A study by American and Spanish astrobiologists details a newly discovered process called “weak transfer” that suggests microbe-laden rocks from Earth could have traveled out of our solar system and spawned life in other galaxies. The study proposes not only that human life could have originated on Earth, but also that Earth could have been the impetus for life on other planets.

Weak transfer works like this: a slow-moving rock fragment travels to the outer edge of Earth’s gravitational pull and launches back into space, floating freely until it’s pulled in by another planetary system. Researchers say that planet could be something like Mars — or a planet in an entirely different solar system. The process also proves that the opposite could be true: a microbe-covered fragment from another planet could have crashed down onto Earth, sparking the onset of human existence here. Researchers estimate that anywhere between 100 trillion and 30 quadrillion fragments could have been exchanged between our solar system and our neighboring solar system, with as many as 200 billion of those rocks originating from Earth.

The only time in history when this phenomenon was possible was between 164 million to 288 million years after the formation of the solar system, according to the study. For any of this to point to Earth as the springboard for life in other solar systems, life on Earth would have had to be present 3.8 billion years ago when the conditions for weak transfer were right. Science currently clocks the first appearance of microorganisms on Earth at about 3.6 billion years ago.

The weak transfer theory is one of several proposed by scientists to answer the age-old mystery surrounding the origin of human life. Other popular hypotheses and beliefs used to explain the spark of life include that life originated when aliens landed on Earth, human life occurred spontaneously, or that it originated from God.

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