One billion years from now, Earth’s atmosphere will contain very little oxygen, making it uninhabitable for complex aerobic life.
Today, oxygen makes up around 21% of Earth’s atmosphere. Its oxygen-rich nature is ideal for large and complex organisms, like humans, that require the gas to survive. But early in Earth’s history, oxygen levels were much lower – and they are likely to be low again in the distant future.
Kazumi Ozaki at Toho University in Funabashi, Japan, and Chris Reinhard at the Georgia Institute of Technology in Atlanta modelled Earth’s climatic, biological and geological systems to predict how atmospheric conditions on Earth will change.
The researchers say that Earth’s atmosphere will maintain high levels of oxygen for the next billion years before dramatically returning to low levels reminiscent of those that existed prior to what is known as the Great Oxidation Event of about 2.4 billion years ago.
"We find that the Earth’s oxygenated atmosphere will not be a permanent feature," New Scientists cited Ozaki as saying.
One central reason for the shift is that, as our sun ages, it will become hotter and release more energy. The researchers calculate that this will lead to a decrease in the amount of carbon dioxide in the atmosphere as CO2 absorbs heat and then breaks down.
Ozaki and Reinhard estimate that in a billion years, carbon dioxide levels will become so low that photosynthesising organisms – including plants – will be unable to survive and produce oxygen. The mass extinction of these photosynthetic organisms will be the primary cause of the huge reduction in oxygen.
Afterwards, life on Earth will be exclusively microbial, says Reinhard. "A world where many of the anaerobic and primitive bacteria are currently hiding in the shadows will, again, take over.”
Terrestrial life will cease to exist, as will aquatic life. The ozone layer – which is made up of oxygen – will deplete, exposing Earth and its oceans to high levels of ultraviolet light and heat from the burning sun.
The research was conducted as part of a NASA project into planet habitability, and the predictions have implications for searching for life on other planets. Oxygen-containing biosignatures are typically used to identify habitable planets.
