Why Evolution Took a Billion Year Break

About 2 billion years ago, life mastered photosynthesis.  This was an incredibly important evolutionary step, as air filled with oxygen is of course a prerequisite for life as we know it.  However, after photosynthesis had been mastered, evolution took a break.  A long break.  More than a billion year break, as it wasn't until about 750 million years ago that things began evolving again.  Scientists think that they may have a reason for this pause, the entire planet, geologically speaking, was also on break.

Plate subduction could only occur once the mantle had cooled.

We've known for a while that Earth's active plate tectonics was an important factor in the development of life, but for a long time, the Earth's plates weren't doing very much.  The continents grew quickly early in the Earth's life, but about 2 billion years ago, the process stopped, because the mantle was still too hot for plate tectonics as we know it to commence.  Plates couldn't slide into the mantle at subduction zones.  So for a billion years the plates sat around, waiting for the mantle to cool off.  This finally happened about 750 million years ago, when the Earth once again became geologically active.  The supercontinents that had dominated the Earth for a billion years broke apart, and new ecosystems were created, allowing for the evolution of life once again.

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