Princeton University researchers Edward Belbruno and Amaya Moro-Martín, said that under certain conditions "there is a high probability that life came to Earth --or spread from Earth to other planets --during the solar system's infancy when Earth and its planetary neighbors orbiting other stars would have been close enough to each other to exchange lots of solid material." The research is based on computer simulations of the star cluster that gave forth our Sun and backs up a theory known as "weak transfer" in which solid objects can gradually meander out of the orbit of one object and into another. The simulations greatly increase the odds that the process known as "lithopanspermia" could have happened, the researchers said.
Lithopanspermia the hypothesis that basic life forms are distributed throughout the universe via meteorite-like planetary fragments blown out by disruptions such as volcanic eruptions and collisions with objects such as asteroids. The theory holds that eventually, another planetary system's gravity trapped these roaming rocks, which could have resulted in a mingling that transferred living cargo."