Panspermia

Panspermia () is the hypothesis that life exists throughout the Universe, distributed by space dust, meteoroids, asteroids, comets, and planetoids, as well as by spacecraft carrying unintended contamination by microorganisms. Panspermia is a fringe theory with little support amongst mainstream scientists. Critics argue that it does not answer the question of the origin of life but merely places it on another celestial body. It is also criticized because it cannot be tested experimentally. Panspermia proposes that microscopic lifeforms which can survive the effects of space (such as extremophiles) can become trapped in debris ejected into space after collisions between planets and small Solar System bodies that harbor life. Panspermia studies concentrate not on how life began but on methods that may distribute it in the Universe. Pseudo-panspermia (sometimes called soft panspermia or molecular panspermia) is the well-attested hypothesis that many of the pre-biotic organic building-blocks of life originated in space, became incorporated in the solar nebula from which planets condensed, and were further—and continuously—distributed to planetary surfaces where life then emerged. The first mention of panspermia was in the writings of the fifth-century BC Greek philosopher Anaxagoras. Panspermia began to assume a more scientific form through the proposals of Jöns Jacob Berzelius (1834), Hermann E. Richter (1865), Kelvin (1871), Hermann von Helmholtz (1879) and finally reaching the level of a detailed scientific hypothesis through the efforts of the Swedish chemist Svante Arrhenius (1903). Fred Hoyle (1915–2001) and Chandra Wickramasinghe (born 1939) were influential proponents of panspermia. In 1974 they proposed the hypothesis that some dust in interstellar space was largely organic (containing carbon), which Wickramasinghe later proved to be correct. Hoyle and Wickramasinghe further contended that life forms continue to enter the Earth's atmosphere, and may be responsible for epidemic outbreaks, new diseases, and the genetic novelty necessary for macroevolution.