Panspermia

Panspermia is the hypothesis that the seeds of life are prevalent throughout the universe, and furthermore that life on Earth began by such seeds landing on Earth and propagating themselves. The idea has its origins in the writings of Anaxagoras, but was first proposed in its modern form by Hermann von Helmholtz in 1879. Panspermia can be said to be either interstellar (between star systems) or interplanetary (between planets in the same solar system). There is as yet no compelling evidence to support or contradict it, although the consensus view holds that panspermia?especially in its interstellar form?is unlikely given the challenges of survival and transport in space.

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Sir Fred Hoyle (1915–2001) and Chandra Wickramasinghe were important proponents of the hypothesis who further contended that lifeforms continue to enter the Earth's atmosphere, and may be responsible for epidemic outbreaks and new diseases.

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Panspermia does not remove the need for life to originate somewhere, but does extend the time frame and environments available. Similarly it does not necessarily suggest that life originated only once and subsequently spread through the entire Universe, but instead that once started it may be able to spread to other environments suitable for replication. The mechanisms proposed for interstellar panspermia are theoretical and currently unproven. Interplanetary transfer of material is well documented, as evidenced by meteorites of Martian origin found on Earth. However, claims that these carry evidence of extraterrestrial lifeforms - let alone viable dormant lifeforms - have either been proven unfounded as a result of terrestrial contamination, misinterpretation, or hoaxing; or are currently hotly disputed. Interestingly, space probes may also be a viable transport mechanism for interplanetary panspermia in our Solar System (or even beyond) especially as terrestrial bacteria were shown to have survived in a dormant state on the Moon. Since then, however, NASA has implemented strict abiotic procedures to avoid planetary contamination.

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Exogenesis is a related, but less radical, hypothesis that simply proposes life originated elsewhere in the universe and was transferred to Earth, with no prediction about how widespread life is. The term "panspermia" is more well-known, however, and tends to be used in reference to what would properly be called exogenesis, too.

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Hypothesis: A hypothesis (assumption in ancient Greek) is a proposed explanation for a phenomenon. A scientific hypotheses must be testable and based on previous observations or extensions to scientific theories ....

Life: :For other uses, see Life and Living...

Universe: The universe is the whole spacetime continuum in which we exist, together with all the energy and matter within it. Attempts to understand the universe in this sense, on the largest possible scales, are made in cosmology, a science that has grown from physics and astronomy. During the second half of...