In a new analysis of cosmic dust obtained from fossilised micrometeorites, researchers have discovered that our idea that Earth’s ancient atmosphere was oxygen-poor was totally wrong.
The cosmic dust was obtained from samples of ancient limestone in the Pilbara region in Western Australia, which have been dated as having fallen to Earth around 2.7bn years ago and, by analysing these microscopic fragments, the research team has thrown atmospheric science a curve ball.
For years, it was generally accepted by the scientific community that around the time these micrometeorites fell to Earth, our atmosphere did not create much of a hospitable life for creatures here on the surface as it was relatively oxygen-poor.
Now, however, a chemical analysis of the samples has shown that they were once particles of metallic iron commonly found in meteorites that had then been rapidly heated into iron oxide minerals in the upper atmosphere.
This discovery revealed that the upper atmosphere of Earth was not oxygen-poor billions of years ago, but rather it had the same amount of oxygen we have today.
A three-layered atmosphere
The reality is that, during this period, the oxygen-rich upper atmosphere layer was then followed by a methane haze layer that separated the upper layer from the oxygen-starved lower atmosphere with little mixing in between.
“A possible explanation for this layered atmosphere might have involved a methane haze layer at middle levels of the atmosphere. 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,” said Dr Andrew Tomkins, who led the study.
“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 make-up of Earth’s upper atmosphere, billions of years ago.”
The team will now look to expand its research by analysing further micrometeorite samples with a particular focus on what is known as the ‘great oxidation event’, which saw a huge jump in the amount of oxygen contained within the lower atmosphere 2.4bn years ago.
Earth’s atmosphere image via Shutterstock