Earth’s atmosphere would produce very little oxygen in a billion years, rendering it uninhabitable for complex aerobic existence. Resulting in the extinction of humans unless we start planning for the future.
Oxygen now makes up about 21% of the Earth’s atmosphere.
Its oxygen-rich environment is suitable for large and complex species that need the gas to survive, such as humans.
However, oxygen levels were much lower early in Earth’s history, and they are likely to be low again in the not-too-distant future.
To predict how Earth’s atmospheric conditions will change, Kazumi Ozaki of Toho University in Funabashi, Japan, and Chris Reinhard of Georgia Institute of Technology in Atlanta used models of Earth’s climatic, biological, and geological systems.
According to the researchers, Earth’s atmosphere will retain high levels of oxygen for the next billion years before rapidly declining to levels similar to those that occurred prior to the 2.4 billion-year-old Great Oxidation Event.
“We find that the Earth’s oxygenated atmosphere will not be a permanent feature,” says Ozaki.
One of the main reasons for the change is that our sun will get hotter and emit more energy as it gets older.
As CO2 absorbs heat and then breaks down, the researchers predict that the amount of carbon dioxide in the atmosphere will decrease.
According to Ozaki and Reinhard, carbon dioxide levels will be so poor in a billion years that photosynthesising species, such as plants, will be unable to thrive and produce oxygen.
The main cause of the massive decrease in oxygen would be the mass extinction of these photosynthetic species.
“The drop in oxygen is very, very extreme – we’re talking around a million times less oxygen than there is today,” says Reinhard.
The researchers also predict a simultaneous rise in methane to levels as high as 10,000 times those currently present in the atmosphere.
Once changes in the Earth’s atmosphere start to happen, they will happen quickly: according to the team’s estimates, the atmosphere could lose its oxygen in as little as 10,000 years.
“The biosphere cannot adapt to such a dramatic shift in environmental change,” says Ozaki.
According to Reinhard, life on Earth will be purely microbial after that. “In a world where many anaerobic and primitive bacteria are currently hidden in the shadows, they will once again take control.”
The extinction of both terrestrial and marine life will be inevitable. The ozone layer, which is made up of oxygen, would deplete, exposing the Earth and its oceans to dangerously high levels of ultraviolet light and heat from the sun.
The study was part of a NASA initiative looking at planet habitability, and the findings have implications for the quest for life on other worlds. Biosignatures containing oxygen are often used to classify habitable planets.
“Oxygen is a very significant biosignature because it is so deeply entangled with life on Earth,” says Natalie Allen of Johns Hopkins University in Maryland. However, the latest forecast reveals that the presence of oxygen on a habitable planet is unpredictable and may not be permanent.
According to Kevin Ortiz Ceballos of the University of Puerto Rico, “it means that even for planets around other stars that are very close to Earth, significant quantities of oxygen can not be found in their atmosphere, even though they can sustain, or have supported, complex life.” He claims that the absence of oxygen around planets does not imply that they are uninhabitable.
Other biosignatures, rather than oxygen, may be used to hunt for alien life, according to Ozaki and Reinhard.
Hydrocarbon hazes in a planet’s atmosphere, for example, may provide a more long-lasting indicator of extra-terrestrial existence.