Panspermia

The hypothesis of panspermia [ panspɛrmi ː ] ( gr πανσπερμία Panspermia, of πάν pán "everything" and σπέρμα semen "seed"; German as much as " All- seed " ) states that move simple life forms over large distances across the universe and as the beginning of life brought to earth. Their representatives hence try to respond to unmet in their opinion, the contradiction between the high complexity of life on one side and the relatively short time of its existence on the other side. Most of the scientists panspermia, however hitherto been regarded as pure speculation, since so far could only be detected on Earth life.

• 3.1 Directed Panspermia
• 3.2 Transspermie
• 3.3 Strong panspermia and Cosmic Ancestry

• 4.1 Beginning of Life
• 4.2 Critique of Panspermia hypothesis and ideological aspects

History

Progenitor of the theory of panspermia can already be seen in the ideas of the Greek philosopher Anaxagoras, who spoke of " seeds of life". These considerations came but by Aristotle's theory of spontaneous generation of life into oblivion. For that build upon medieval thought-world in Europe, the question did not arise, since the Christian doctrine of creation contradicted her. Only in the 19th century (gene aequivoca ) presented by Charles Darwin's theory of biological evolution Reason (1859 ) and Louis Pasteur's experiments on the question of spontaneous generation in 1884 for the first time many scientists clearly the problem of the origin of the first living things on Earth.

Different hypotheses about the beginning of biological evolution have been developed: in addition hylozoistischen speculation in Fechner and William Thierry Preyer here by Ernst Haeckel in 1866 first formulated views on the primeval origin of life by primary spontaneous generation, archigony or car genius was predominant. In contrast, the panspermia hypothesis similar thoughts of Jöns Jakob Berzelius (1834 ), Louis Pasteur ( 1864), Hermann Richter (1865 ), Lord Kelvin (1871 ) and Hermann von Helmholtz ( 1871) were represented. Often, but not always, it was connected to the postulate of the eternity of life; just this was also a point of criticism.

Early 20th century, Svante Arrhenius formulated with the radio - panspermia the first theoretical description of panspermia ( 1903/1908 ). According to this theory spores can escape from the outer layers of the atmosphere and are transported by the pressure of sunlight in the interstellar space ( the solar wind was at the beginning of the 20th century still unknown).

Readopted the panspermia hypotheses in 1963 by Donald Barber and in the 1970s by Francis Crick and Leslie Orgel ( directed panspermia ).

Even the British astronomer Fred Hoyle was a big advocate of panspermia hypothesis. He joined with his steady-state theory of the universe which emanates from an infinite age of the universe and thus the question of the origin of life bypasses. At least as a broad scientific consensus raised the competing Big Bang model to the prevailing cosmological theory of the dynamics of the universe, but lost his ideas attractive. Also, the fact that Hoyle made ​​its appearance as the author of several fantastic stories, increased not just the scientific reputation of his ideas that have been viewed more and more as science fiction. However Hoyles students and former employees Chandra Wickramasinghe represents active panspermistische ideas today.

1996 was finally proposed by Brig Klyce the Cosmic Ancestry version, a combination of Hoyle's panspermia hypothesis with the holistic conceptions of Gaia James Lovelock.

Arguments

A theory of panspermia has generally met with four problems:

• Life must go into the interstellar space.
• Life must survive there.
• Life does get in the capture cross section of a habitable planet.
• Life must get there intact in the biosphere.

As life comes into space?

Svante Arrhenius suggested before 1908 that microbes were transported by atmospheric processes in the outer layers, can leave the gravitational field of their planet by the light pressure of the sun or by close encounters with meteoroids. An alternative would be that material is ejected with embedded microbes in meteorite impacts into space. Electric fields could bacteria and other microbes from Earth carry into space and transport them to planets like Mars. The suspected electrical engineer Tom Dehel by the American Federal Aviation Administration, according to calculations of electromagnetic fields in the Earth's atmosphere. Until now, scientists believed that such an exchange of life is possible only by the impact of a meteorite, is hurled at the mikrobenhaltiger dust into space. Recent findings on the above options:

• Indian studies found bacteria in the stratosphere at 40 km altitude, significantly higher than previously thought.

• Simulations at the German Centre for Aerospace in Cologne showed that organisms can survive the impact that is needed to separate the rock from the parent body.

It is also speculated that life does not flourish alone on the planet: After several basic building blocks of life such as amino acids were in the late 20th century found on comets or in its coma. However, there is so far no evidence of life forms.

