Panspermia
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'''Panspermia''' ([[Greek language|Gk]]. πάς/πάν (pas/pan, all) 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.
'''Exogenesis''' ([[Greek language|Gk]]. "outside 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 "panspermia" is more well-known, it tends to be used in reference to what would properly be called exogenesis.
The hypothesis is notable as a topic in [[science-fiction]] and quasi-religious circles such as [[Raëlism]].{{Fact|date=February 2008}}
== Hypothesis ==
The first known mention of the idea was in the writings of the [[5th century BC]] [[Ancient Greece|Greek]] philosopher [[Anaxagoras]].{{Fact|date=September 2007}} The panspermia hypothesis was dormant until 1743 when it appeared posthumously in the writings of [[Benoît de Maillet]], who suggested that germs from space had fallen into the oceans and grown into [[fish]] and later [[amphibian]]s, [[reptile]]s and then [[mammal]]s{{Fact|date=July 2008}}. In the nineteenth century it was again revived in modern form by several scientists, including [[Jöns Jacob Berzelius]] (1834),<ref> {{Citation | last = Berzelius (1799-1848) | first = J. J. | title = Analysis of the Alais meteorite and implications about life in other worlds.}} </ref> [[William Thomson, 1st Baron Kelvin|Kelvin]] (1871),<ref> {{Citation | last = Thomson (Lord Kelvin) | first = W. | title = Inaugural Address to the British Association Edinburgh. “We must regard it as probably to the highest degree that there are countless seed-bearing meteoritic stones moving through space.” | journal == Nature | volume = 4 | pages = 262 | year = 1871}} </ref> [[Hermann von Helmholtz]] (1879) and, somewhat later, by [[Svante Arrhenius]] (1903). Panspermia can be said to be either interstellar (between star systems) or interplanetary (between planets in the same star system). Mechanisms for panspermia include radiation pressure (Arrhenius) and lithopanspermia (microorganisms in rocks) (Kelvin).<ref> {{Citation | last = Weber | first = P | last2 = Greenberg| title =“Can spores survive in interstellar space?” | journal = Nature | volume = 316 | pages = 403–407 | year = 1985| doi =10.1038/316403a0| unused_data =|first 2 = J. M. }} </ref><ref> {{Citation | last = Melosh | first = H. J. | title = “The rocky road to panspermia” | journal = Nature | volume = 332 | pages = 687–688 | year = 1988 | doi = 10.1038/332687a0}} </ref> Directed panspermia from space to seed Earth (Orgel and Crick, 1973)<ref> {{Citation | last = Crick | first = F. H. | last2 = Orgel | first2 = L. E.| title = Directed Panspermia | journal = Icarus | volume = 19 | pages = 341–348 | year = 1973| doi = 10.1016/0019-1035(73)90110-3}} </ref> or sent from Earth to seed other solar systems (Mautner 1979, 1997)<ref> {{Citation | last = Mautner | first = M | last2 = Matloff | title = "Directed panspermia: A technical evaluation of seeding nearby solar systems." | journal = J. British Interplanetary Soc. | volume = 32 | pages = 419 | date = 1979 | year = 1979 | unused_data = |first 2 = G.}} </ref><ref> {{Citation | last = Mautner | first = M. N. | title = “Directed panspermia. 3. Strategies and motivation for seeding star-forming clouds” | journal = J. British Interplanetary Soc. | volume = 50 | pages = 93 | year = 1997 }} </ref> has also been proposed.
There is as yet no compelling evidence to support or contradict it, although the majority view holds that panspermia — especially in its interstellar form — is unlikely given the challenges of survival and transport in space. One new twist to the theory by engineer Thomas Dehel (2006) proposes that plasmoids 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. <ref>[http://space.newscientist.com/article/dn9601-electromagnetic-space-travel-for-bugs.html Electromagnetic space travel for bugs? - space - 21 July 2006 - New Scientist Space<!-- Bot generated title -->]</ref> <ref>http://adsabs.harvard.edu/abs/2006cosp...36....1D</ref>
[[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]]. This extension has also been adopted by proponents of [[Cosmic ancestry]].
Panspermia ''per se'' 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. (In the strongest version of panspermia, life never originated, but always existed — this axiom would require amending the [[big bang]] theory.) The mechanisms proposed for interstellar panspermia are hypothetical and currently unproven. Interplanetary transfer of material is well documented, as evidenced by [[Mars meteorite|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.{{Fact|date=September 2007}}
Interestingly, [[space probe]]s may also be a viable transport mechanism for interplanetary cross-pollination in our solar system (or even beyond). However, NASA has implemented strict abiotic procedures to avoid planetary contamination.
== Evidence ==
Until a large portion of the galaxy is surveyed for signs of life or contact is made with other civilizations, the panspermia hypothesis in its fullest meaning will remain difficult to test. There is, however, [[circumstantial evidence]] for exogenesis:
=== Narrow time window for geogenesis ===
[[Image:Stromatolites.jpg|thumb|right|[[Pre-Cambrian]] [[stromatolites]] in the Siyeh Formation, [[Glacier National Park (U.S.)|Glacier National Park]]. It is in formations such as this that 3.5 billion year old [[fossilized]] [[algae]] microbes, the earliest known life on earth, were discovered.]]
