The Earth
"It is dawn, 4,600 million years ago. Earth is in the violent red throes of its beginnings..."
-- Margulis & Sagan
In its earliest stage, approximately 4.6 billion years ago, Earth was a fire ball-- a gravitational implosion of molten rocks and swirling metal. Its surface and atmosphere were occupied by gases such as ammonia, hydrogen sulfide, and methane in their superheated states, zapping everywhere and at everymoment by lightning. Meanwhile, the sun has ignited, sending bursts of powerful radiation onto Earth.
Meteors of different sizes, ranging from dust specks to small planetoids, at the same time, continue their bombardments. While these bombardments brought water and carbon compounds along onto Earth, they also brought in incredible amounts of (kinetic) energy, which along with the decay of radioactive isotopes, melted the solid material collected on Earth from the earlier planetesimals(Margulis & Sagan). Gravity then caused abundant, dense iron to sink toward the Earth's center, forcing less dense material to the surface. This process of chemical differentiation then produced a layered structure within the Earth: a central core composed of almost pure iron, surrounded by a mantle of dense, iron-rich minerals. This mantle, in turn, is surrouned by a thin crust of relatively light silicon-rich minerals (Kaufmann).
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