From ABC Science, 12 May 2016:
The oldest fossils of cosmic dust ever discovered provide a glimpse into atmospheric conditions above the Earth more than 2.7 billion years ago and could do the same on other planets.
A group of Australian and British researchers uncovered the micrometeorites — which are barely the width of a human hair — from ancient sedimentary rocks in Western Australia’s Pilbara region.
The micrometeorites consist of iron oxide minerals, which suggested they formed when dust particles of meteoritic iron metal were exposed to oxygen as they blazed through the Earth’s upper atmosphere, the researchers proposed in a letter published today in the journal Nature.
This finding challenges previous notions that the upper atmosphere at the time was as low in oxygen as the lower atmosphere, said lead author and geoscientist Dr Andrew Tomkin from Monash University.
“All the previous studies have looked at … the chemistry of the lower atmosphere but nobody had ever actually figured out a way to look at the chemistry of the upper atmosphere before,” Dr Tomkin said.
“Imagine picking a dust grain the width of a human hair out of a 2.7-billion-year-old rock and using that to figure out the chemical structure of the ancient atmosphere.” Read more.