The [[Precambrian]] [[fossil]] record indicates that life appeared soon after the Earth was formed. This would imply that life appears within several hundred million years when conditions are favourable.
* Generally accepted scientific estimates of the [[age of the Earth]] place its formation (along with the rest of the [[Solar system]]) at about 4.55 [[Giga-annum|Ga]].
* The oldest known [[sedimentary rock]]s are somewhat altered [[Hadean]] formations from the southern tip of [[Akilia island]], West [[Greenland]]. These rocks have been dated as no younger than 3.85 Ga. The Greenland sediments include [[banded iron bed]]s, thought to be the result of oxygen released by [[photosynthetic]] organisms combining with dissolved iron to form insoluble iron oxides. Carbon deposits in the rock show low levels of [[carbon-13]]. [[Kerogen]] deposits (derived from organic matter) are [[stable isotope|isotopically]] light (i.e. more negative δ<sup>13</sup>C values) which is indicative of [[photosynthesis]] (see Schidlowski, 1988). However, this interpretation is under doubt as the Akilia rocks have undergone high-temperature [[metamorphic rock|metamorphosis]] which is known to be [[isotopic fractionation|fractionating]] itself (Gilmour & Wright, 1997). There is also a lack of corroborating [[sulfur#Isotopes|sulphur isotope]] fractionation (Nisbet, 2000). Both the sedimentary origin and the carbon content of the rocks have been questioned (Lepland et al, 2005).
* Fossilized [[stromatolite]]s or [[bacterium|bacteria]]l aggregates, the oldest of which are dated at 3.5 billion years old, suggest that photosynthesis might be exogenic. The bacteria that form stromatolites, [[cyanobacteria]], are photosynthetic. Most models of the [[origin of life]] have the earliest organisms obtaining energy from [[reduced]] chemicals, with the more complex mechanisms of photosynthesis evolving later.
* During the [[Late Heavy Bombardment]] of the Earth's [[Moon]] about 3.9 Ga (as evidenced by [[Project Apollo|Apollo]] lunar samples) impact intensities may have been up to 100x those immediately before or after (Cohen et al., 2000). From analysis of lunar melts and observations of similar cratering on [[Mars#Topography|Mars' highlands]], Kring and Cohen (2002) suggest that the LHB was caused by [[asteroid]] impacts that affected the entire inner [[solar system]]. This is likely to have effectively sterilised Earth's entire planetary surface, including submarine [[hydrothermal vent|hydrothermal systems]] that would be otherwise protected (Cohen et al., 2000).
* The best estimate of the origin of the Universe, from the [[Wilkinson Microwave Anisotropy Probe]], is 13700 million years ago (13.7 Ga). However, at least one subsequent cycle of star birth/death is required for [[Stellar nucleosynthesis|nucleosynthesis]] of the [[Carbon|C]], [[Nitrogen|N]] and [[Oxygen|O]] essential to life, and this process may have taken up to several Ga to produce sufficient quantities (Gilmour et al., 1997). This puts the earliest possible emergence of life in the Universe at ~12.7 Ga, although there is large uncertainty in the length of the necessary time period.
If life originated on Earth it did so in a window of at most 1 Ga (4.55 Ga to 3.5 Ga), most plausibly 400 Ma (3.9 Ga to 3.5 Ga), and possibly <100 Ma (3.9 Ga to 3.85 Ga) if the Greenland (3.85 Ga) isotope signal is correct. If life originated elsewhere, the window expands to ~9 Ga. That full length of time might not be available on a single planet, but the Earth has provided a life-friendly environment for at least 3.5 Ga.
=== Extremophiles ===
Evidence has accumulated that some bacteria and [[archaea]] are more resistant to extreme conditions than previously recognized, and may be able to survive for very long periods of time even in deep space. These [[extremophile]]s could possibly travel in a dormant state between environments suitable for ongoing life such as planetary surfaces.
* Bacteria and more complex organisms have been found in more extreme environments than thought possible, such as [[black smoker]]s or oceanic volcanic vents. Some extremophile bacteria have been found living at temperatures above 100 [[Celsius|°C]]; A study revealed that a fraction of bacteria survive heating pulses up to 250 degrees C in vacuum, while similar heating at normal atmospheric pressure leads to the total sterilization of samples.<ref>Can microorganisms survive upon high-temperature heating during the interplanetary transfer by meteorites? Biofizika. 2007 Nov-Dec;52(6):1136-40 [http://www.ncbi.nlm.nih.gov/pubmed/18225667?ordinalpos=6&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum]</ref> Other bacteria can thrive in strongly [[Causticity|caustic]] [[environment (biophysical)|environment]]s, and others at extreme pressures 11 km under the ocean.<ref>[http://news.bbc.co.uk/2/hi/science/nature/4235979.stm BBC NEWS | Science/Nature | Life flourishes at crushing depth<!-- Bot generated title -->]</ref>
* Semi-dormant bacteria found in [[ice core]]s over a mile beneath the [[Antarctic]] lends credibility to the idea that the components of life might survive on the surface of icy comets.
