what it used to be and is still evolving over time. You will learn a lot just by studying the different periods, although these are usually broken up further into epochs. Figure 11 shows these in better detail:
Figure 11.
PROTEROZOIC ERA The Proterozoic era is important in geologic time. There was a lot that happened in this era, extending from 2.5 billion to 541 million years back in time. The tectonic plates rested or floated on magma, but the magma then is different than now. The plates were not as thick as they are now, and the magma was both hotter and more liquid. This
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