The future lifespan of Earth’s oxygen-rich atmosphere is approximately billion years, as revealed by a new numerical model of biogeochemistry and climate.
Earth’s surface environments are highly oxygenated, from the atmosphere to the deepest reaches of the oceans, which represents a hallmark of the active photosynthetic biosphere.
However, the fundamental timescale of the oxygen-rich atmosphere on Earth remains uncertain, particularly for the distant future. Solving this question has huge ramifications not only for the future of Earth’s biosphere, but also for the search for life on similar planets to Earth beyond the solar system. A new study published in Nature Geoscience has given answer.
“For many years, the lifespan of the Earth’s biosphere has been debated on the basis of scientific knowledge about the constant brightness of the sun and the global carbonate-silicate geochemical cycle. One of the corollaries of such a theoretical framework is a decrease continuation of atmospheric CO2 levels and global warming on geological time scales. In fact, it is generally thought that the Earth’s biosphere will come to an end in the next few 2,000 million years due to the combination of overheating and shortage of CO2 for photosynthesis. If true, it can be expected that atmospheric O2 levels will also eventually decrease in the distant future. However, it is not clear exactly when and how this will occur, “he says. Kazumi ozaki, an assistant professor at Toho University and lead author of the research.
To examine how Earth’s atmosphere will evolve in the future, Ozaki and Christopher Reinhard, an associate professor at the Georgia Institute of Technology, built a model of the Earth system that simulates climatic and biogeochemical processes. Because modeling the future evolution of the Earth inherently has uncertainties in geological and biological evolutions, a stochastic approach was adopted, allowing researchers to obtain a probabilistic assessment of the lifespan of an oxygenated atmosphere.
Ozaki ran the model over 400,000 times, varying the model parameter, and found that Earth’s oxygen-rich atmosphere will likely persist for another billion years (1.080 +/- 0.140) before rapid deoxygenation makes the atmosphere reminiscent of early Earth, before of the Great Oxidation Event about 2.5 billion years ago.
“The atmosphere after the great deoxygenation is characterized by high methane, low CO2 levels and no ozone layer. The Earth system will likely be a world of anaerobic life forms, “says Ozaki.
Earth’s oxygen-rich atmosphere represents an important sign of life that can be remotely detected. However, this study suggests that Earth’s oxygenated atmosphere would not be a permanent feature, and that the oxygen-rich atmosphere could only be possible during 20-30% of the entire history of the Earth as an inhabited planet.
Oxygen (and the photochemical by-product, ozone) is the most accepted biological signature for the search for life on exoplanets, but if we can generalize this information to Earth-like planets, then scientists should consider additional biological signatures applicable to anoxic and weakly oxygenated worlds in search of life beyond our solar system.