* There are bacteria that do not rely on photosynthesis for energy. In particular, [[endolith]]ic bacteria using [[chemosynthesis]] have been found inside rocks and in subterranean lakes.
* ''[[Deinococcus radiodurans]]'' is a [[radioresistant]] bacterium that can survive high radiation levels.
* Dormant bacteria have been isolated from insects in amber 10s [[Annum|Ma]] old.<ref>[http://findarticles.com/p/articles/mi_m1200/is_n20_v147/ai_17128688 Ancient bacteria brought back to life]</ref>
* Recent experiments suggest that if bacteria were somehow sheltered from the radiation of space, perhaps inside a thick meteoroid, they could survive dormant for millions of years.
* Duplicating the harsh conditions of cold interstellar space in their laboratory, NASA scientists have created primitive cells that mimic the membranous structures found in all living things. These chemical compounds may have played a part in the origin of life.<ref>[http://astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=122&mode=thread&order=0&thold=0 Scientists Find Clues That Life Began in Deep Space :: Astrobiology Magazine - earth science - evolution distribution Origin of life universe - life beyond :: Astrobiology is study of earth science evolution distribution Origin of life in universe terrestrial<!-- Bot generated title -->]</ref>
===Spores===
[[Spores]] are another potential vector for transporting life through inhospitable and inimical environments, such as the depths of interstellar space. Spores are produced as part of the normal life cycle of many [[plant]]s, [[algae]], [[fungus|fungi]] and some [[protozoan]]s,<ref>[http://www.pollenplus.com/spores/faq.html Spore FAQ - Aerobiology Research Laboratory<!-- Bot generated title -->]</ref> and some bacteria produce [[endospores]] or [[Microbial cyst|cysts]] during times of stress. These structures may be highly resilient while metabolically inactive, and some can function when favorable conditions are restored after exposure to radiation, temperature extremes, desiccation, or other conditions fatal to the parent organism.
=== Wider range of potential habitats for life ===
Another line of evidence comes from research that shows there are many more potential habitats for life than Earth-like planets.
* The presence of past liquid water on Mars, suggested by river-like formations on the red planet, was confirmed by the [[Mars Exploration Rover]] missions. In December of 2006, [[Michael C. Malin]] of [[Malin Space Science Systems]] published a paper in the journal [[Science (journal)|Science]] which argued that his camera (the Mars Observer Camera) had found evidence suggesting water was occasionally flowing on the surface of Mars within the last five years.
* Water oceans might exist on [[Europa (moon)|Europa]], [[Enceladus (moon)|Enceladus]], [[Triton (moon)|Triton]] and perhaps other moons in the Solar system. Even moons that are now frozen ice balls might earlier have been melted internally by heat from radioactive rocky cores. Bodies like this may be extremely common throughout the Universe. [[Lake Vostok]] in [[Antarctica]], which has been sealed for millions of years, and which may contain unusual life or be sterile, is a possible testing ground for ways to explore these moons.
* Bacteria have been discovered living within warm rock deep in the Earth's crust.
=== Evidence of extraterrestrial life ===
Although clearly speculative, the majority view in the scientific community seems to be an acceptance that the existence of life elsewhere in the Universe is highly probable due to the sheer number of potential sites where life could take hold. Today's estimates of values for the [[Drake Equation]] suggest the probability of intelligent life in a single galaxy like our own [[Milky Way]] may be much smaller than once was thought while the sheer numbers of galaxies in our Universe make it seem inevitable somewhere nevertheless.<ref>See shrinking estimates of parameter values (since its inception in 1961) as discussed throughout the [[Drake equation]] article.</ref> Space travel over such vast distances would be limited to below the speed of light by the [[theory of relativity]] alone, taking such an incredibly long time to the outside observer, with vast amounts of energy required. Nevertheless small groups of researchers like the Search for Extra-Terrestrial Intelligence ([[SETI]]) continue to monitor the skies for transmissions from within our own galaxy at least.
Moreover, the expanded Drake equation of [[astrobiological]] proponents like the [[Rare Earth hypothesis]]ts reduces this probability further still. They argue that the conditions required for the evolution of complex [[multicellular life]] here on Earth – and therefore by extension intelligent life – may be exceedingly rare in the universe whilst simultaneously conceding that simple single-celled [[microorganisms]] might well be abundant.<ref>See citation for physicist Stephen Webb under the [[Rare Earth hypothesis]] article.</ref>
==== Still under investigation/undetermined ====
* The [[Red rain in Kerala|Red Rain of Kerala]]. In 2003, Satyanarayana et al. proposed that the rain was coloured red by a dust cloud from the [[Middle East|Persian Gulf]].<ref>[http://web.archive.org/web/20041028040513/www.indiaexpress.com/news/regional/kerala/20030619-0.html Mystery of Kerala's 'red rain' unraveled : Kerala News : IndiaExpress.Com<!-- Bot generated title -->]</ref> Their paper was then published in ''Aerosol Science and Technology''.<ref>http://taylorandfrancis.metapress.com/index/2FFTM2LX7D9A2AP5.pdf</ref> Dr. [[Godfrey Louis]] has analyzed the dust and reported finding spores that he has hypothesised are of extraterrestrial origin. In April 2006, Louis published his findings in [[Astrophysics and Space Science]].<ref>[http://www.springer.com/sgw/cda/frontpage/0,11855,4-10100-70-35683926-0,00.html Astrophysics and Space Science - Astronomy Journals, Books & Online Media | Springer<!-- Bot generated title -->]</ref><ref>[http://springerlink.metapress.com/openurl.asp?genre=article&doi=10.1007/s10509-005-9025-4 SpringerLink Home - Main<!-- Bot generated title -->]</ref><ref>[http://www.popsci.com/popsci/science/2c21c0f98d07b010vgnvcm1000004eecbccdrcrd.html Is It Raining Aliens? | Popular Science<!-- Bot generated title -->]</ref> Louis claimed that the red particles "reproduce plentifully", and that they did so even in "water superheated to nearly 300 °C".
