The case of the cosmic clues
Periodically, the universe sends humans subtle hints about its origins. Well, they’re subtle in the sense that they’re hard to decode. They’re less subtle in the form they take – rocks that hurtle to Earth from the sky. It was hints like these that helped a Monash University-led team discover that the Earth’s upper atmosphere contained as much oxygen 2.7 billion years ago as it does today. This is remarkable for three reasons. First, the accepted theory was that the upper atmosphere at that time was chemically similar to the lower atmosphere – that is, starved of oxygen. Second, until now, scientists had no way to test that theory. And third, the discovery was made not by looking heavenwards, but by digging deep into the ancient limestone of the Pilbara region in Western Australia.
It was from there that Dr Andrew Tomkins and a team from the School of Earth, Atmosphere and Environment at Monash extracted the oldest fossil micrometeorites – or space dust – ever found on Earth.
Dr Tomkins and his team then worked with the Monash Centre for Electron Microscopy and the Australian Synchrotron to examine the samples. And researcher Dr Matthew Genge, an expert in modern cosmic dust at Imperial College London, performed calculations that showed oxygen concentrations in the upper atmosphere were close to modern-day levels. These remarkable results were recently published in Nature.
“It is incredible to think that by studying fossilised particles of space dust the width of a human hair, we can gain new insights into the chemical makeup of Earth’s upper atmosphere, billions of years ago,” Dr Tomkins said.