1.5 Origin and Early Evolution of Earth

A model for the origin of the solar system that supposes a rotating nebula of dust and gases that contracted to form the Sun and planets

The cloud of interstellar gas and/or dust from which the bodies of our solar system formed

• The birth of our solar system began as a cloud of dust and gases started to collapse under its own gravitation • The nebula contracted into a flattened, rotating disk that was heated by the conversion of gravitational energy into thermal energy • The disk’s center formed the Sun. As the rest of the disk cooled, tiny particles of metal, rock and ice condensed with it • Over tens of millions of years, these particles clumped into larger masses, which collided to form asteroid-sized bodies, which accreted to form planets

• As the Sun formed and temperatures declined, materials with high melting/condensing points condensed into particles. • These particles coalesced through repeated collisions into larger bodies called planetesimals. • Over tens of millions of years planetesimals accreted into the four inner rocky planets • Leftover rocky and metallic fragments became meteorites when they impacted Earth • High-velocity impacts and the decay of radioactive elements causes these growing planets to heat up, preventing them from accumulating much lighter elements like hydrogen and helium which remained as gas. 6.The solar wind eventually swept these lighter elements from the inner solar system where they formed the outer planets, gases planets

Mercury, Venus, Earth, and Mars High density material (rock and metals)

Jupiter, Saturn, Uranus and Neptune Low density material (ice and gasses)

Through chemical differentiation, through density with the dense materials (iron and nickel) sank toward the core and lighter materials rose toward the surface