[[Image:ALH84001 structures.jpg|right|thumb|Microstructures in [[ALH84001]] claimed to be of biogenic origin]]
* A [[meteorite]] originating from [[Mars (planet)|Mars]] known as [[ALH84001]] was shown in 1996 to contain [[microscopic]] structures resembling small terrestrial [[nanobacteria]]. When the discovery was announced, many immediately conjectured that the fossils were the first true evidence of [[extraterrestrial life]] — making headlines around the world, and even prompting [[President of the United States|U.S. President]] [[Bill Clinton]] to make a formal televised announcement to mark the event{{Fact|date=July 2008}}. As of 2003 however, most experts agree that these are not indicative of life, but may instead be formed abiotically from [[organic molecules]]. It has not yet conclusively been shown how they formed and recent advances in [[nanobe]] research has made the find interesting again.
* An Indian and British team of researchers led by Chandra Wickramasinghe reported evidence at the 46th annual meeting of the International Society for Optical Engineering (SPIE) in San Diego, California on April 29, 2001 that air samples gathered from the stratosphere by the Indian Space Research Organization contained clumps of living cells. Wickramsinghe calls this "unambiguous evidence for the presence of clumps of living cells in air samples from as high as 41 kilometers, well above the local tropopause, above which no air from lower down would normally be transported".<ref name="sciam_Wick">[http://www.sciam.com/article.cfm?articleID=000D499B-4662-1C60-B882809EC588ED9F Scientists Say They Have Found Extraterrestrial Life in the Stratosphere But Peers Are Skeptical: Scientific American]</ref> A reaction report at [[NASA Ames Research Center|NASA Ames]] indicated skepticism towards the premise that Earth life cannot travel to and reside at such altitudes, but noted that some microbes can remain dormant for millions of years, possibly long enough for an interplanetary voyage.<ref>[http://archives.cnn.com/2000/TECH/space/11/24/alien.microbe.claim/index.html CNN.com - Space - Scientists discover possible microbe from space - November 24, 2000<!-- Bot generated title -->]</ref> Max Bernstein, a space scientist associated with [[SETI]] and Ames, argues the results should be interpreted with caution, noting that "it would strain one's credulity less to believe that terrestrial organisms had somehow been transported upwards than to assume that extraterrestrial organisms are falling inward".<ref name="sciam_Wick" />
* On May, 2001, two researchers from the [[University of Naples Federico II|University of Naples]] claimed to have found live extraterrestrial bacteria inside a meteorite. Geologist Bruno D'Argenio and molecular biologist Giuseppe Geraci claim the bacteria were wedged inside the crystal structure of minerals, but were resurrected when a sample of the rock was placed in a culture medium. They believe that the bacteria were not terrestrial because they survived when the sample was sterilized at very high temperature and washed with alcohol. They also claim that the bacteria's DNA is unlike any on Earth.<ref>[http://space.newscientist.com/article/dn725 Alien visitors - 11 May 2001 - New Scientist Space<!-- Bot generated title -->]</ref> They presented a report on May 11, 2001, concluding that this is the first evidence of extraterrestrial life, documented in its genetic and morphological properties. Some of the bacteria they discovered were found inside meteorites that have been estimated to be over 4.5 [[Giga-annum|billion years]] old, and were determined to be related to modern day [[Bacillus subtilis]] and Bacillus pumilus bacteria on Earth but appears to be a different strain.<ref>http://www.lincei.it/pubblicazioni/rendicontiFMN/rol/pdf/S2001-01-04.pdf</ref>
* Narlikar et al. (2003) took air samples at 41 km over [[Hyderabad, India]] — above the [[tropopause]] where mixing from the lower atmosphere is unexpected — from which rod and coccoid bacteria were isolated. Two bacterial and one fungal species were later independently isolated from these filters which were identified as ''[[Bacillus simplex]]'', ''[[Staphylococcus pasteuri]]'' and ''[[Engyodontium album]]'' respectively (Wainwright, 2003).<ref>{{cite web |url=http://meghnad.iucaa.ernet.in/~jvn/FEMS.html |title=Microorganisms cultured from stratospheric air samples obtained at 41km |author=M. Wainwright, N.C. Wickramasinghe, J.V. Narlikar, P. Rajaratnam |accessdate=2007-05-11}}</ref> The experimental procedure suggested that these were not the result of laboratory contamination, although similar isolation experiments at separate laboratories were unsuccessful. That these are common terrestrial organisms is not necessarily contraindicative of panspermia, since a prediction of the hypothesis is that life throughout the Universe is derived from the same ancestral stock. Assuming they are not contaminants, did the micro-organisms come from the Earth or space? That there were no [[volcanic eruption]]s — the only known way for terrestrial particles to mix up beyond the tropopause — prior to sampling suggests against a terrestrial source. In either case, Wainright (2003) points out that some part of the panspermia hypothesis is validated: either terrestrial micro-organisms are indeed derived from space, or they are capable of contaminating our local space in a viable form. Measuring the isotope ratios of carbon and nitrogen in the micro-organisms from the stratosphere could reveal whether they come from Earth or space.