Survivability in space

An argument against the panspermia stating that no life forms under the conditions of outer space, that is, especially in vacuum, at temperatures close to absolute zero and the high loads caused by UV radiation and cosmic rays can survive. Even in the interior of larger bodies, where cosmic radiation is largely shielded by the radiation DNA should radioactive elements which are present in small amounts in each of naturally occurring rock, be destroyed over time.

However, there is evidence to suggest that bacteria can survive extended periods of time under these conditions:

• With the U.S. mission to the moon Surveyor 3 were placed on the moon accidentally bacteria of the genus Streptococcus withus. After their return transport to the earth, a large portion of the spores 31 months later, it was able to resume a normal life cycle.

• The BIOPAN experiments of the Institute of Aviation and Space Medicine of the German Center for Aerospace in Cologne investigate the resistance under defined conditions. On the Russian Foton satellite container have been associated with the bacterial species Bacillus subtilis into orbit and opened there for two weeks. After returning to Earth, several thousand of the starting population had survived the time in orbit without any cover or protector. Further experiments showed that living organisms, which are covered by the UV radiation, for example, by a dust layer, can survive for several years in space. You could also survive several million years but may, if they are shielded in a several meters large body of rock by cosmic rays.

• There is a particular group of organisms that are able to survive even in very inhospitable places It cyanobacteria of the genus Chroococcidiopsis and in particular to the extremophile bacterium Deinococcus radiodurans, which is only slightly sensitive to ionizing radiation; it was found in plants, intended to make the food preserved by irradiation.

• The bacterium Desulforudis audaxviator lives alone in groundwater few kilometers deep in the rock and can obtain its energy solely from hydrogen peroxide and hydrogen, which are formed at this depth only by natural radioactivity in the rock. Under these conditions, cell division would require a time in the order of 100 to 1,000 years.

• Some multicellular organisms, such as water bears, are able to cryptobiosis. This allows some of them to survive space conditions.

Caught in the capture cross section of a habitable planet

Is life fall into interstellar space, it is hundreds of thousands of years on the road, at best, up to the next habitable planet.

Survivability on impact

After its passage, the cosmic life forms to survive their way through the earth's atmosphere on the planet's surface, which is associated with exposure to strong deceleration forces and great heat. Meteoroids which penetrate the Earth's atmosphere and reach the earth's surface as meteorites are heated only at the surface and melted. As early as one centimeter depth the material is hardly heated, so that the survival of microorganisms seems possible. Meteoroids are decelerated in the atmosphere below a certain size at free fall speed, so that the impact energy is not sufficient to rule out a survival. The amount of Martian matter that was heated in the past four billion years ago on the way to earth does not exceed 100 ° C, is approximately four billion tons.

Extreme habitats on Earth

In the late 20th century, has found life forms under very " hostile " conditions on the ground, among which one hätte.Extremophile not thought possible life before There are now many bacterial strains are known that are not dependent on the sun as an energy source, but other use chemical processes, for example in volcanoes, the hot springs in the deep sea vents ( black smokers ) and underground lakes. So now lives deep in the Antarctic ice cores has been at temperatures greater than 120 ° C, in highly acidic environments or in more than 1,000 meters found ( see Vostok ). These findings confirm the assumption that life is far more resilient than was thought it was decades ago.

Cosmic evidence

After the discovery of ever more complex molecules in interstellar clouds, the simplest amino acid glycine could be detected in 2002. In 1969 fallen, very primitive meteorite Murchison amino acids, diamino acids and other organic compounds were found.

Characteristics of the found in the Antarctic meteorite ALH 84001 Martian be interpreted by some researchers as even traces of fossil bacteria - an interpretation which, however, is highly controversial.

Variants of panspermia

Directed panspermia

Another prominent protagonist of panspermia, the Nobel laureate Francis Crick, formulated in 1973, along with Leslie Orgel theory of directed panspermia. According to this theory, the spores of life are not accidental fall into space, but has been intentionally sent by an extraterrestrial civilization. The sending of small grains with bacteria Crick is the cheapest and most effective way to convey life to a potentially viable planet. The reason is, for example, considered that the civilization of the inevitable downfall looked forward to or hoping for a terraforming other planets for later colonization.

Transspermie

In the late 1990s and at the beginning of the 21st century, some consideration has been given to investigate the transport is not between planetary systems, but only between neighboring planets. This process is called Transspermie (English transpermia ). This form of panspermia is considered speculative, but as a way much more be considered as the aforementioned panspermia in a broader sense.

