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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.
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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.
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