Precambrian Period
(540-4600 million years ago)

The Earth Passes Gas

During the next 1.3 billion years, known as the Archean Eon (28.26 yards long on the "100 Yard Model"),  the  Earth separated itself into layers while it was still liquified.   Denser material settled toward the center of the planet and lighter material rose towards the surface.  This has resulted in the Earth having four major layers, as shown in the diagram on the right.

During this time, the various gases that would make our early atmosphere and oceans were mixed into this molten mess.  These gases now had the opportunity to bubble up and pass through the liquid rock to escape to the surface.  Once the gases passed through, they were kept from floating off into space by Earth's gravity.  Today, our atmosphere  (and to a lesser degree, our oceans) are recycled and renewed through volcanic activity, both on land and under the oceans.  This helps keep our atmosphere from getting 'stale'.

After a time the Earth's exterior began to cool and form a hard crust.  However, due to the roiling convection of the earth's interior, the crust cracked into many pieces known as tectonic plates.  These plates are like giant puzzle pieces of the Earth's crust. The roiling convection also moves the plates around. As tectonic plates collide two things can happen:

1    One plate can slide under the other and dive back into the mantle to melt and be recycled in a future volcanic event, a process known as subduction; or

2    Both plates can be stubborn and refuse to give into each other causing mountain chains to rise along their colliding boundaries.

Separation Anxiety

As two plates move away from each other they open up a gap known as a rift.  This rift allows molten magma to seep up from the mantle to fill in the gap.  The Mid Atlantic Ridge is a well known example of a rift zone

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