Abiogenesis

As chemical evolution is called a hypothesis for the formation of organic molecules from inorganic molecules ( abiogenesis ) in the Hadean between the formation of the Earth around 4.6 billion years and the origin of life, the beginning of biological evolution, in about 4.2 to 3, 8 billion years ago.

From abiotically - inorganic molecules is accordingly formed under the influence of energy initially organic compounds and prebiotic molecules from which emerged later, first living creature. Similar processes may also wherever possible in the universe where moderate temperature zones exist (eg on Planemos / Exoplanets ). The generation of organic materials, ie, carbon-hydrogen compounds is considered a prerequisite for the development of living organisms, as well as, for example, the presence of moderate temperatures, the absence of high-energy electromagnetic radiation and the presence of water as solvent medium and ( cosmochemistry ).

The reconstruction of this evolution is difficult because fossils and accurate knowledge of the geochemical conditions of the Earth some 3.8 billion years missing.

Therefore, there are various hypotheses on the progress of the chemical evolution. They are mainly supported by experiments that are based on assumptions about the former chemical composition of the Earth's atmosphere, hydrosphere and lithosphere as well as climatic conditions. On the origins of the hydrosphere Article origin of terrestrial water goes a closer.

The experiments which support the hypotheses rich, currently not sufficient to formulate a theory that can explain how life originated. Thus, although could already be observed the emergence of complex chemical molecules that are essential for biological processes, but no education nor a sufficient system of it. These observations are counted but already a great success and sufficient for the formation of the hypothesis.

With all the uncertainty about the actual origin of life on Earth seems to be sure that only one form of life, namely to nucleic acids (RNA and DNA) based, has set (if it should ever have been more different ). The main sign of this theory is the equality of the two most important building blocks of life typically macromolecules ( proteins and nucleic acids ), the five nucleotides and 20 amino acids in all known forms of life, but also in particular the universal genetic code valid.

It is also believed that the emergence of new life on earth is no longer possible now that all ecosystems are already occupied by life and the emergence of new life under the competitive pressure from other living beings is very unlikely.

3.1 The Miller - Urey experiment
3.2 Other reactions
3.3 Participation of minerals and rocks
3.4 The iron-sulfur world ( ESW ) after Wächtershäuser
3.5 The formation of macromolecules
3.6 Education prebiotic structures ( cell precursors ) 3.6.1 coacervates
3.6.2 microspheres
3.6.3 protocells

4.1 biomolecules from space
4.2 Black Smoker

Survey

Hypotheses on the chemical evolution must explain several aspects:

Posts to come, among others, the following scientists:

Alexander Oparin: coacervates (see below)
Harold C. Urey and Stanley L. Miller 1953: emergence of simple biomolecules in a simulated primitive atmosphere (see below)
Sidney W. Fox: microspheres of Protenoiden (see below)
Thomas R. Cech (University of Colorado) and Sidney Altman ( Yale University, New Haven, Connecticut ) 1981: autocatalytic RNA splicing: " ribozymes " unite catalysis and information in one molecule. They are able to cut out from a longer RNA chain itself and join the remaining ends again.
Walter Gilbert ( Harvard University, Cambridge ) developed the idea of the RNA world 1986 (see below)
Günter von Kiedrowski (Ruhr - University Bochum) published in 1986 the first self-replicating system based on a hexanucleotide (DNA), important contributions to the understanding of the growth functions of self-replicating systems.
Manfred Eigen (Max- Planck - Institute for Biophysical Chemistry Göttingen ): Evolution of RNA-protein ensembles. Hypercycle.
Julius Rebek, Jr. (MIT Cambridge ) provides an artificial molecule ago ( Aminoadenosintriazidester ), which replicates in chloroform solution itself. However, the copies are identical with the template, so that an evolution of these molecules is not possible.
John B. Corliss ( Goddard Space Flight Center, NASA): Hydrothermal vents of the seas provide energy and chemicals that allow one of meteorite impacts largely undisturbed chemical evolution. Today they are habitat for many features very primitive archaebacteria ( Archaea).
Günter Wächtershäuser (München ): The first self-replicating structures with metabolism were created on the surface of pyrite. The iron sulfide of the pyrite has supplied thereto the energy required. With the growing and decaying back pyrite crystals, these systems would grow and multiply, and the different populations were exposed to different environmental conditions ( selection criteria ).
AG Cairns -Smith (University of Glasgow ) and David C. Mauerzall (Rockefeller University, New York) in clay minerals see a system that is first subjected to chemical evolution itself, which many different, self-replicating crystals are formed. These crystals draw due to their electric charge to organic molecules and catalyze the synthesis of complex molecules, wherein the information content of the crystal structures initially serves as a template. These organic structures are more complex, until they can reproduce without the help of the clay minerals.
Wolfgang Weigand, Mark Dörr et al. ( Friedrich -Schiller- University Jena) 2003 show that iron sulfide can catalyze the synthesis of ammonia from molecular nitrogen.

