An international team of researchers led by Ralf Tappert, University of Innsbruck in Austria, reconstructed the composition of Earth's atmosphere of the last 220 million years by analyzing modern and fossil plant resins.
The mineralogist and his colleagues from the University of Alberta in Canada and universities in the US and Spain produced a comprehensive study of the chemical composition of Earth's atmosphere since the Triassic period.
The research team analyzed a total of 538 amber samples from well-known amber deposits worldwide, with the oldest samples being approximately 220 million years old and recovered from the Dolomites in Italy. The team also compared fossil amber with modern resins to test the validity of the data.
The results of this comprehensive study suggest that atmospheric oxygen during most of the past 220 million years was considerably lower than today's 21 percent.

"We suggest numbers between 10 and 15 percent," said Tappert. These oxygen concentrations are not only lower than today but also considerably lower than the majority of previous investigations propose for the same time period.
The researchers also related the low atmospheric oxygen to climatic developments in Earth's history. "We found that particularly low oxygen levels coincided with intervals of elevated global temperatures and high carbon dioxide concentrations," explained Tappert.

Tappert suggests that oxygen may influence carbon dioxide levels and, under certain circumstances, might even accelerate the influx of carbon dioxide into the atmosphere.

According to the results of the study, oxygen may indirectly influence the climate. This in turn may also affect the evolution of life on Earth. A well-known example is of dinosaurs: Many theories about animal gigantism offer high levels of atmospheric oxygen as an explanation.

Tappert now suggests reconsidering these theories: "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."


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