Astrobiology: The Living Universe
A theory called panspermia states that the Earth was "seeded" with life when celestial objects collided with the Earth. The term panspermia is Greek for ‘seeds everywhere’. While the idea of life on Earth having originated elsewhere in the galaxy had been discussed by ancient greek philosophers, the modern theory of panspermia did not gain much approval until the late twentieth century. At this time, astronomers Fred Hoyle and Chandra Wickramasinghe found traces of organic compounds in the interstellar medium by analyzing the light from distant stars. This evidence supported the theory that comets (composed primarily of water and ice) and other celestial objects could carry bacterial spores across galaxies.