The task of astrobiologists who seek evidence for extrasolar microbes is as simple as imitation. Primitive forms of extraterrestrial life should exist under physical conditions that were nurtured in natural environments similar to those on Earth. Hence, astrobiologists plan to search for the molecular products of microbes-as-we-know-them on rocky exoplanets with atmospheres in the habitable zone of their host stars.
Conducting an honsest and serious search here on Earth would be far easier and more productive.
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