Previous research suggested that carbon dioxide (CO2), encountering sunlight at specific wavelengths, should break down into carbon monoxide (CO), and single atoms of oxygen, which would bind with other atoms to form compounds.

Oxygen in the atmosphere in modern times is produced, by and large, through photosynthesis, carried out by lifeforms. The rise and evolution of photosynthetic life led to the Great Oxidation Event, roughly 2.4 billion years ago. This had an distinct effect on the wavelengths of light striking the surface of the Earth.

Vacuum ultraviolet (VUV) rays, the shortest wavelength of UV light, is absorbed by oxygen high in the atmosphere. However, there was little oxygen in the air until the Great Oxidation Event, allowing these VUV rays to reach the surface of the planet. These frequencies are able split apart molecules of CO2, dividing them into their component oxygen and carbon atoms. This process was theorized to be possible in a paper published in Science Direct in June 2000. Before this new study, it was believed that only small amounts of oxygen were produced on the early Earth, through a more complicated two-step process.

"Our results indicate that O2 can be formed by carbon dioxide dissociation in a one step process. The same process can be applied in other carbon dioxide dominated atmospheres such as Mars and Venus," Zhou Lu, a graduate student at the University of California who led the research, said.

Lu successfully tested this 14-year-old theory in the laboratory, using a mechanism powered by a pair of high-power vacuum ultraviolet lasers. The first laser split the molecules into their component atoms, which then had their electrons stripped off by the second lasers for spectrographic analysis. In the experiment, around five percent of the carbon dioxide molecules exposed to the lasers produced gaseous oxygen. Still, this relatively minor production could have manufactured significant quantities of the gas over millions of years.

This new study could show how molecular oxygen could form in an atmosphere rich in carbon dioxide, without the presence of life to feed the process. Researchers investigating the formation and development of the Earth want to know how the gas may have been produced in the early days of the planet. Astronomers studying how oxygen could be produced in alien atmospheres could also benefit from this research, possibly aiding in the search for alien life.

As carbon dioxide concentrations rise in the upper atmosphere, it is possible that this one-step conversion process could currently producing molecular oxygen high above the surface of the Earth.

Investigation of how carbon dioxide can break down into molecular, gaseous oxygen was detailed in the journal Science.