Panspermia, meaning “all-seeding,” is the idea that organic molecules are in space and that microorganisms, spores, or bacteria attached to tiny particles of matter can travel through space, and in theory, eventually land on a suitable planet and initiate the rise of life there. The first known mention of the term was by the Greek philosopher Anaxagoras (c. 5 B.C.E.). The idea was revived in the nineteenth century by several scientists of the time, including the British scientist Lord Kelvin (1824–1907), who suggested that life may have arrived here from outer space, perhaps carried by meteorites. In 1903, the Swedish chemist Svante Arrhenius (1859–1927) put forward the more complex idea that life on Earth was “seeded” by means of extraterrestrial spores, bacteria, and microorganisms coming here on tiny bits of cosmic matter. In 1974, British astronomer Sir Fred Hoyle (1915–2001) and Sri Lankan-born British mathematician Chandra Wick-ramasinghe (1939–) proposed that dust in interstellar space contained carbon, noting that even today, life forms continue to enter the Earth’s atmosphere (they also said these organics may be responsible for new diseases or epidemic outbreaks).

The theory further suggests that, based on life forms scientists have discovered on Earth that can withstand the rigors of extreme environments, life such as bacteria could travel dormant in space for an extended period. They could eventually collide with planets or intermingle with protoplanetary disks (broken-up chunks of rock and debris that eventually form a solar system), with the bacteria (or other life) eventually becoming active. But note: panspermia is not meant to mean how life began, but is the method that may cause its ability to survive and spread.