* Of three [[Viking biological experiments|biological experiments]] on the Mars lander [[Viking program|Viking]], two gave results that were initially indicative of life. However, the similar results from heated [[experimental control|controls]], how the release of indicative gas tapered off, and the lack of organic molecules in soil samples all suggest that the results were the result of an abiotic chemical reaction rather than biological metabolism. Later experiments showed that terrestrial [[clay]]s could reproduce the results of the two positive Viking experiments. Despite this, some of the Viking experiments' designers remain convinced that they are diagnostic for life.
====Widely discounted====
*A NASA research group found a small number of ''[[Streptococcus mitis]]'' bacteria living inside the camera of the [[Surveyor 3]] spacecraft when it was brought back to Earth by [[Apollo 12]]. They believed that the bacteria survived since the time of the craft's launch to the moon.<ref>{{cite web|url=http://www.lpi.usra.edu/lunar/missions/apollo/apollo_12/experiments/surveyor/|title=Apollo 12 Mission|publisher=Lunar and Planetary Institute|accessdate=2008-02-15}}</ref> However, these reports are no longer tenable: see [[Reports of Streptococcus mitis on the moon]].
* Over the past century thousands of people have reported [[UFO]] sightings in countries all over the world. Nevertheless, these reports have caused disagreements among experts as to their validity,<ref>http://66.102.9.104/search?q=cache:7-lUVtpyG0cJ:skepdic.com/ufos_ets.html+skepdic.com+ufos&hl=en&gl=uk&ct=clnk&cd=1</ref> and no widely accepted evidence has yet been published in mainstream scientific writings to suggest that intelligent alien species have ever visited the Earth.
==== Falsified ====
* In 1962, Claus ''et al.'' announced the discovery of 'organised elements' embedded in the [[Orgueil (meteorite)|Orgueil]] meteorite. These elements were subsequently shown to be either [[pollen]]s (including that of [[Senecio|ragwort]]) and [[fungus|fungal]] [[spore]]s (Fitch & Anders, 1963) that had contaminated the sample, or crystals of the mineral [[olivine]].
* In 2002, the discovery of [[glycine]] (the simplest [[amino acid]]) in [[cosmic dust|interstellar cloud]]s was reported.<ref>[http://physicsweb.org/article/news/7/8/7 Amino acid detected in space - physicsworld.com<!-- Bot generated title -->]</ref><ref>{{cite journal | last=Kuan | first=Y.-J. | coauthors=''et al.'' | title=Interstellar Glycine | year = 2003 | journal =Astrophysical Journal | volume=593 | issue=2 | pages=848–867 | url=http://adsabs.harvard.edu/abs/2003ApJ...593..848K | doi=10.1086/375637}}</ref> Subsequent investigation has refuted these claims.<ref>{{cite journal | last=Synder | first=L. | coauthors=''et al.'' | title=A Rigorous Attempt to Verify Interstellar Glycine | year=2005 | journal=Astrophysical Journal | volume=619 | issue=2 | pages=914–930 | url=http://adsabs.harvard.edu/abs/2005ApJ...619..914S | doi=10.1086/426677 }}</ref>
==== Hoaxes ====
* A separate fragment of the [[Orgueil (meteorite)|Orgueil]] meteorite (kept in a sealed glass jar since its discovery) was found in 1965 to have a seed capsule embedded in it, whilst the original glassy layer on the outside remained undisturbed. Despite great initial excitement, the seed was found to be that of a European [[Juncaceae]] or Rush plant that had been glued into the fragment and camouflaged using [[coal dust]]. The outer 'fusion layer' was in fact glue. Whilst the perpetrator of this hoax is unknown, it is thought he sought to influence the 19th century debate on [[spontaneous generation]] — rather than panspermia — by demonstrating the transformation of inorganic to biological matter.
== Objections to panspermia and exogenesis ==
* Life as we know it requires heavy elements [[carbon]], [[nitrogen]] and [[oxygen]] (C, N and O, respectively) to exist at sufficient densities and temperatures for the chemical reactions between them to occur. These conditions are not widespread in the Universe, so this limits the distribution of life as an ongoing process. First, the elements C, N and O are only created after at least one cycle of star birth/death: this is a limit to the earliest time life could have arisen. Second, densities of elements sufficient for the formation of more complex molecules necessary to life (such as amino acids) only occur in molecular dust clouds (10<sup>9</sup>–10<sup>12</sup> particles/m³), and (following their collapse) in solar systems. Third, temperatures must be lower than those in stars (elements are stripped of electrons: a [[Plasma (physics)|plasma]] state) but higher than in [[interstellar space]] (reaction rates are too low). This restricts ongoing life to planetary environments where heavy elements are present at high densities, so long as temperatures are sufficient for plausible reaction rates. Note this does not restrict dormant forms of life to these environments, so this argument only contradicts the widest interpretation of panspermia — that life is ongoing and is spread across many different environments throughout the Universe — and presupposes that any life needs those elements, which the proponents of [[Alternative biochemistry|alternative biochemistries]] do not consider certain.