Still available from a single model for chemical evolution, possibly because basic principles were not yet discovered.

Preliminary

Biomolecules

The prebiotic formation of complex organic molecules can be divided into three steps:

The elemental analysis of these molecules leads to the question of which inorganic compounds to their formation were necessary.

All hypotheses assume that in addition to water and phosphate initially were available only the reduced forms of the present-day chemical compounds in sufficient quantity as the primordial atmosphere contained hardly any molecular oxygen.

As a source of energy UV rays, heat of volcanic processes, ionizing radiation emitted by radioactive processes and electrical discharges are accepted. After some very notable recent theories the energy required would alternatively for the formation of organic molecules to and from anaerobic redox processes between reduced volcanic gases and sulfide minerals such as pyrite ( FeS2 ).

The role of water for the evolution of life

Life as we know it (or define ), requires water as a universal solvent. It has properties that has been accepted by natural scientific understanding enable the emergence of life (see also Anthropic principle). Maybe life can arise and exist independently of water, but many scientists believe that the presence of liquid water ( in a particular area or on a particular planet, such as Mars ) makes our way of life, not only, but its rise even very likely makes.

For the origin of life following properties of water are relevant:

Water is liquid in a temperature range in which organic molecules are stable.
Water is particularly useful because it allows a homogeneous mixture, can provide protons for catalysis available and has a high heat capacity and thus absorbs excess heat of reaction as a polar medium for chemical reactions.
Water has globally small fluctuations in temperature and osmotic values on ( locally can make big differences arise ), which leads to a globally balanced climate.
Water absorbs the harmful UV radiation to macromolecules. These penetrates frozen water (ice) up to a certain depth.
Water, are dissolved in the materials, such as sea water, forms on freezing regions of different concentrations, which are surrounded by Eismembranen ( sea-ice hypothesis). This compartmentalization and the resultant concentration gradient is regarded as necessary for the formation of biologically active molecules.
The anomaly of water prevents water ice from the ground up, and provides a region of uniform temperature.

Development of the earth's atmosphere

The development of earth's atmosphere is a part of the chemical evolution and also an important element of climate history. It is now divided into four main stages:

Primordial atmosphere

At the beginning of the formation of chemical elements in the universe (described in cosmochemistry ) and the formation of the Earth from these were - was created around 4.56 billion years ago. The earth already possessed very early on a presumably of hydrogen (H2) and helium ( He) existing gas envelope, but again lost. Astronomers go beyond that even assuming that initially in the formation of the solar system on Earth and all the other near the sun planet because of the relatively high temperatures and the effects of the solar wind with little or no light elements (including carbon, nitrogen and oxygen), " left " have remained. All of these elements that today make up the majority of the biosphere would have been only after a considerable time delivered according to this theory by comets from the outer regions of the solar system, after the proto-planet had cooled somewhat. Since constantly repeated large impact events of celestial bodies during the first few hundred million years after the solar system formed, were living systems that are already developed in these times, been repeatedly destroyed by global sterilizations, which were caused by large collisions. The development of life could start so only after liquid water could hold at least at the lowest points of the earth's crust in the consequent forming seas in the long run.

