Panspermia

Panspermia is the general hypothesis that microorganisms, spores, or bacteria attached to tiny particles of matter have diffused through space, eventually encountering a suitable planet and initiating the rise of life there. The word itself means “all-seeding”. It is the theory that life on Earth did not originate here, but arrived from the depths of space. It originated with Svante Arrhenius, who in 1908 suggested that light from stars could blow microscopic germs from a world orbiting one star to another world orbiting another star. Panspermia never met with much support, but the idea never quite disappeared, and was rekindled in 1996 when a team of NASA scientists claimed to have found evidence for the presence of fossilized ancient microorganisms in a Martian meteorite.

Computer models have shown that rocks launched from Mars by a large meteorite impact can immediately enter Earth-crossing orbits if they are ejected just marginally faster than Mars’ escape velocity, and that about 1 in 10 million of Martian meteorites that reach the Earth may have spent less than half a Martian orbital period, about one year, in space. Any microorganisms aboard such meteorites might just have survived the rigors of space travel and entry through Earth’s atmosphere (microorganisms known as extremophiles are now known to have extraordinary survival attributes). Over the lifetime of the Solar System, the inner planets are calculated to have exchanged tens of thousands of tons of material in this way.

Fred Hoyle and N. Chandra Wickramasinghe have reformulated the idea of Panspermia to suggest that life was brought to the Earth by a comet, and that interstellar dust ‘grains’ have a bacterial component. Their main argument is that the origin and evolution of life involves too many steps, each in itself inherently improbable, to have happened on Earth – instead, it needs all the ‘resources of space’. Life will be carried around, mainly by comets, and take root wherever conditions are suitable.

Evidence is growing that the composition of giant molecular clouds, particularly in star-forming regions, is far richer that previously supposed. Whether or not any pre-biotic molecules that are formed survive long enough to be incorporated subsequently in planets orbiting newborn stars is not yet clear. However, only a tiny amount of such pre-biotic material needs to survive to seed planets with the chemical basis of life. Life is more likely to have disseminated in this manner than by the transfer of living organisms by Panspermia. Panspermia theories have, however, received support from the detection in 2001 of microorganisms in the stratosphere, at a height of 41 km (25 mi).

Questions to Ponder

• Is there any evidence to support the theory of Panspermia?
• If Panspermia is true, shouldn’t the process be going on even now?