After the already mentioned work of researchers at Mileikowsky arrived in Earth more than four billion tons of Martian material to Earth, which was not more than 100 ° C heated in this process. Also the opposite way from the Earth to Mars took a while smaller, but still significant amount of material. If life on Mars are found, it could therefore be possible that a close relationship exists with earthen life. The question would then, however, where life originated on Earth or on Mars.

Strong panspermia and Cosmic Ancestry

The proposed by Fred Hoyle, also referred to as strong panspermia version takes as opposed to " weak" panspermia that not only the simplest life from outer space came to earth, from which then according to the theory of evolution, biodiversity and specifically the genetic structure of modern organisms newly developed, but assumes that this diversity already in " genetic programs " was created from the universe coming germs of life. In particular, the strong panspermia rejects macroevolution and microevolution accepted only as a fine adjustment to the environment. Life has always been part of would thus be an infinitely old universe.

The propagated as Cosmic Ancestry version extends the strong panspermia, by involving hypotheses from the Gaia environment under which the biosphere, the environmental conditions of a planet actively controlled to produce the most favorable conditions for life.

Classification of the theory of panspermia

At the beginning of the 21st century, few people are working systematically on the theory of panspermia, even if it is considered by many scholars and institutions such as the U.S. space organization NASA and the German Aerospace Center (DLR ) is not rejected in principle. In particular, the Transspermie hypothesis in relation to Earth and Mars will be drawn at least as a possibility.

Beginning of Life

The main motivation for panspermia is the fact that life has left detectable traces very early on Earth.

The oldest known minerals of the earth's crust are about 4.4 billion years old zircons, suggesting a first cooling of the young Earth. However, existing at the time the crust was completely destroyed probably by the impact of many asteroids and comets and other geological processes. The world's oldest rocks, dating to almost four billion years, could form a partially preserved until today solid crust until about 3.8 billion years ago, after about 3.9 billion years ago, the frequency of meteorite impact had waned considerably, as confirmed by studies of lunar craters. Usually, the chemical evolution is from the simplest molecules via complex biomolecules to entire organisms considered unlikely before that date.

The oldest fossils may be from 3.54 to 3.56 billions of years old stromatolites, which were found in Australia and South Africa; geochemical isotope analyzes even already show abnormalities in the oldest rocks, which also point to life. These datings are, however, currently being discussed again, as there is evidence that organisms may be penetrated from later geological epochs in the older rocks, or that the geochemical anomalies could also purely inorganic causes. Should confirm the initial dating, life on earth seems almost immediately with the presence of the first liquid water or the first oceans to have existed (oxygen isotope analyzes in the oldest zircons are, however, interpreted by some scientists that already for their crystallization ago 4 could have 4 billion years, both continental crust and oceans on the Earth's surface exists).

A possible explanation of this almost " earliest possible " proof of life is that its origin is an almost self-evident process in the universe that takes place almost abruptly, as soon as permitted by the environmental conditions.

Supporters of the panspermia hypothesis have in turn suggests that the spontaneous generation could necessarily only include chemical and physical processes. However, precisely the formation of long-chain molecules indispensable and the pronounced predominance of chirality at the living beings on the earth is not explainable within the allotted time scale by a currently known chemical or physical interaction. Although there exist mechanisms that can separate the living beings of different chirality, but it remains unclear how environmental conditions may favor one chirality.

In addition, there was no evidence that the formation of living organisms in favorable conditions automatically takes place; On the contrary, it is still not possible to produce life-like structures under arbitrary conditions ( laboratory experiments). Representatives of the panspermia hypothesis also point to the discrepancy that decrease from unicellular to multicellular organisms, the time steps for the development of more complex forms of life continues; during the development of cyanobacteria has taken to other unicellular about a billion years to have taken place within a hundred million years ago the spontaneous generation.

In the panspermia stood considerably more time and by a transfer through space an infinite number of planets for the formation of life available. A simple calculation follows that each point of the Milky Way was reached within 20-50 million years ago, even at relatively low cosmic speeds. The detection of life on planets outside the solar system with spectral analysis is not possible because of the much too weak reflection of the planet. An alleged special status of the earth so was unfounded.

