Science is the act of making a guess and comparing that guess against reality, which results in some amazing experiments. The guess: that life on earth came from bacteria laden asteroids and meteors. The test: could bacterial spores survive such a ride. The results:

Even if extraterrestrial life did exist, proponents of the panspermia theory must still determine how life arrived on Earth. The best candidates to act as “seeds of life” are bacterial spores, which allow bacteria to remain in a dormant state in the absence of nutrients. Bacteria constitute about one-third of Earth’s biomass and are characterized by their ability to survive under extreme conditions—those that we initially believed were unable to support life. In light of panspermia, the important question is if bacteria or bacterial spores could survive in space.

To address this question, scientists at the German Aerospace Centre in Cologne designed experiments using the Russian FOTON satellite. They mixed bacterial spores with particles of clay, red sandstone, Martian meteorite or simulated Martian soil to make small lumps a centimeter across. The lumps were then exposed via the satellite to outer space. After two weeks of exposure, researchers found that nearly all of the bacterial spores mixed with red sandstone were able to survive. Another study showed that bacterial spores could survive the extreme conditions of outer space for six years if they were protected from extraterrestrial solar UV radiation. This would be possible if the spores traveled within comets or meteorites.