The discovery of a new chemical reaction on tiny particulates in the atmosphere could allow scientists to gain a glimpse from ancient rocks of what the atmospheres of the earth and Mars were like hundreds of millions years ago, scientists said.

A team of chemists at the (University of California) UC San Diego said the findings also provided a simple chemical explanation for the unusual carbonate inclusions found in a meteorite from Mars that was once thought by some scientists to be evidence of ancient Martian life.

Team leader Mark Thiemens, dean of the university’s division of Physical Sciences, whose study is detailed in the American journal Proceedings of the National Academy of Sciences, said: “We never knew before how the atmosphere could be trapped in carbonate.

“This chemical reaction, which takes place on the surface of aerosols in the atmosphere, not only provides us with an understanding of how these carbonates can form on the earth and Mars.

“It gives us a new tool to better understand climate change, as our planet warms and becomes more dusty.”

The chemical reaction was discovered by Robina Shaheen, a postdoctoral researcher. She detailed its importance in the Earth’s atmosphere after four years of experiments in which she found a higher than expected proportion of oxygen 17 isotopes in the carbonates found on dust grains, aerosols and dirt from various parts of the world.

Martian meteorites, such as ALH84001, have carbonates with similarly high oxygen 17 anomalies.

Scientists have long attributed the anomalies to photochemical processes involving ozone and carbon dioxide in the thin atmosphere on Mars, which is bathed by intense ultraviolet radiation.

After finding similar anomalies on terrestrial carbonates formed in atmospheric aerosols, Dr Shaheen deduced they might be the result of another chemical process more common to both planets.

She analysed both in the laboratory and in the Earth’s atmosphere how ozone molecules interacted with oxygen-bearing mineral aerosols from dust, sea spray and other sources to form hydrogen peroxide and carbonates containing this same oxygen-isotope anomaly.

Dr Shaheen said Nasa’s Phoenix lander recently detected carbonates associated with particulates in the dusty atmosphere of Mars.

Dr Thiemens said: “What she found is that the tiny little layer on the outside of the grain is where this chemistry all happens. It’s the ozone in the atmosphere mixing with water and carbon dioxide that drives a completely different kind of chemistry, one that’s not in any of the models.”

The new discovery also offers the possibility of mining information about the Earth’s atmosphere, particularly its oxygen levels, from carbonates found in ancient rocks millions of years ago, far beyond the time period from which scientists can now obtain details about the ancient atmosphere from ice cores.

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