Amber Reveals What Earth's Atmosphere Was Like 220 Million Years Ago

Earth's atmosphere isn't the same now as it was millions of years ago. Actually understanding what gases composed this ancient atmosphere, though, has long been a challenge. Now, scientists have used gases trapped in amber to reconstruct the atmosphere of the last 220 million years of Earth's history.

The recent findings weren't easy to come by. There's a lack of useable sample material, and collecting enough amber to reconstruct the Earth's atmosphere was a difficult process. Yet amber does have the advantage that it remains chemically and isotopically almost unchanged over long periods of time.

The scientists analyzed 538 amber samples from well-known amber deposits wordwide. The oldest samples were around 220 million years old and were compmared against modern resins in order to test the validity of the data.

So what did they find in the end? It turns out that atmospheric oxygen during most of the past 220 million years was considerably lower than today's 21 percent. In fact, it was likely around 10 to 15 percent. These concentrations are significantly lower than previous estimates proposed.

"We found that particularly low oxygen levels coincided with intervals of elevated global temperatures and high carbon dioxide concentrations," said Ralf Tappert, one of the researchers, in a news release. "Basically, we are dealing here with simple oxidation reactions that are amplified particularly during intervals of high temperatures such as during the Cretaceous period."

In the past, it's likely that an increase in carbon dioxide levels caused by extremely strong volcanism was accompanied by a decrease of atmospheric oxygen. The comparatively low levels in the recent past, in contrast, could be attributed to the absence of large scale volcanism events and an increase in atmospheric oxygen. This, in turn, seems to show that oxygen may indirectly influence climate.

That's not all, though. If the oxygen concentrations indirectly influence climate, then they may also affect the evolution of life on Earth.

"We do not want to negate the influence of oxygen for the evolution of life in general with our study, but the gigantism of dinosaurs cannot be explained by those theories," said Tappert in a news release.

The findings reveal a little bit more about our ancient Earth's atmosphere. This, in turn, gives scientists further insight into the evolution of animals and how our planet and climate has changed over time.

The findings are published in the journal Geochimica et Cosmochimica Acta.