First atmosphere

The slow cooling of the Earth, volcanism occurring ( outgassing from the earth ) and the global distribution of matter is proposed comet it came to the establishment of an atmosphere. Therein as compounds mainly water vapor (H 2 O, up to 80%), carbon dioxide ( CO2, up to 20% ), hydrogen sulfide (H2S ), ammonia (NH3) and methane (CH4) as the main components to be expected. It is precisely those products of volcanism or the comets that we can still be seen today. The high percentage of water vapor due to the fact that the earth's surface was too warm at this time to form large seas. The water evaporated for the most part once again, though it must have rained constantly over millions of years. However, the actual origin of the water is still partially controversial. Can, especially from water, methane and ammonia under the conditions of the early Earth first small organic molecules ( carboxylic acids, alcohols, amino acids), and later Tholins (such as on Saturn 's moon Titan ) and organic polymers (polysaccharides, fats, polypeptide ) form, which are not stable in the oxidizing atmosphere.

Second atmosphere

After the temperature of the atmosphere had fallen below the boiling point of water, there was an extremely long duration of rain, so that the oceans were formed. Accordingly, the other atmospheric gases were enriched relative to water vapor. The high UV - radiation -induced photochemical decomposition of water, methane and ammonia molecules, resulting in carbon dioxide and nitrogen accumulated. The light gases such as hydrogen or helium faded away for the most part into space, carbon dioxide dissolved in large quantities in the oceans, so their water was acidified and the pH thereof to absenkte to about 4. The inert and sparingly soluble nitrogen N2 remained unchanged, collected at the time and formed about 3.4 billion years ago the main constituent of the atmosphere.

The precipitation of the carbon dioxide with metal ions as carbonates and the later development of living organisms, the carbon dioxide assimilated, led to a reduction in CO2 concentration and a re - increase of the pH values of the waters.

Third party atmosphere

The oxygen (O2) plays the leading role in the further development towards today's atmosphere. It was formed by the appearance of organisms with oxygener photosynthesis, namely since possibly about 3.5 billion years ago; presumably there were forerunners of today's cyanobacteria or cyanobacterial -like prokaryote. Although the CO2 assimilation led to a further decrease of the concentration of carbon dioxide, however, the oxygen concentration of the atmosphere was low. The reason for this is that O2 was used immediately for the oxidation of divalent iron ions and other easily oxidizable substances in the oceans and only slowly accumulated in the atmosphere after these compounds were almost completely oxidized before about two billion years ago.

The highly reactive oxygen reacts readily with some sensitive organic biomolecules. Therefore, the increased occurrence of oxygen two billion years ago introduced for the early organisms a tremendous be selected environmental factor represents only a few of the former probably obligate anaerobic organisms could retreat in oxygen-free habitats, another part apparently evolved enzymes, the toxic peroxides or other oxygen - metabolites render harmless (for example, superoxide dismutases, peroxidases and catalases ). Finally, developed in some microorganisms, with the participation of such enzymes as precursor forms even the most complex membrane enzymes, which utilize the oxygen present metabolically to produce energy for the growth of their own cells: the Endoxidasen the aerobic respiratory chain. Depending on the organism, there are several different forms of Endoxidasen as quinol oxidases or cytochrome c oxidase, each also varies with copper ions and hemins containing active centers are equipped and therefore most likely derived from several parallel lines of development. In many cases, even more Endoxidase types are next to each other to find the same organism and are synthesized depending on the prevailing environmental conditions. These enzymes represent the last link of several sequentially connected enzyme complexes, the " cache " the energy from redox initially by translocation of protons or Na ions in the form of membrane potential. The membrane potential is finally again converted to chemical energy in the form of ATP via another enzyme complex, ATP synthase. The ATP synthase and the other components of the respiratory chain must be evolutionarily much older than the Endoxidasen because they (or very similar paralogous systems ) in many obligate anaerobic metabolic processes ( anaerobic respiration, methanogenesis and many fermentation pathways) and also in the anoxygenic and oxygenic photosynthesis already important roles.

