Scientists believed that the early Earth’s atmosphere contained poor concentration of oxygen. However, a study published online on May 11 in the journal Nature reveals that the oldest fossil micrometeorites or space dust contain proof that Earth’s ancient atmosphere 2.7 billion years ago had the same amount of oxygen as today.

“Using cutting-edge microscopes we found that most of the micrometeorites had once been particles of metallic iron – common in meteorites – that had been turned into iron oxide minerals in the upper atmosphere, indicating higher concentrations of oxygen than expected,” says lead researcher Andrew Tomkins. “This was an exciting result because it is the first time anyone has found a way to sample the chemistry of the ancient Earth’s upper atmosphere.”

The researchers from the Monash University, Australian Synchrotron, and Imperial College, London explain that a methane haze layer present at the time separated the lower atmosphere, which had poor oxygen from the upper atmosphere, contained high levels of oxygen stemming from the breakdown of carbon dioxide by ultraviolet light.

ancient atmosphere

This is one of 60 micrometeorites extracted from 2.7 billion-year-old limestone, from the Pilbara region in Western Australia. Credit: Andrew Tomkins

“A possible explanation for this layered atmosphere might have involved a methane haze layer at middle levels of the atmosphere,” Tomkins adds. “The methane in such a layer would absorb UV light, releasing heat and creating a warm zone in the atmosphere that would inhibit vertical mixing.”

Tomkins says their next research will provide more details about young Earth’s atmospheric conditions. Moreover, they will concentrate on an event known as the great oxidation event, also known as oxygen catastrophe or oxygen crisis.

“The next stage of our research will be to extract micrometeorites from a series of rocks covering over a billion years of Earth’s history in order to learn more about changes in atmospheric chemistry and structure across geological time,” concludes Tomkins. “We will focus particularly on the great oxidation event, which happened 2.4 billion years ago when there was a sudden jump in oxygen concentration in the lower atmosphere.”