Panspermia (Greek: πανσπερμία from πᾶς/πᾶν (pas/pan) "all" and σπέρμα (sperma) "seed") is the hypothesis that "seeds" of life exist already all over the Universe, that life on Earth may have originated through these "seeds", and that they may deliver or have delivered life to other habitable bodies. The related but distinct idea of exogenesis (Greek: ἔξω (exo, "outside") and γένεσις (genesis, "origin")) is a more limited hypothesis that proposes life on Earth was transferred from elsewhere in the Universe but makes no prediction about how widespread it is. Because the term "exogenesis" is more well-known, it tends to be used in reference to what should strictly speaking be called panspermia.
Hypothesis.
The first known mention of the term was in the writings of the 5th century BC Greek philosopher Anaxagoras. In the nineteenth century it was again revived in modern form by several scientists, including Jöns Jacob Berzelius (1834), Kelvin (1871), Hermann von Helmholtz (1879) and, somewhat later, by Svante Arrhenius (1903). There is as yet no evidence to support or contradict panspermia, although the majority view holds that panspermia – especially in its interstellar form – is unlikely given the challenges of survival and transport in space. Sir Fred Hoyle (1915–2001) and Chandra Wickramasinghe (born 1939) 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, new diseases, and the genetic novelty necessary for macroevolution. Panspermia 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.
Proposed mechanisms
The mechanisms proposed for interstellar panspermia are hypothetical and currently unproven. Panspermia can be said to be either interstellar (between star systems) or interplanetary (between planets in the same star system), and its transport mechanisms may include radiation pressure and lithopanspermia (microorganisms in rocks). Deliberate directed panspermia from space to seed Earth or sent from Earth to seed other solar systems have also been proposed. One new twist to the hypothesis by engineer Thomas Dehel (2006), proposes that plasmoid magnetic fields ejected from the magnetosphere may move the few spores lifted from the Earth's atmosphere with sufficient speed to cross interstellar space to other systems before the spores can be destroyed.
Interplanetary transfer of material is well documented, as evidenced by meteorites of Martian origin found on Earth. Space probes may also be a viable transport mechanism for interplanetary cross-pollination in our solar system or even beyond. However, space agencies have implemented sterilization procedures to avoid planetary contamination.
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