A billion years, the oxygen concentration also exceeded the target of one per cent, which could form a first ozone layer a few hundred million years later. Today's oxygen content of nearly 21 % was finally achieved 350 million years ago and has since remained fairly stable.

Experiments and hypotheses of chemical evolution

The Miller - Urey experiment

The Miller - Urey experiment is based on one of the most well-known hypotheses about the evolution. It was published in the twenties of the 20th century by the Russian AI Oparin and British researchers JBS Haldane. The theory is that the conditions of the earth at that time favored certain chemical reactions. From simpler compounds of the atmosphere and of the sea to have been synthesized organic compounds. The necessary energy is supplied by the very intense UV radiation that could penetrate through lack of O2 and O3 in the atmosphere unimpeded.

1953 was reviewed by chemist Stanley Miller and Harold C. Urey of by the primordial soup experiment this hypothesis. In the experiment, they showed that in a - the assumed prebiotic conditions similar - environment, by supplying energy ( lightning ), inorganic compounds ( water, ammonia and hydrogen) and methane occur more complex organic compounds such as amino acids and lower carboxylic acids and fatty acids can. Later, most complicated built Ursuppenversuchen both all the essential building blocks of living organisms ( amino acids, lipids, purines ( nucleotide bases ) and sugar), as well as the complicated organic compounds porphyrins and Isoprene could be produced.

Although this was shown the fundamental possibility of the natural formation of organic molecules, the importance of this result for the actual flow of the emergence of life on earth is seen often criticized today. In the primordial soup experiment was then assumed that the Earth's atmosphere was chemically reducing character of what the then state of knowledge corresponded. Today, however, often assumed to be only weakly reducing or even neutral atmosphere at this time, however, the question is not yet fully understood and there are also discussed local chemical inhomogeneities of the atmospheric conditions, such as in the vicinity of volcanoes. Although it has been shown by subsequent experiments that even under such altered atmospheric conditions, organic molecules are formed; even those that have not occurred in the original experiment, but the yield is greatly reduced. That is why it is often argued that other possibilities of origin of organic molecules must have at least played an additional role. Cited here are mostly the formation of organic molecules in space and their transfer to Earth by meteorites or the development in the area of so-called black smokers.

As a further argument against the origin of the biological molecules in accordance with the organic Ursuppenversuch is often stated that in this test, a racemate, i.e. a mixture of L-amino acids and D-amino acids was. However, all occurring in living organisms, amino acids are purely the L configuration (see Biological chirality ). It would have to be a natural process, the chiral molecules of certain handedness selects preferred. From exobiologist should be noted that this is easier to explain in the universe, because photochemical processes, are with circularly polarized radiation, as produced for example by pulsars able to destroy only certain chiral molecules handedness. Actually chiral organic molecules have been found in meteorites in which the frequency of the L-shape up to 9 % predominated. However, it was shown in 2001 that also self-replicating peptide systems are able to strengthen effective homochiral products from a racemic original, which supports these researchers believe the view of earthly origin of the handedness of biological molecules.

Further reactions

From occurring during the Miller - Urey experiment intermediates formaldehyde ( CH2O) and hydrogen cyanide (HCN ) can be prepared more biomolecules under the simulated conditions of the Earth 4.5 billion years ago. Thus succeeded Juan Oro 1961, the synthesis of adenine:

He also demonstrated the formation of adenine and guanine by thermal polymerization of ammonium cyanide in aqueous solution. From ribose, adenine triphosphate and creates the adenosine triphosphate ( ATP), which in the organisms as a universal energy carrier and as a building block (as monophosphate ) of ribonucleic acids ( RNA) is utilized.

Composed of minerals and rocks

Of rocks in tiny cavities, the organic molecules are protected against UV radiation.
Crystal surfaces can serve as a matrix for growing macromolecules. The crystal surfaces may prefer certain types of molecules. L-and D -amino acids are attached to a calcite crystal at different locations.
Aharon Katchalssky ( Weizmann Institute Israel) could produce proteins with a chain length of more than 50 amino acids in almost 100 percent yield in aqueous solution with the help of the clay mineral montmorillonite.
Metal ion may act as catalysts or as electron donors, or be incorporated into biomolecules.
Clay minerals often have an electrical charge and can attract and hold as charged organic molecules.

