Everyone knows that we as humans literally owe the air we breathe to the greenery around us. As school children we learned that plants (as well as algae and cyanobacteria) perform the all-important biological "magic trick" known as photosynthesis, which helps generate the atmospheric oxygen we take in with every breath.
Plants, algae and cyanobacteria alter our planet in a way that only life can: they use photosynthesis to completely change the composition of the Earth's atmosphere. Since the days when dust devils on Mars were suspected to be the seasonal variation of vegetation, photosynthesis has been considered a key to identifying the presence of life on other planets.
Both atmospheric oxygen (in the presence of liquid water) and the reflectance spectrum of plant leaves produce signs of life — dubbed "biosignatures" — that can be seen from space. Therefore, photosynthetic biosignatures are a priority in the search for life on planets in distant solar systems. The big question is, will extrasolar photosynthesis use the same pigment as on Earth?
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