What gases were in the early earth's atmosphere?

Surprisingly thin earth atmosphere

The earth's atmosphere extends to an altitude of around ninety kilometers. All gases from nitrogen to oxygen to carbon dioxide add up to a mass of around five quadrillion tons. The earth's atmosphere was significantly lighter just under three billion years ago. This is the conclusion reached by geoscientists who have analyzed fossil gas inclusions in lava rock. As they report in the journal "Nature Geoscience", this discovery contradicts the previous assumption that the atmosphere in this early epoch of earth's history could have been denser than it is today.

"These rocks are like a history book for the earth, as they store the environmental conditions at the time they solidify," says Sanjoy Som of the Blue Marble Space Institute of Science in Seattle. With the help of X-rays, the researcher and his colleagues examined samples of solidified lava flows that solidified 2.7 billion years ago in what is now Australia in the so-called Pilbara craton. The volcanic rock contained gas inclusions that filled with minerals over the course of millions of years. However, the structure of the bubbles was retained and today it can provide clues about the atmosphere at that time.

During this earth epoch, oxygen did not yet exist in the atmosphere, which must have been rich in nitrogen above all. The current measurements showed an air pressure of around 230 millibars, which was much less pronounced than it is today. Som and colleagues were able to set the upper limit for the maximum air pressure at around 500 millibars. Their measurements thus contradict other theories that assume a significantly higher air pressure than today.

2.7 billion ago there was already liquid water on earth with a high degree of certainty, but due to the low air pressure it would have evaporated at almost sixty degrees Celsius. But why it was warm enough for liquid water in the first place is a mystery. Current theories assume a strong greenhouse effect caused by large proportions of greenhouse gases such as methane or carbon dioxide in addition to nitrogen in the thin earth's atmosphere.

These results are not only interesting for research into the history of the earth. They also play a role in assessing exoplanents and the chances of life. "The early Earth cannot be compared with the Earth today, but rather with an exoplanet," says Som. Because there was no oxygen and only single-cell organisms could exist. In addition, the planet rotated much faster than today, the solar radiation was weaker and the moon was closer to it. The result was shorter days and higher tides than today.