The iron-sulfur world ( ESW ) after Wächtershäuser

A particularly intense form of participation of minerals and rocks in the prebiotic synthesis of organic molecules may have occurred on the surface of iron sulfide minerals. The theory of Miller Urey namely has serious limitations on, particularly in view of the absence of a declaration for the polymerization of the monomeric building blocks formed of the biomolecules.

An alternative scenario for the early evolution of life has therefore been developed since the early 1980s by the Munich patent law Günter Wächtershäuser who could quickly gain the support of the philosopher Karl Popper for his alternative theory. After that, life on earth to the surface of iron -sulfur minerals would have arisen, ie sulfides, which still formed through geological processes at deep-sea volcanoes that occurred on early Earth still much more common and probably on many exoplanets and Planemos must be present. The great advantage of this approach over other theories is that it has the potential, for the first time to link the formation of complex organic molecules on a continuously available and reliable energy supply. The energy comes from the reduction of iron in iron-sulfur minerals such as pyrite ( FeS2 ) with elemental hydrogen ( H2) into being ( reaction scheme: FeS2 H2 ⇌ FeS H2S) and provides enough energy to power a prebiotic synthesis of ammonia and also to endergonic to drive synthetic reactions of monomeric building blocks of biomolecules and their polymerization. Similar to ferrous ions also form other heavy metal ions with hydrogen sulfide insoluble sulfides (see sulfide group).

In addition, pyrite and other iron-sulfur minerals have positively charged surfaces where the predominantly negatively charged biomolecules (organic acids, phosphate esters, thiolates ) attach (often by complex formation reactions) concentrate, and can react with each other. For this purpose, necessary substances such as hydrogen sulphide, carbon monoxide and ferrous salts come out of solution also directly on the surface of this " iron-sulfur world" ( ESW ). Wächtershäuser draws for his theory that still existing mechanisms of the metabolism approach and derives from this an internally consistent scenario of the synthesis of complex organic molecules and biomolecules (organic acids, amino acids, sugars, nucleic bases, lipids) from simple inorganic precursor molecules found in volcanic gases are (NH3, H2, CO, CO2, CH4, H2S).

In contrast to the Miller Urey hypothesis, no force is needed from the outside in the form of flashes, or UV radiation; Moreover, the first simple chemical reactions proceed at elevated temperature much faster, without being thereby (such as enzyme- catalyzed biochemical reactions ) disabled. Since be achieved at deep-sea volcanoes temperatures up to 350 ° C, one can imagine the origin of life at these high temperatures well. Only later, after the emergence of temperature-sensitive catalysts (vitamins, proteins), the further evolution must have taken place in cooler niches.

The Wächtershäuser scenario therefore fits well with the observed ratios in the deep sea black smokers because in these structures such ecological niches appear by steep temperature gradients from the inside out easily possible. Also, the present living microorganisms, which are regarded as the primitive, at the same time with a thermophilsten ( previous ) maximum temperature for growth at 113 ° C. In addition, iron-sulfur centers have an important function in many enzymes such as current the respiratory chain. This may indicate that the initial participation of Fe-S minerals in the evolution of life, especially as this also today still represent metabolic products of anaerobic bacteria.

The formation of macromolecules

Biomacromolecules are proteins and nucleic acids. The extension of molecular chains ( polymerization) requires energy and takes place with elimination of water (condensation reaction). Conversely, the cleavage of the macromolecules (hydrolysis) provides energy. As far as the chemical equilibrium is on the side of the monomers, that these reactions are thermodynamically irreversible in the direction of polymer hydrolysis, there can be no polymer synthesis without added switched energy -providing system. Also by theoretical auxiliary constructs as evaporation of water, adding salt ( removes water) or precipitation of the products, this problem is almost unaffected. The formation of life is therefore most likely linked to the coupling of a reliable energy source which can be used for the polymer synthesis.