* Space is a damaging environment for life, as it would be exposed to [[radiation]], [[cosmic ray]]s and [[stellar wind]]s. Studies of bacteria frozen in Antarctic [[glacier]]s have shown that DNA has a [[half-life]] of 1.1 million years under such conditions, suggesting that while life may have potentially moved around within the Solar System it is unlikely that it could have arrived from an interstellar source.<ref>{{cite web| url=http://ur.rutgers.edu/medrel/viewArticle.html?ArticleID=5898| publisher=Rutgers Office of Media Relations| title=Locked in Glaciers, Ancient Microbes May Return to Life| date=August 06, 2007| first=Ken| last=Branson}}</ref> Environments may exist within meteors or [[comet]]s that are somewhat shielded from these hazards.
* 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. However most of the heat generated when a [[meteor]] enters the Earth's atmosphere is carried away by [[ablation]] and the interiors of freshly landed [[meteorites]] are rarely heated much and are often cold. For example, a sample of hundreds of [[nematode]] worms on the [[space shuttle Columbia]] survived its crash landing from [[Mesosphere|63 km]] inside a 4 kg locker, and samples of already dead moss were not damaged. Though this is not a very good example, being protected by the man-made locker and possibly pieces of the shuttle, it lends some support to the idea that life could survive a trip through the atmosphere.<ref>[http://news.bbc.co.uk/1/hi/sci/tech/2992123.stm BBC NEWS | Science/Nature | Worms survived Columbia disaster<!-- Bot generated title -->]</ref> The existence of [[Martian meteorite]]s and [[Lunar meteorite]]s on Earth suggests that transfer of material from other planets to Earth happens regularly.
* [[Occam's Razor]] implies that when developing a hypothesis, we should avoid making evidentially unsupported presumptions about things if at all possible. See [[heuristic|heuristic arguments]]. From this perspective, geogenesis appears to be the default assumption when compared with panspermia or exogenesis. The former assumes a single step: that life originated on Earth, where it is now commonly observed, excluding the presumption that life formed elsewhere, in places where it has never been observed before. Geogenesis eliminates the unsupported presumption of life existing beyond the Earth, but requires a lot to happen in a relatively short time frame in order for life to arise. Exogenesis allows for a longer period of time than could be offered on Earth. Given that an understanding of life's emergence remains speculative, however, the perception of which presumption (life beyond Earth or life emerging rapidly) is preferable can be less than clear.
* Supporters of exogenesis also argue that on a larger scale, for life to emerge in one place in the Universe and subsequently spread to other planets would be simpler than similar life emerging separately on different planets. Thus, finding any evidence of extraterrestrial life similar to ours would lend credibility to exogenesis. However, this again assumes that the emergence of life in the entire Universe is rare enough as to limit it to one or few events or origination sites. Exogenesis still requires life to have originated from somewhere, most probably some form of geogenesis. Given the immense expanse of the entire Universe, there is a higher probability that there exists (or has existed) another Earth-like planet that has yielded life (geogenesis) than not. This explanation is more preferred under Occam's Razor than exogenesis since it theorizes that the creation of life is a matter of probability and can occur when the correct conditions are met rather than in exogenesis that assumes it is a singular event or that Earth did not meet those conditions on its own. In other words, exogenesis theorizes only one or few origins of life in the Universe, whereas geogenesis theorizes that it is a matter of probability depending on the conditions of the celestial body. Consider that even the most rare events on Earth can happen multiple times and independent of one another. However, since to date no extraterrestrial life has been confirmed, both theories still suffer from lack of information and too many unidentified variables.
== Directed panspermia ==<!-- This section is linked from [[Raëlism]] -->
A second prominent proponent of panspermia was the late Nobel prize winner Professor [[Francis Crick]], [[Order of Merit|OM]] [[Fellow of the Royal Society|FRS]], who along with [[Leslie Orgel]] proposed the theory of '''directed panspermia''' in 1973. This suggests that the seeds of life may have been purposely spread by an advanced extraterrestrial civilization. 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 civilization facing catastrophic annihilation, or hoping to [[terraforming|terraform]] planets for later colonization. Later, after biologists had proposed that an "[[RNA world]]" might be involved in the origin of life, Crick noted that he had been overly pessimistic about the chances of life originating on Earth.<ref>"[http://www.fasebj.org/cgi/reprint/7/1/238.pdf Anticipating an RNA world. Some past speculations on the origin of life: where are they today?]" by L. E. Orgel and F. H. C. Crick in ''FASEB J.'' (1993) Volume 7 pages 238-239.</ref> See: [[Francis Crick#Directed Panspermia|Francis Crick]].
