Amazing stuff!
"... But the atmosphere is an ephemeral thing; direct samples preserved in ice go back only 6 million years—less than 0.2% of the Earth’s history. For all the time before, gauging the air relied on proxies from metals and minerals trapped in ancient rock.
But researchers are now refining ways to directly sample ancient gases trapped as microscopic inclusions in salts, veins of quartz, and crystallized magma. From samples that stretch back more than 3 billion years, they’re extracting direct records of noble gases, oxygen, nitrogen, and carbon dioxide.
Much of this work is still preliminary, but it is already verifying some assumptions about atmospheric history—and upending others.
One group, for example, has recently found direct evidence that oxygen levels were high enough to support animal respiration long before the first animals appeared.
Others are using noble gases extracted from impact craters to track gaps in Earth history, identifying when plate tectonics slowed down. ..."
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