The theory that meteorites carrying bacteria kickstarted life on Earth has been strengthened by a German experiment that placed bugs in orbit to see if they survived the brutal environment of space. The Swedish chemist Svante Arrhenius proposed the theory in 1903, contending that billions of years ago, bacteria drifting through the cosmos landed in the fertile soil of Earth, where they flourished and evolved into higher forms of life. Critics of Arrhenius’s so-called pan-spermia theory say that unprotected bacterial hitchhikers would have been slaughtered by cosmic rays and ultraviolet radiation from the Sun. The argument has raged back and forth, spiced by contemporary research into rocks that were knocked off the surface of Mars, presumably by some asteroidal collision, and eventually landed on Earth as meteorites.
