What happens when oxygen drops to zero on Earth?

After the oxygen disappears, a completely different Earth will be born. It is a world filled with methane, low CO2 levels _and no ozone layer.

Life is thriving on our oxygen-rich planet today, but Earth wasn't always like this. Scientists predict that in the future, the atmosphere will return to a state rich in methane and low in oxygen.

Another Earth would be born without oxygen. (Photo: Getty).

While this probably won't happen for another billion years or so, according to a study published in 2021, scientists say that when change does occur, it will be very rapid.

According to predictions, this change would return our planet to a state similar to that before the Great Oxidation Event (GOE) that occurred about 2.4 billion years ago. At that point, humans and most other oxygen-based life forms would reach the 'end of the road,' ending an irreversible cycle.

So scientists hope that humanity will be able to find some way to leave this planet, and go somewhere else in space before it's too late.

"The model predicts that atmospheric oxygen will disappear before widespread loss of surface water and unusual greenhouse conditions in the Earth's climate system," the researchers said.

It is known that the origin of this process comes from changes in the brightness of the Sun , leading to a corresponding decrease in the amount of carbon dioxide as it decomposes.

Less carbon dioxide means less photosynthesis by plants and some organisms, which means less oxygen . 'The drop in oxygen is very, very extreme,' said Chris Reinhard, a scientist at the Georgia Institute of Technology. 'We're talking about about a million times less oxygen than we have today.'

According to Reinhard's calculations , Earth's oxygen enrichment may last only about 20-30% of the planet's lifespan.

What is remarkable is that after oxygen disappears, not all life will end. On the contrary, the life of some species, such as microorganisms, will continue, and they may dominate for a long time before disappearing.

"The post-deoxygenation atmosphere would consist of high methane levels, low _CO2 levels , and no ozone layer at all ," Reinhard said. "Earth would then be a new world of anaerobic life forms ."