Earth’s History (Part 1): The Precambrian Eon: Hadean Era
The Precambrian Eon began 4.56 billion years ago, with the formation of the Earth. It lasted until 543 million years ago, and thus was approximately 4 billion years long.
It is divided into three eras: Hadean, Archean, and Proterozoic.
Hadean Era (4.56 billion years - 3.8 billion years ago)
The Earth gradually built up more layers, with the heavy elements concentrating in the core, and the lighter ones forming the mantle.
A primitive atmosphere formed, and also oceans. Some life may have formed.
But the Hadean Era was a turbulent, destructive time. Constant meteorite bombardment destroyed the oceans, and melted the rocks. Solar winds and the bombardment blasted away the primitive atmosphere. Any life would have been destroyed.
The Moon
About 4.5 billion years ago - not long into the Hadean Era - a Mars-sized celestial body collided with the Earth, and tore away a large amount of rock.
The rock debris ended up in the atmosphere, held there by Earth’s gravity. Eventually, it cooled and accreted to form the Moon.
The Moon was also bombarded from space, creating many craters. It wasn’t bombarded as much as the Earth, though, as it was smaller and thus had less gravity.
