Atmosphere locked in time
Amber has long been appreciated for its ability to preserve a moment in time as it encapsulated plant matter, bugs and other organisms. As a tool for ecosystem reconstruction, scientists have learnt a great deal. But recently researchers led by Ralf Tappert of the University of Innsbruck, have begun using amber and other fossil plant resins to reconstruct the composition of Earth's atmosphere from the last 220 million years. The results suggest that atmospheric oxygen was considerably lower in the Earth's geological past than previously assumed.
Often atmospheric conditions are difficult to determine due to the lack of useable sample material. But what Tappert and his team have discerned is that "Compared to other organic matter, amber has the advantage that it remains chemically and isotopically almost unchanged over long periods of geological time."
Tappert, a mineralogist along with colleagues from other universities throughout the world have used amber to produce a comprehensive study of the chemical composition of the Earth's atmosphere since the Triassic period. The interdisciplinary team, consisting of mineralogists, paleontologists and geochemists, use the preserving properties of plant resins, caused by polymerization, for their study. "During photosynthesis plants bind atmospheric carbon, whose isotopic composition is preserved in resins over millions of years, and from this, we can infer atmospheric oxygen concentrations," explains Ralf Tappert. The information about oxygen concentration comes from the isotopic composition of carbon or rather from the ratio between the stable carbon isotopes 12C and 13C.
The research team analyzed a total of 538 amber samples from 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," says 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. For the Cretaceous period (65 - 145 million years ago), for example, up to 30 percent atmospheric oxygen has been suggested previously.
The researchers also relate this low atmospheric oxygen to climatic developments in the Earth's history. "We found that particularly low oxygen levels coincided with intervals of elevated global temperatures and high carbon dioxide concentrations," explains Tappert.
Read more at the University of Innsbruck.
Amber image via Shutterstock.