Breathable atmospheres may be more common in the universe than we first thought

Breathable atmospheres may be more common in the universe than we first thought

by Lewis Alcott and Benjamin J. W. Mills, Phys.org

The existence of habitable alien worlds has been a mainstay of popular culture for more than a century. In the 19th century, astronomers believed that Martians might be using canal-based transport links to traverse the red planet. Now, despite living in an age when scientists can study planets light years from our own solar system, most new research continues to diminish the chances of finding other worlds on which humans could live. The biggest stumbling block may be oxygen—human settlers would need a high oxygen atmosphere in which to breathe.

So how were we so lucky to evolve on a planet with plenty of oxygen? The history of Earth’s oceans and atmosphere suggests that the rise to present-day levels of O₂ was pretty difficult. The current consensus is that Earth underwent a three-step rise in atmospheric and oceanic oxygen levels, the first being called the “Great Oxidation Event” at around 2.4 billion years ago. After that came the “Neoproterozoic Oxygenation Event” around 800 million years ago, and then finally the “Paleozoic Oxygenation Event” about 400 million years ago, when oxygen levels on Earth reached their modern peak of 21%.

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