How are scientists able to find out the composition of Earths atmosphere throughout Earths history?

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How are scientists able to find out the composition of Earths atmosphere throughout Earths history?

In: Chemistry

Ice cores in the Antarctic trap the Antarctic atmosphere from the past in tiny pores. They drill out the cores, carbon date the ice, and then very carefully sample the tiny pockets of air. You don’t get much, but from that air you can get a measure of the atmosphere, presuming that then as now the Antarctic atmosphere is mostly the same as the rest of the atmosphere.

In (relatively) recent eras, air can get trapped in ice as it freezes.

When looking at time in fossil records lengths, you can find out from living things; air elements can be found in bones and give indications of composition. This can also be mapped with certain events that affect the biosphere.

Even further back, rocks react to the atmosphere in certain ways. Thus, when you find layers of rock that shouldn’t have formed with high levels of oxygen buried under rocks that would form with higher oxygen counts, it provides an idea of what elements were in the air.