A future without oxygen: Scientists explain what Earth could look like in a billion years - hostile to complex life long way before the Sun dies out

The breathable atmosphere of the earth seems a constant entity, but according to experts it is just a temporary phenomenon of the evolution of our planet.

An analysis conducted through computer simulations shows that within one billion years, Earth can experience the loss of a majority of its atmospheric oxygen. This event is, moreover, like to take place long before the sun attains the late phase of its life cycle and turns into a bigger star.

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This does not necessarily mean that all the living entities on the earth will disappear at once. Rather, the planet will become inhabitable for humans, animals, and other oxygen-dependent organisms, and its atmosphere will revert back to the pre-oxygenated era.

Kazumi Ozaki, from Toho University, and Christopher Reinhard, from the Georgia Institute of Technology, have studied the possible future climate change, atmosphere evolution, and biosphere of the planet through geological timescales.

Their study was published in Nature Geoscience.

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This analysis indicates that oxygen-enriched air may represent only a minor portion of the geological past of our planet, and the planets without oxygen should not be necessarily considered uninhabited.

Earth’s oxygen-rich era is only a chapter in its history

The atmosphere of our planet has not always contained sufficient oxygen to support complex life forms such as humans.

About 2.5 billion years ago, the levels of oxygen increased during the Great Oxidation Event. The scientists think that microorganisms, in particular, oxygen-producing microbes, had a significant impact on this process.

Due to the increasing levels of oxygen in the atmosphere and oceans, the composition of our planet has changed. In result, it has become possible for organisms to evolve and adapt to the production of energy through oxygen consumption.

However, this is not the case forever.

In time, the Sun will become brighter due to its age. As a result, in billions of years, there might be a change in the level of heat on our planet as well as the carbon cycle. It might cause a negative effect on the photosynthesis process used by plants, algae and bacteria to produce energy and generate oxygen.

This paper focuses on the analysis of these related processes that might lead to a transition of Earth to another state.

Computer models point to a rapid loss of oxygen

In order to assess the future fate of the Earth’s atmosphere, the scientists developed a model, which integrates climate dynamics along with biological and geochemical processes.

It included the interaction between the atmosphere, the oceans, the land surface and the living organisms. The increase in the intensity of the Sun and the decrease of the concentration of carbon dioxide in the atmosphere were taken into consideration in the model.

As has been hypothesized before, a crisis of Earth’s biosphere may occur in about 2 billion years due to high temperatures and low carbon dioxide content, making photosynthesis harder and harder.

The current study demonstrates that depletion of oxygen from the Earth’s atmosphere might happen even faster.

More than 400,000 computer simulations were made with different parameters of the model being varied in each of them. In this way, the scientists had the opportunity to analyze various possibilities of the Earth’s future rather than just one scenario.

Under different assumptions, Earth’s oxygen-containing atmosphere will exist for one more billion years, after which a relatively quick process of deoxygenation occurs.

What Earth could look like after oxygen disappears

The atmosphere following the significant reduction in oxygen concentration will be very different from the one that exists at present.

The atmosphere in the proposed model consists of very low oxygen, increased methane and reduced carbon dioxide concentrations. Ozone would no longer exist since ozone requires oxygen-based atmospheric chemistry.

These conditions would make it hard for humans, most other animals and many other living things to exist. With less oxygen available, aerobes would find it hard to exist. Additionally, there would be the issue of the increased ultraviolet radiation due to lack of ozone layer.

Nevertheless, the study proposes that anaerobes, living things that do not require oxygen to live, will still exist. There are some living things that currently exist in areas with no oxygen. They can be found in deep sediment deposits, swamps and even the oceans.

Life on earth after the Great Oxidation Event consisted of organisms that could live in the absence of oxygen. The land masses, water bodies, climate and living things were all different. However, the atmospheric chemistry could favor the existence of organisms that don’t require oxygen.

The findings change how scientists search for alien life

The research has implications beyond Earth.

Astronomers often look for oxygen, ozone, methane and other atmospheric gases when studying exoplanets. These chemicals can act as biosignatures, meaning they may indicate biological activity.

Earth is frequently used as a model for understanding what a life-supporting planet might look like. Since oxygen is strongly associated with plants, animals and complex ecosystems, scientists may be tempted to focus on oxygen-rich worlds when searching for life elsewhere.

But Earth’s own history shows why that approach could be incomplete.

For most of its existence, Earth did not have today’s oxygen-rich atmosphere. Life existed long before oxygen became abundant, and some organisms may continue to survive on Earth after oxygen levels collapse.

A distant planet with little or no oxygen might therefore still contain life. It could host organisms based on chemical processes that do not produce large amounts of oxygen or require it for survival.

The researchers argue that future searches should consider a wider range of atmospheric conditions. Scientists may need to look for biosignatures associated with low-oxygen or oxygen-free environments instead of treating oxygen as a universal requirement.

Earth’s future also places the present in perspective. The oxygen-rich atmosphere that supports modern life is not the planet’s permanent condition. It is one stage in a much longer planetary story—one that began before complex life evolved and may eventually move beyond it.

Frequently asked questions

1. In how long will the Earth exhaust its oxygen?

According to this study, it would be approximately 1 billion years before Earth’s oxygen-rich atmosphere will start losing oxygen at a rapid pace.

2. Would the Sun annihilate Earth first?

This is not the case. Oxygen depletion would happen long before the time comes when the Sun becomes very large in its later stages of life.

3. Will all living things get extinct as the oxygen depletes?

Certainly not. While humans and other creatures would suffer harsh times, some kinds of anaerobic bacteria will still live in favorable habitats.

4. Does a planet need oxygen to sustain life?

Absolutely not. Life thrived on Earth even without oxygen. As per this study, researchers must look for other signs of life on planets where there was not much oxygen in their atmosphere.