What percentage of 4 billion year old rocks are still on earth? What percentage of rocks currently on the earth bear traces of humanity?
When I've gone on Geology 101 field trips, once or twice the instructor was like "And this rock was formed over a billion years ago." It was invariably followed by "Deep within the earth's crust, several miles below the surface." Rocks that are on the surface get weathered and eroded; quartz and feldspar on exposed granite become successive layers of sandstone.
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What percentage of 4 billion year old rocks are still on earth? What percentage of rocks currently on the earth bear traces of humanity?
When I've gone on Geology 101 field trips, once or twice the instructor was like "And this rock was formed over a billion years ago." It was invariably followed by "Deep within the earth's crust, several miles below the surface." Rocks that are on the surface get weathered and eroded; quartz and feldspar on exposed granite become successive layers of sandstone.