Most scientists are in agreement that the dinosaurs were wiped out by a 6-mile (10-kilometer) wide asteroid that smashed into the Earth 65 million years ago. The asteroid's impact in what is today Mexico had numerous consequences, not the least of which was the mass extinction of almost all land-based life on Earth. But the dinosaurs weren't the only life forms affected by the force equivalent of a billion atomic bombs literally turning the sky black. Microbes living on rocks were flung far into space as a result of the impact. Whether these microbes could have survived an interstellar trip is unknown, but simulations of Earth ejecta conducted last year have placed potentially life-seeding rocks as far as Jupiter. Astrobiologists estimate that the sturdiest of microbial life forms could survive up to 30,000 years in space, which would be long enough for a journey to another life-sustaining planetary body (perhaps an ocean-bearing moon).
A more recent study from astrobiologists in Japan sought to calculate how much of Earth's mass could have potentially reached moons or planets fit for life, including the moons of Jupiter and Saturn, and even exoplanets orbiting nearby stars. By estimating how much ejecta was flung into space 65 million years ago (we're talking billions of tons), scientists at Kyoto Sangyo University calculate that about a thousand microbe-housing Earth rocks could have even reached a red dwarf star 20 light years away, which is thought to have an Earth-like planet within its habitable zone. And if microbial life could survive that journey, the scientists say, then there's no reason why they couldn't flourish in alien environments. Life will find a way--we'll just have to check back in a few million years to see how far it's gone.