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Finding potentially habitable planets beyond our Solar System is no easy task. While the number of confirmed extra-solar planets has grown by leaps and bounds in recent decades (3791 and counting!), the vast majority have been detected using indirect methods. This means that characterizing the atmospheres and surface conditions of these planets has been a matter of estimates and educated guesses.
Similarly, scientists look for conditions that are similar to what exists here on Earth, since Earth is the only planet we know of that supports life. But as many scientists have indicated, Earth’s conditions has changed dramatically over time. And in a recent study, a pair of researchers argue that a simpler form of photosynthetic life forms may predate those that relies on chlorophyll – which could have drastic implications in the hunt for habitable exoplanets.
State - Study - International - Journal - Astronomy
As they state in their study, which recently appeared in the International Journal of Astronomy, while the origins of life are still not fully understood, it is generally agreed that life arose between 3.7 and 4.1 billion years ago (during the late Hadean or early Archean Eon). At this time, the atmosphere was radically different from the one we know and depend upon today.
Rather than being composed primarily of nitrogen and oxygen (~78% and 21% respectively, with trace gases making up the rest), Earth’s early atmosphere was a combination of carbon dioxide and methane. And then, roughly 2.9 to 3 billion years ago, photosynthesizing bacteria appeared that began to enrich the atmosphere with oxygen gas.
Factors - Earth - Great - Oxidation - Event
Because of this and other factors, Earth experienced what is known as the “Great Oxidation Event” about 2.3 billion years ago, which permanently altered our planet’s atmosphere. Despite this general consensus, the process and timeline in which organisms evolved to convert sunlight into chemical energy using chlorophyll remains the subject to...
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