But

The energy source is now used in biochemistry, especially ATP, the formation of which, however, already presupposes the presence of enzymes. Under the terms of the proto- Earth you can imagine on the other hand, the energizing of the polymer synthesis by hydrolysis of polyphosphate, which is still used today by some enzymes instead of ATP. However, it is difficult to imagine even with polyphosphates that this stood in the necessary quantities available, because they can be formed spontaneously, although when phosphate-containing solutions are evaporated, but also hydrolyze relatively quickly again spontaneously when they come back into solution. From these considerations, one would have as origin of life demand a shallow sea bay, which dries out regularly and is flooded again. However, this also all water-dependent processes would repeatedly interrupted and the origin of life at least greatly delayed. Finally, however, one can also imagine a very different system in which both the synthesis of the building blocks as well as the energy-dependent formation of polymers as a continuous process taking place in an unbroken connection to a reliable energy source, namely anaerobic redox reactions with metal sulfides. These are also today released by volcanic activity still in large quantities at the bottom of the oceans, where they form including structures such as the black smoke that are densely populated by various microorganisms and higher animals.

The balance of the polymer synthesis is shifted by increasing the concentration of the building blocks (monomers ), and by dehydration of the products in favor of the formation of the polymers. This implies a compartmentalization, that is the definition of reaction chambers from each other, which are only to a limited mass transfer to the environment. In the conventional theory, this in shallow, small bodies of water ( ponds ) was settled with a high evaporation rate, which still returns as a basic idea on Charles Darwin. However, the deep sea in the major structures of black smokers are still in volcanic areas observed precipitated metal sulfides in the form of small caverns that there is an attractive scenario of an environment where all the reactions of the monomer synthesis on the concentration and polymerization of the monomers with a " built-in " can run energy conservation system.

Other solutions have been considered, but all have serious limitations and are not to bring well with the conditions on the early Earth in harmony. In most cases, is required for multiple steps or a water exclusion, which is in the chemistry laboratory easy to reach, but heavier on the proto- Earth. One of these systems is the polymerization of carbodiimides ( R -N = C = N -R) or cyanogen (N ≡ C -C ≡ N ) in anhydrous medium. Here, the condensation of the components is coupled to the reaction of the carbodiimide, the necessary energy is generated:

( HX OH = monomer, for example, amino acid or ribose)

(when R = H arises here urea)

Although cyanogen forms under UV exposure of hydrogen cyanide in desiccating pools but also the volatile molecule would be lost.

If a dry mixture of amino acids heated at 130 ° C for several hours, protein-like macromolecules form. Are polyphosphates present, satisfy 60 ° C. These conditions can result if water comes with dissolved amino acids in contact with hot volcanic ash.

A nucleotide mixture is heated in the presence of polyphosphate at 55 ° C, though polynucleotides arise, but the link is more on the 5'- and 2'- C- atoms of the ribose instead of, as they are easier than that in which is present in all organisms 5 ' -3'- linkage. For both types of polynucleotides to double helices (see Construction of DNA ) form. However, the 5'-3 ' double helix is more stable than the 5' -2'- helix.

Lack the 2'- carbon atom of the ribose, the hydroxy group, the deoxyribose exists. Now only 5'-3 ' linkages can form, as it is typical for DNA.

Formation of prebiotic structures ( cell precursors )

Cells maintain their function upright in that they form a plurality of reaction chambers ( compartments ), in which the metabolic processes take place separately and adverse reaction can be avoided; simultaneously as concentration gradients are established. There are several hypotheses was derived by means of which that such structures could emerge even before the emergence of cells.

Coacervates

Especially Aleksandr Ivanovich Oparin (1894-1980) dealt with the possibility of metabolism in coacervates (from the Latin coacervatio: accumulation ). He could show that enclosed spaces with a simple metabolism may be caused by self-organization principle, provided that catalysts are available with specific properties. Because the substances used are taken from the repertoire of the organisms living today, Oparin's coacervates are not seen as a precursor of cells, but as analogy models for the origin of precursor cells.

