Venus would have had oceans long after life began on Earth


Venus was photographed by the Magellan spacecraft. Credit: NASA/JPL

Today Venus has a dry, oxygen-poor atmosphere. But recent studies have suggested that the early planet may have had liquid water and reflective clouds that could maintain habitable conditions. Researchers at the University of Chicago, Department of Geophysical Sciences, have built a new time-based model of the composition of Venus’s atmosphere to explore these claims. Their findings have been published in Proceedings of the National Academy of Sciences.

Water is ubiquitous in our solar system, usually in the form of ice or atmospheric gasalthough sometimes in liquid form. on both planetsmany moons, from the outer ring of the inner asteroid belt to the icy Kuiper belt, and the exit to the second distant Oort cloud light years Far, the water is there.

Venus is hot, dry, rocky planetis slightly smaller than ours, with trace amounts of water vapor in its thick carbon dioxide2 atmosphere, and previous studies attempted to formulate its atmospheric past. Dramatically different weather pictures appear depending on how the previous models were built.

Venus may have always been in a hot, uninhabitable mess, losing oxygen for uptake as the magma ocean crystallized and never formed. liquid water on its surface. Without any means of carbon sequestration, atmospheric carbon dioxide is constantly increasing2 Wrapping the planet in a thick, heavy blanket resulted in current atmospheric pressures at the surface 92 times greater than those on Earth, making Venus hotter than Mercury despite being twice as far away from the Sun. Even a final bombardment by icy comets won’t be enough to keep water on the surface.

Then again, other models point this out early on Solar Systemwhen solar radiation was 30% lower. Venus probably had a moderate surface temperature with a much thinner atmosphere and bodies of liquid water on its surface — perhaps oceans — as late as 700 million years ago, before a runaway greenhouse effect caused it to boil away.

The University of Chicago researchers decided to tackle the issue with their own model. They took the unique approach of first assuming that there was an ocean with a habitable climate, filling in the computer model with many different ocean levels, and advancing those oceans through three different processes of evaporation and oxygen removal. They ran the model with three different time-dependent starting points, a total of 94,080 times, with a scoring system allowing them to select trajectories with results closest to Venus’ current actual atmosphere.

According to the results of the study published in PNASOf the 94,080 tours, only a few hundred were within range of the actual atmosphere of Venus we see today. Hypothetical habitable ages on Venus should end 3 billion years ago with a maximum ocean depth of 300 meters across its entire surface (total hydrosphere). The results indicate that Venus has been uninhabitable for more than 70% of its history, four times longer than some previous estimates.

Scientists are reasonably confident that liquid water on a rocky planet is necessary for life to exist, because we have only one example of life on a wet, rocky planet and nothing else can compare to it. It is believed that life on Earth began about 3.5 to 4 billion years ago, according to Fossil record, going back about 4.5 billion years ago when estimating the molecular clock of evolution. If Venus had liquid water on its surface 3 billion years ago, it could have harbored life as well.

more information:
Alexandra O. Warren et al, A Narrow Range of Early Habitable Venus Scenarios Allowed by Modeling Oxygen Loss and Radioactive Argon Discharge, Proceedings of the National Academy of Sciences (2023). DOI: 10.1073/pnas.2209751120

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