Directed panspermia in reverse, from Earth to new solar systems, has been proposed to expand life in space.<ref> {{Citation | last = Mautner | first = M. N. | title = “Directed panspermia. 3. Strategies and motivation for seeding star-forming clouds” | journal = J. British Interplanetary Soc. | volume = 50 | pages = 93 | year = 1997 }} </ref>For example, microbial payloads launched by solar sails at speeds up to 0.0001 ''c'' (30,000 m/s) would reach targets at 10 to 100 light-years in 0.1 million to 1 million years. Fleets of microbial capsules can be aimed at clusters of new stars in star-forming clouds where they may land on planets, or captured by asteroids and comets and later delivered to planets. Payloads may contain extremophiles for diverse environments and cyanobacteria similar to early microorganisms. Hardy multicellular organisms (rotifer cysts) may be included to induce higher evolution.<ref> {{Cite book | last = Mautner | first = Michael Noah Ph.D.| author-link = Michael Noah Mautner | title = Seeding the Universe with Life: Securing our Cosmological Future | publisher = Legacy Books (www.amazon.com) | date = 2000 | isbn = 047600330X}} </ref>
The probability of hitting the target zone can be calculated from <math>P(target) = \frac{A(target)}{\pi (dy)^2} = \frac{a r(target)^2 v^2}{(tp)d^4}</math> where ''A''(target) is the cross-section of the target area, ''dy'' is the positional uncertainty at arrival; ''a'' - constant (depending on units), ''r''(target) is the radius of the target area; ''v'' the velocity of the probe; (tp) the targeting precision (arcsec/yr); and ''d'' the distance to the target (all units in SIU). Guided by high-resolution astrometry of 1×10<sup>−5</sup> arcsec/yr, almost nearby target stars (Alpha PsA, Beta Pictoris) can be seeded by milligrams of launched microbes; while seeding the Rho Ophiochus star-forming cloud requires hundreds of kilograms of dispersed capsules.<ref> {{Citation | last = Mautner | first = M. N. | title = “Directed panspermia. 3. Strategies and motivation for seeding star-forming clouds” | journal = J. British Interplanetary Soc. | volume = 50 | pages = 93 | year = 1997 }} </ref> The figure shows the launching of solar sail ships with effective thicknesses that will achieve final velocities as shown. The figure also shows the dispersion and capture of the microbial payload at the target solar system.
Directed panspermia is altruistic and may be motivated by life-centered “panbiotic ethics” that aims to secure and propagate our form of gene/protein organic life, and to establish life as a controlling force in nature.
Theoretically, by humans traveling to other celestial bodies such as the moon, there is a chance that they carry with them microorganisms or other organic materials ubiquitous on Earth, thus raising the curious possibility that we can seed life on other planetary bodies. The same can be said for unmanned probes manufactured on Earth. This is a concern among space researchers who try to prevent Earth contamination from distorting data, especially in regards to finding possible extraterrestrial life. Even the best sterilization techniques can not guarantee that potentially invasive biologic or organic materials will not be unintentionally carried along. So far, however, in the limited amount of space exploration conducted by humans, "terrestrial pollution" does not appear to be a problem although no concrete studies have investigated this. The harsh environments encountered throughout the rest of the solar system so far do not seem to support complex terrestrial life. However, matter exchange in form of meteor impacts has existed and will exist in the solar system even without human intervention. As evidence, some argue that anomalies found within Martian meteorite [[ALH 84001]] indicate that bacteria could travel from planet to planet without intelligent help.
Deliberate directed panspermia would seed space objects. The securing of future life would need to balance against interference with science. This interference can be minimized by targeting remote solar systems where life would not have evolved yet. Seeding a few hundred young solar systems would secure future life while leaving billions of stars pristine for exploration.
There exists speculation on a connection to the Titius-Bode Law, arguing that Earth may have received seeds of life by directed panspermia, because the extraterrestrial senders knew that Earth belonged to a solar system with stable Titius-Bode structure. See: External Link "Directed Panspermia and Titius-Bode"
== Recent Experiment ==
After enduring a 12-day orbital mission and a fiery reentry, an unmanned spacecraft, Foton-M3, awaits retrieval in a field in Kazakhstan. The 5,500-pound capsule, seven-feet in diameter, housed experiments testing the lithopanspermia theory. The capsule contained, among other things, [[lichen]] that were exposed to the radiation of space. Scientists also strapped basalt and granite disks riddled with cyanobacteria to the capsule's heat shield to see if the microorganisms could survive the brutal conditions of reentry. Alas, this batch didn't arrive alive but the scientists believe that it was at a disadvantage.
