The "exoplanet" revolution of the last 20 years has shown us that the universe is awash in alien worlds. More exciting, we now have methods where the atmospheres of those worlds may provide indirect evidence — called "bio-signatures" — for the existence of life.
"Its possible that when we survey planets we may find artifacts of dead civilizations that aren't around anymore," said Harvard astrophysicist Avi Loeb. "We humans are probably not special," Loeb added, explaining that with so many planets in the universe, the rise of civilizations may not be so usual.
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