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Fossilised sap points to low oxygen past

Time capsules Amber may not preserve ancient DNA, as in it did in Jurassic Park, but a new study has shown it can provide insights into the air ancient beasts once breathed.

The results suggest dinosaurs inhaled air with far less oxygen than we breathe today and may cause a rethink into how they became so big.

An international team of researchers, led by Ralf Tappert of the University of Innsbruck, recently examined the chemical composition of 538 samples of amber and tree resins dating from recent times to as far back as the Triassic period - 220 million years ago.

Currently, Earth's atmosphere contains approximately 21 per cent oxygen. However, amber samples from the early Cretaceous (100-120 million years ago) suggest the air contained only 10 to 15 per cent oxygen.

The concentration, published in the journal Geochimica et Cosmochimica Acta , is much lower than previous estimates which have been as high as 30 per cent.

Tappert and colleagues calculated the level of oxygen in the atmosphere by comparing the ratio of carbon-12 to carbon-13 trapped in the amber. Higher amounts of carbon-13 indicate lower levels of oxygen.

"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 Tappert.

"Compared to other organic matter, amber has the advantage that it remains chemically and isotopically almost unchanged over long periods of geological time."

Ups and downs

The researchers believe that during the Cretaceous era, volcanic activity may have increased the amount of carbon dioxide in the air, resulting in a warmer environment.

A drop in volcanic activity subsequently saw carbon dioxide levels fall along with global temperatures, leading to the recent Ice Ages and an increase in atmospheric oxygen.

The finding may also cause a rethink about the evolution of gigantism that lead to the time of dinosaurs. It was thought a highly oxygenated atmosphere helped fuel gigantism in insect and animals during the time of the dinosaurs.

"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," says Tappert.

Tappert and colleagues believe it is possible to use this technique to look back even further in time.

"Resin can be used as proxies of atmospheric composition for much of the Cenozoic and Mesozoic, and perhaps even into the Palaeozoic, given that resin-producing plants have existed since at least the Carboniferous (300-350 million years ago)," they write.

"This information will help to more accurately quantify compositional changes of the atmosphere that occurred throughout Earth's history."