These micrometeorites consist of iron oxide minerals that formed when dust particles of meteoritic iro

Andrew Tomkins

The oldest space dust yet found on Earth suggests that the ancient atmosphere of Earth had significantly more oxygen than previously thought, a new study finds.

Although oxygen gas currently makes up about one-fifth of Earth's air, there was at least 100,000 times less oxygen in the primordial atmosphere, researchers say.

Previous research suggests that significant levels of oxygen gas started permanently building up in the atmosphere with the Great Oxidation Event, which occurred about 2.4 billion years ago.

This event was most likely caused by cyanobacteria — microbes that, like plants, photosynthesize and release oxygen.

"The project started out as a student research project, and it was a bit of a risk to try and find micrometeorites when few other people had tried it before.

They are cosmic spherules — remnants of meteorites the size of sand grains that broke apart during atmospheric entry.

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