Earth’s atmosphere wasn’t always full of life-giving oxygen — it was once a choking mixture of carbon dioxide and other gases, more like the atmosphere of Mars or Venus.
It’s widely believed that the rise of plants turned that carbon dioxide into oxygen through the chemical reactions of photosynthesis, in a period called the Great Oxygenation Event. But a new study suggests there may be another way to make oxygen from carbon dioxide, using ultraviolet light.
The findings could explain how the Earth’s atmosphere evolved, and hint at a way to make oxygen in space, the researchers said. [7 Theories on the Origin of Life]
Even though scientists think plants produced most of the oxygen present on Earth, they suspected some oxygen may have existed before photosynthetic organisms arose, said Cheuk-Yiu Ng, a physical chemist at the University of California, Davis, and co-author of the study published today (Oct. 2) in the journal Science.
But, it was thought that the planet’s oxygen (O2) formed from two oxygen atoms colliding and combining on some surface, not because the oxygen molecules split from carbon dioxide (CO2), Ng said.
When light breaks apart CO2, the molecule normally splits into carbon monoxide (CO) and an oxygen atom (O). One theory suggested carbon dioxide could potentially be stripped into molecular oxygen (O2) and carbon (C) instead, but “nobody had ever detected” such a process, Ng told Live Science.