<blockquote>
"When compared to a real meteorite," says Rene Demets, the European Space Agency's coordinator for space biological experiments for this mission, "the heat penetrates quite deeply into our test samples".<ref>Popular Science February 2008 edition-Under "picture of the month" in table of contents-</ref></blockquote>
== See also ==
* [[Anthropic principle]]
* [[Astrochemistry]]
* [[Back-contamination]]
* [[Biogenesis]]
* [[Drake equation]]
* [[Fermi paradox]]
* [[Fine-tuned universe]]
* [[Forward-contamination]]
* [[Human evolution]]
* [[List of publications in biology#Origin of life|Important publications in origin of life]]
* [[List of molecules in interstellar space]]
* [[Creation myth]]
* [[Origin of life]]
* [[Paleoclimatology]]
* [[Planetary habitability]]
* [[Rare Earth hypothesis]]
* [[Red rain in Kerala]]
* [[Star Jelly]]
* [[Timeline of the Big Bang]]
* [[Universal common ancestor]]
== References ==
{{reflist}}
* Rhawn Joseph, "Astrobiology, the Origin of Life and the Death of Darwinism", University Press, 2001, ISBN 0-9700733-8-0
* Cohen, B., Swindle, T. and Kring, D. (2000) Support for the lunar cataclysm hypothesis from lunar meteorite impact melt ages. Science, 290(5497):1754 -- 1756.
* Crick F, 'Life, Its Origin and Nature', Simon and Schuster, 1981, ISBN 0-7088-2235-5
* Gilmour I, Wright I, Wright J 'Origins of Earth and Life', The Open University, 1997, ISBN 0-7492-8182-0
* FITCH FW, ANDERS E (1963) ORGANIZED ELEMENT — POSSIBLE IDENTIFICATION IN ORGUEIL METEORITE. SCIENCE 140 (357): 1097
* Hoyle F, 'The Intelligent Universe', Michael Joseph Limited, London 1983, ISBN 0-7181-2298-4
* Kring DA, Cohen BA (2002) Cataclysmic bombardment throughout the inner solar system 3.9-4.0 Ga. J GEOPHYS RES-PLANET 107 (E2): art. no. 5009
* Lepland A, van Zuilen M, Arrhenius G, Whitehouse M and Fedo C, Questioning the evidence for Earth's earliest life — Akilia revisited, Geology; January 2005; v. 33; no. 1; p. 77-79; DOI: 10.1130/G20890.1
* Louis G, Kumar AS (2006) The red rain phenomenon of Kerala and its possible extraterrestrial origin, Astrophysics and Space Science DOI: [http://dx.doi.org/10.1007/s10509-005-9025-4 10.1007/s10509-005-9025-4]
* NAGY B, CLAUS G, HENNESSY DJ (1962) ORGANIC PARTICLES EMBEDDED IN MINERALS IN ORGUEIL AND IVUNA CARBONACEOUS CHONDRITES. NATURE 193 (4821): 1129
* Narlikar JV, Lloyd D, Wickramasinghe NC, et al. (2003) Balloon experiment to detect micro-organisms in the outer space. ASTROPHYS SPACE SCI 285 (2): 555-562
* Nisbet, E. (2000) The realms of Archaean life. Nature, 405(6787):625 -- 626.
* SCHIDLOWSKI, M. (1988) A 3,800-MILLION-YEAR ISOTOPIC RECORD OF LIFE FROM CARBON IN SEDIMENTARY-ROCKS. Nature, 333(6171):313 -- 318.
* Wainwright, M. (2003) A microbiologist looks at panspermia. Astrophysics and Space Science, 285(2):563 -- 570
== External links ==
* [http://www.panspermia.org/index.htm ''Cosmic Ancestry: Life comes from space because life comes from life''], by Brig Klyce
*[http://www.sciam.com/article.cfm?chanID=sa006&colID=1&articleID=00073A97-5745-1359-94FF83414B7F0000 Did Life Come from Another World?] ''Scientific American'', November 2005.
*[http://www.panspermia.org/thirdalt.htm ''Creationism versus Darwinism: A third alternative ''], by N. Chandra Wickramasinghe & Brig Klyce
* [http://www.museumofhoaxes.com/orgueil.html The Orgueil meteorite hoax]
*[http://www.beinspace.com/dna.php ''Panspermia today ''], spread life to outer space - beinspace
* [http://www.fossilmall.com/Science/About_Stromatolite.htm About stromatolites]
* http://www.panspermia.org/ — Modern panspermia advocates. This site claims cosmic ancestry; not only that life on Earth originated in space, but that life has existed since the beginning of time, as well as an alternative explanation of evolution.
* http://www.iscid.org/brig-klyce-chat.php — cosmic ancestry
* http://www.nature.com/nsu/040216/040216-20.html
* http://www.ideacenter.org/contentmgr/showdetails.php/id/849 — Panspermia criticism from the [[intelligent design]] community
* Francis Crick's [http://profiles.nlm.nih.gov/SC/B/B/Y/P/_/scbbyp.pdf handwritten notes (PDF)] for a lecture on Directed Panspermia, dated [[5 November]] [[1976]].
* [http://www.beinspace.com/dna.php ''panspermia from Earth to other planets'',beinspace]
* http://www.tonderai.co.uk/earth/origins.php#limits
* [http://netstorage.discovery.com/science/fansites/discoveriesthisweek/video/2004/10/DTW_NasaWorms.swf Discovery Channel] — Space shuttle "Columbia" proves that atmosphere entry is possible
*[http://www.cnn.com/2006/TECH/science/06/02/red.rain/index.html Mysterious red cells might be aliens] — CNN Report by Jebediah Reed
*[http://www.althofer.de/directed-panspermia--titius-bode.html Directed Panspermia and Titius-Bode] - Speculation on a cross connection
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[[Category:Origin of life]]
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