The panspermia explains not aware of the origin of life itself, which is transferred to other places and times, or even has never taken place according to some of their representatives. In the latter case it is assumed that the universe does not have a finite age, is life next to space, time and matter with the fundamental constituents of the universe. This notion is, however, in contrast to the now generally accepted Big Bang model, according to which the universe is about 13.7 billion years old. The followers of this panspermia variant are thus forced to resort to alternative models of the cosmos as the steady-state model.

Less extreme is the idea that life originated in a different place in the universe, from where it has spread in the universe and was finally arrives on Earth. She has over the aforementioned variant has the advantage not to be in contradiction with established cosmological theories, but provides the view of its supporters still significant advantages over the prevailing opinion that the first life forms would have formed on Earth since at least potentially much more standing time for the origin of life are available.

Critique of Panspermia hypothesis and ideological aspects

The advocates of panspermia have a diverse background that ranges from reputable scientists, although they consider the panspermia as very speculative but quite scientifically treatable on interested laypeople to more pseudo-scientific working or religiously influenced representatives. From science, particularly of evolutionary biologists, often comes the objection that many versions of panspermia are unscientific because they are difficult or not scientifically verifiable. The radical notion particular, life has always existed, is considered by the majority of today predominant Big Bang model of cosmology with the consequent finite age of the universe be refuted.

But even the less radical ideas are criticized, because the only ways of verifying argues, is to send probes to other planets and found in meteorites or comets unique and extraterrestrial life traces. This is to be expected either extremely complex or very low probability. In contrast, the panspermia is difficult falsifiable because there is little information about the conditions on Earth at the time of the origin of life. Just Creationism shows that proponents apparently lined up in scientific successes in overcoming difficult obstacles more hurdles. This always remains a back door open.

The discovery of organic material in meteorites, comets or anywhere else in the universe does not change the dubious position of panspermia, since the emergence of organic material on earth, with its diverse chemistry should have been the first legally possible. This has been demonstrated by various experiments, including the now famous Urey -Miller experiment. Hence the so-called pseudo - panspermia is true, that is the view that no simple life, but only the basic building blocks of life ( organic compounds ) from the universe originate, for the explanation of the origin of life on earth not as necessary.

In organized form the panspermia is present, for example, represented by the Interstellar Panspermia Society. This organization has officially taken on the task of promoting scientific research specifically for directed panspermia and to facilitate their implementation. At the same time this organization spreads a designated " Astrobioethic " ethics catalog. The latter is often interpreted to mean that there is yet QUESTION IS more than just an association that seeks to promote exceptional projects, but also an ideological association - Panspermia opponents practice because of the religious features of strong criticism of this organization. In addition, has the influence of the Gaia hypothesis within the Cosmic Ancestry panspermia suggests that panspermia - world images can accept because of their fascination sectarian features, roughly comparable to Scientology or the Raelism.

Although with Lord Kelvin, the first of the panspermia represented a antidarwinistischen position, which also had religious motivations that panspermia by creationists is currently generally rejected as another naturalistic worldview alongside the theory of evolution. Panspermia representatives consider the panspermia usually as the third way between evolutionary theory and creationism. Nevertheless, there are also points of contact, such as the rejection of the modern theory of evolution, especially of macroevolution, sheen using scientific arguments. So used about Brig Klyce, a representative of the "Cosmic Ancestry " mentioned form of panspermia, originally derived from the concept of creationism " irreducible complexity " to argue against the theory of evolution. It is also conceivable that some versions of panspermia, as just the " Cosmic Ancestry " version that can be adapted in a modified form by creationists.

With the exception of some prominent scientists like Francis Crick and Fred Hoyle, the panspermia currently only plays a marginal role in science in its general form. Only in the form of Transspermie it is quite reputable pulled in planetology and astrobiology into consideration. If on one of the planets or moons in the solar system life forms are found, which have similarities to earthly life that can not be explained by chance alone or convergent evolution beyond Earth, the Transspermie, however, would gain new relevance.

Science Fiction

The idea of ​​panspermia was taken up in a series of science fiction novels, particularly worthy of mention here Jack Finney repeatedly filmed novel are the Body Snatchers and the Dragon Rider books by Anne McCaffrey and the Quest Books and The carpet maker by Andreas Eschbach.

Often the panspermia is also used as fictional explanation for the most humanoid aliens and their most Earth-like home planet. For example, in the Star Trek series where Urhumanoide called aliens deliberately provoke the evolution of intelligent species on the basis of their own genetic material.

The PC game Spore, in which it mainly comes to their own biological systems through evolution to "create", begins by selecting a planet, always with the incidence of microorganisms from outside.