Is added to the colloidal solutions of biomacromolecules added salt, to form small droplets having a diameter between 1 and 500 microns, which comprise the polymers in high concentration.

Oparin examined mixtures of proteins ( histone and albumin), proteins and carbohydrates ( histone and gum arabic ) and proteins and polynucleotides ( or clupeine histone and DNA or RNA).

Include droplets of histone and gum arabic, the enzyme phosphorylase, these droplets can absorb glucose -1-phosphate from the environment, convert to starch and store. The liberated phosphate diffuses outward. The droplet becomes larger by the increase in thickness until it breaks up into smaller droplets, which may contain phosphorylase again, but less than the original droplets. Thus, also slows down the metabolism. It is clear here that led to the maintenance of the properties of a cell regeneration of the enzyme equipment is needed after graduation.

If also the starch degrading enzyme amylase added to coacervates result with a two-step metabolism:

Microspheres

In 1970 Sydney Fox was able to prove that from the proteinaceous products that occur when heating dry mixtures of amino acids (see above), can result in growing droplets by self-aggregation, called microspheres. They differ from the environment by a semipermeable membrane and take another proteinaceous material from the environment. Thus they continue to grow and divide again into smaller droplets. Furthermore, Fox found that these systems have enzymatic properties that degrade glucose or as esterases or peroxidases act without enzymes had been added from outside.

Protocells

Jack Szostak and co-workers at the Massachusetts General Hospital, Boston, have shown in model experiments that so-called proto- cells ( ie vesicles consisting of single fatty acids, fatty alcohols and fatty acid esters of glycerol ), the following properties ( in combination) show: You are thermodynamically stable between 0 and 100 ° C; they may include DNA and RNA polymers inside; they allow denaturation (separation ) of the polynucleotide strands at elevated temperature without loss of single strands from the Proto cell; they can non-specific ( that is, without transmembrane transport systems, eg proteins ) and very fast charged molecules such as nucleotides record.

The RNA World

The RNA world hypothesis, which goes back to the results from the Miller - Urey experiment and was formulated by Carl Woese first time in 1967, stating that a world of chemical with life based on ribonucleic acid (RNA) as a universal building block for information storage and catalysis reactions preceded our present forms of life. It is a link between more fundamental hypotheses of chemical evolution and the emergence of the first cellular life forms, such as Ribozyten. As part of the RNA world hypothesis it is believed that free or cell-bound RNA was replaced by the information storage medium chemically stable DNA and proteins functionally flexible in the evolution. As an indication of the existence of the RNA world ribosome and the catalytically active ribosomal RNA are considered, the evolutionary remnant of this period to constitute.

Alternative options considered

Biomolecules from space

The earth has been suspended since the beginning of their existence from the bombardment of comets and meteorites, especially in a Great bombardment ( Late Heavy Bombardment ) designated the first phase after the creation of Earth. In several meteorites simple organic molecules were detected, among other amino acids. If one considers the homochirality terrestrial biomolecules (L -amino acids and D-sugars ), it might be a possible explanation is that the amino acids come from outer space, as some of these meteoritic amino acids demonstrated an excess of the L-type by up to 9% been. The distribution is, however, also be explained by inorganic solid catalysts on the earth. Through experiments in which space conditions were simulated, has meanwhile been demonstrated that basic organic biomolecules, in particular amino acids, may also occur under such conditions.

It has now been demonstrated experimentally that meteorites such as the Murchison meteorite have catalytic capabilities: their material can cause arise from simple molecules such as formamide, among other amino acids and precursors of sugar molecules.

Black Smoker

Black smokers are hot water springs of the deep sea. There is a potentially favorable environment for the chemoautotrophic origin of life. This thesis is represented in particular by researchers William Martin and Michael Russell.

More perspectives

The panspermia hypothesis represents essentially the opinion that the first living things came to earth by ' seeding ' the earth with lower, bacteria-like life forms from outer space.

The hypothesis that lower life forms have come from space to Earth, shifts the problem of the origin of life but only to another place and is no explanation for the origin of life.

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