How Oxygen on Earth Formed Before Life Began On Our Planet

Scientists are learning a bit more about the early atmosphere of our planet, before life first began. While researchers once believed that there must have been a small amount of oxygen in the atmosphere at first, they weren't sure where this non-life oxygen came from. Now, they may have some answers.

Today, Earth's atmosphere is made up of about a fifteen of oxygen, which is pumped out by green plants as a result of photosynthesis. This oxygen is used by most living creatures on the planet. Yet before the first photosynthetic organism appeared about 2.4 billion years ago, the atmosphere of our planet was mostly made up of carbon dioxide, which is the case on Mars and Venus.

In order to see how oxygen might form in the early atmosphere without photosynthetic organisms, the researchers used a vacuum ultraviolet laser to irradiate CO2 in the laboratory. Vacuum ultraviolet light has a wavelength below 200 nanometers and is typically absorbed by air.

"Our results indicate that O2 can be formed by carbon dioxide dissociation in a one step process," said Zhou Lu, one of the researchers, in a news release. "The same process can be applied in other carbon dioxide dominated atmosphere such as Mars and Venus."

In fact, this one-step oxygen formation could be happening now as carbon dioxide increases in the region of the upper atmosphere, where high energy vacuum ultraviolet light from the sun hits Earth or other planets. This is the first time this reaction has been shown in a laboratory, and could mean that models of the evolution of planetary atmospheres need to incorporate this particular reaction. In addition, the new findings reveal a bit more about our own planet, and could help researchers choose better target exoplanets for study.

The findings are published in the journal Science.