Oxygen on the Earth’s surface was a billion years in the making and will diminish again over the next billion years, researchers say.
(CN) — In a billion years, Earth’s surface will return to a low-oxygen state, according to a new study.
The research published Monday in the journal Nature Geoscience suggests atmospheric oxygen is not permanent, a finding that will likely influence the search for life on other planets. The study was led by Kazumi Ozaki with Japan’s Toho University and Christopher Reinhard of Georgia Tech.
An oxygen-rich atmosphere indicates the possibility of life on a planet and creates a climate for plants and photosynthesis, but the lifespan of this type of atmosphere is uncertain, especially in the distant future.
“It is generally thought that the abundance of O2 in Earth’s atmosphere has been well below that of today for most of Earth’s history, and that the modern atmospheric O2 abundance developed only after the emergence of land plants, which have evolved to accelerate the geochemical cycles of bioessential elements (most importantly phosphorus) in Earth surface environments,” the study states. “Thus, charting the history of planetary oxygenation after the evolution of oxygenic photosynthesis requires an understanding of how biospheric productivity (and the subsequent burial of reduced materials into sediments) changes in response to evolving environmental conditions.” (Parentheses in original.)
Ozaki and his research team found through modeling that atmospheric oxygen levels on Earth will substantially decrease in the long-term future.
This is due to several factors, the researchers found, including increasing temperatures and solar brightening.
The sun brightens and dims intermittently, taking 11 years to complete each solar cycle. Levels of solar radiation rise or fall depending on the sun’s cycle. But other factors – for instance, cloud covering, volcanic activity and oceanic ice – influence how much solar radiation is either absorbed or reflected from Earth’s surface.
An estimated 30% of the sun’s rays currently reaching Earth are reflected back out to space by white surfaces such as polar ice. At the other end of the spectrum, the dark ocean reflects just 6% of the sun’s rays and absorbs 94% of what hits it. According to the researchers’ model, global warming is expected to ramp up as the ice caps continue to melt.
While white surfaces reflect solar rays back out to space, another component of solar activity and how much radiation is absorbed by Earth has to do with organic haze, which is made of particles in the atmosphere that act as a buffer between Earth and the sun’s radiation.
Through long-term modeling, Ozaki’s team concluded that climate stability in the future will be largely dependent upon organic haze, the thickness of which is determined by a ratio of atmospheric methane relative to the amount of carbon dioxide.
“From the perspective of planetary evolution, our results imply that atmospheric oxygenation is not a permanent condition on habitable worlds hosting oxygenic photosynthesis, and that only a fraction of Earth’s history will be characterized by robustly detectable levels of atmospheric O2,” according to the study.
While Monday’s report concludes that oxygen will disappear from Earth’s surface in a billion years, a previous study Ozaki worked on suggested the right conditions for oxygen on the Earth’s surface were a billion years in the making.
Ozaki did not immediately reply to an email request for comment on the latest study.