Panspermia

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Panspermia is a theory (more directly described as a hypothesis, as there is no compelling evidence yet available to support or contradict it) that suggests that the seeds of life are prevalent throughout the universe and life on Earth began by such seeds landing on Earth and propagating. The theory has origins in the ideas of Anaxagoras, a Greek philosopher.

An important proponent of the theory was the British astronomer Sir Fred Hoyle. Hoyle's advocacy is both a blessing and a curse; although he was a highly original thinker and won top scientific accolades, some of his principal ideas such as steady state theory have been largely shown to be false. His science fiction writing also makes it easy for critics to discredit theories of extraterrestrial life.

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Evidence and mechanisms

There is some evidence to suggest that bacteria may be able to survive for very long periods of time even in deep space (and may therefore be the underlying mechanism behind Panspermia). Recent studies out of India have found bacteria at heights greater than 40 km in Earth's atmosphere where mixing from the lower atmosphere is unexpected, while Streptococcus mitus bacteria that had accidentally been taken to the moon on the Surveyor 3 spacecraft in 1967, could easily be revived after being taken back to earth 31 months later. However, a consequence of panspermia is that life throughout the universe would have a surprisingly similar biochemistry, being derived from the same ancestral stock. So the high-altitude bacteria might be expected, whether of earth or extra-terrestrial origin, to have a biochemistry similar to terrestrial forms. This is not resolvable until life on another planet can have its chemistry analysed.

Another objection to Panspermia is that bacteria would not survive the immense heat and forces of an impact on earth; no conclusions (whether positive or negative) have yet been reached on this point.

Suggestive evidence in favour of panspermia are

  • The remarkably rapid appearance of life on Earth in the fossil record. The earliest evidence is of fossilised stromatolites or bacterial aggregates, which are dated at only 3.8 billion years old -- only 500 million years after the oldest dated rocks. On some models of planet formation this is almost too soon for the Earth to have cooled sufficiently to allow liquid water and support life.
  • Bacteria and more complex organisms have been found in more extreme environments than thought possible, such as black smokers or oceanic volcanic vents. Some extremophile bacteria have been found living at temperatures above 100C, others in strongly caustic environments.
  • Bacteria which don't rely on photosynthesis for energy. In particular, endolithic bacteria using chemosynthesis found inside rocks and in subterranean lakes.
  • Semi-dormant bacteria found in ice cores over a mile beneath the antarctic - this lends credibility to the concept of sustaining the components of life on the surface of icy comets.
  • Inconclusive results from the Viking program biological tests. Tests were performed to detect the metabolism of radioactive elements by soil microbes on Mars, and then similar tests performed after the sample was raised to very high temperatures to kill any life. The tests were consistent with the presence of life, but the official NASA stance is that the effect was chemical rather than biological.
  • More than suggestive, these papers show strong evidence that life can be brought to earth via comets: http://education.vsnl.com/godfrey/ . These papers describe spores with a strange biology (they metabolize a wide variety of organic and inorganic materials) and no DNA, which came down in the red rain after a possible comet explosion near Kerala, India in 2001.
  • In 2002, the discovery of glycine (the simplest amino acid) in interstellar clouds lends additional support. [1]
  • Of material definitely known to originate off-earth, analysis of the rock sample known as ALH84001, generally regarded as originating on Mars, suggests it contains artifacts that may have been caused by life forms.

These are the only indication of extraterrestrial life to date and most are still widely disputed.

Some have taken the theory as an answer to those arguing the improbability of the origin of life, in that wherever life first began, it spread throughout the universe by panspermia. However, panspermia doesn't alleviate the need for life to have started somewhere at some time, it merely extends the time frame and environments available for life to originate.

Some believers in panspermia, however, believe that life never evolved from inorganic molecules, but that it has existed as long as all other forms of matter. This is an extension of panspermia called cosmic ancestry.

Directed Panspermia

A second prominent proponent of panspermia is Nobel prize winner Francis Crick, along with Leslie Orgel who proposed the theory of directed panspermia in 1973. This suggests that the seeds of life may have been purposely spread by an advanced extraterrestrial civilisation. Crick argues that small grains containing DNA, or the building blocks of life, fired randomly in all directions is the best, most cost effective strategy for seeding life on a compatible planet at some time in the future. The strategy might have been pursued by a civilisation facing catastrophic annihilation, or hoping to terraform planets for later colonisation.

Science Fiction

The theory of panspermia has been explored in a number of works of science fiction, notably Jack Finney's Invasion of the Body Snatchers (twice made into a film) and the Dragonriders of Pern books of Anne McCaffrey. In John Wyndham's book, The Day of the Triffids, the first person narrator, writing in historical mode, takes care to reject the theory of panspermia in favour of the conclusion that the eponymous carnivorous plants are a product of Soviet biotechnology.

Some works of science fiction advance a derivative of the theory as a rationalisation for the improbable tendency of fictional extra-terrestrials to be strongly humanoid in form as well as living on earth-compatible worlds (see Class M planet).

See also

Further reading

  • Fred Hoyle, The Intelligent Universe, Michael Joseph Limited, London 1983, ISBN 0718122984
  • Francis Crick, Life, Its Origin and Nature, Simon and Schuster, 1981, ISBN 0708822355

External links


References

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