Dropping oxygen levels will eventually lead Earth to a widespread suffocation event

Earth was not always an oxygen-rich world. Researchers believe that the atmosphere will return to a methane-rich, low-oxygen state in the future.

This is unlikely to occur within any of our lifetimes. In fact, it is unlikely for at least a billion years or so. But according to research published in Nature Geoscience earlier this year, the change will be rapid when it happens. This shift will return Earth to a state similar to that which existed before the 2.4-billion-year-old Great Oxidation Event (GOE).

Increased solar radiation will eliminate aquatic environments from the surface of our planet in around 2 billion years. Researchers used comprehensive models of Earth's biosphere to get at their discoveries, taking into account fluctuations in the Sun's brightness. Less carbon dioxide causes fewer photosynthesizing creatures like plants, which means fewer oxygen-producing species.

Furthermore, the scientists behind the present study state that atmospheric oxygen is expected to be a persistent feature of Earth-like planets in general. This has consequences for human attempts to find evidence of life further out in the universe.

Researchers believe that in order to have the highest chance of finding life, we may need to look for other bio-signatures besides oxygen. Their research is part of NASA's NExSS (Nexus for Exoplanet System Science) initiative, which looks into the livability of planets other than Earth. According to their estimations, Earth may only live for 20-30% of the planet's total lifespan, with microbial life continuing long after humans and other larger species have vanished.