimately giving rise to larger collisions.
Earth, as a terrestrial inner planet formed relatively close to the Sun through the
accumulation of rather heavier matter, whereas the outer planets formed from gas that had been blown away in more distal
regions of the solar system (solar wind). Continuous bombardment and larger impacts – including one that led to the
formation of the Moon -, and the radioactive decay within the Earth heated the planet resulting in partial melting.
Different melting temperatures and density contrasts led to gravitational segregation of a heavier iron core and a lighter
silicate mantle. Further chemical differentiation by partial melting of the mantle led to the formation of Earth’s proto-crust.
The Earth’s layering into core, mantle and crust due to this early differentiation remains an essential
feature of the Earth’s structure.