Small objects in the hands of scientists can reveal extremely big facts. Team of researchers, led by the Monash University, now examined the oldest fossil micrometeorites ever found and made interesting discoveries about the chemistry of Earth’s atmosphere 2.7 billion years ago. These finding challenge a long-standing view about Earth’s ancient atmosphere being oxygen-poor.
Analysis of these fossil micrometeorites, known as space dust, revealed that the oxygen levels in the ancient Earth’s upper atmosphere were about equal to ones of today. However, oxygen-rich level of the atmosphere was separated from the oxygen-starved lower atmosphere by a methane haze layer. These are very significant findings and what makes them even more interesting is that they were made by analysing extremely small micrometeorites, extracted from samples of ancient limestone.
Samples of the space dust were collected in the Pilbara region in Western Australia and examined with cutting-edge electron microscopes. Scientists found that most of the samples were particles of metallic iron once, which is common in meteorites. However, these particles have been turned into iron oxide minerals in the upper atmosphere, which means that these layers of Earth‘s atmosphere were oxygen-rich. It is the first time ever scientists managed to sample the chemistry of the ancient Earth’s upper atmosphere.
Calculations showed that oxygen levels in ancient atmosphere were about equal to the ones of today. Dr Matthew Genge, an expert in modern cosmic dust, who performed the calculations, said: “This was a surprise because it has been firmly established that the Earth’s lower atmosphere was very poor in oxygen 2.7 billion years ago; how the upper atmosphere could contain so much oxygen before the appearance of photosynthetic organisms was a real puzzle”. Scientists think that oxygen in the upper layer was the result of CO2 broken down by the ultraviolet light.
It is really interesting to see what scientists can find from studying fossilised particles of space dust the width of a human hair. Researchers already have next steps planned. They will attempt extracting micrometeorites from a series of rocks, trying to learn more about changes in atmospheric chemistry. The great oxidation event, which happened 2.4 billion years ago, will get especially strong attention. We have to wait and see what analysis of such small particles can reveal about the ancient history of our planet.