If Earth's history were a calendar year, humans would not appear until the last few minutes before midnight on Dec. 31. During the Proterozoic Eon—2.5 billion years to 543 million years ago—the sun ...
Metamorphic rocks record the transformation of protoliths under varying pressures, temperatures and fluid compositions. Mineral assemblages such as garnet, staurolite and kyanite define metamorphic ...
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