Earth is the only planet in the universe known to harbour life. The Drake equation has been used to estimate the probability of life elsewhere, but scientists disagree on many of the values of variables in this equation (although strictly speaking Drake equation estimates relate the number of extraterrestrial civilizations in our galaxy with which we might come in contact - not probability of life elsewhere). Depending on those values, the equation may either suggest that life arises frequently or infrequently. Drake himself estimated the number of civilizations in our galaxy with which we might expect to be able to communicate at any given time as equal to one.
Relating to the origin of life on Earth, panspermia and exogenesis are theories proposing that life originated elsewhere in the universe and was subsequently transferred to Earth perhaps via meteorites, comets or cosmic dust. For example, there is the meteorite ALH84001. However those theories do not help explain the origin of this extraterrestrial life.
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