Life appeared on Earth more than 3.5 billion years ago – more precisely to designate the moment it’s hard though, because it is not easy to draw the line between “almost alive” and “alive.” However, you can say exactly what this magical moment lasted for many long millions of years. Still, it was a miracle.
To appreciate this miracle of dignity, it is necessary to get acquainted with a number of modern theories that describe the different variants and stages of birth. From brisk, but a lifeless set of simple organic compounds and to protoorganisms who know death and entered into an endless race of biological variability. In the end, do not these two terms – variability, and death – generate the entire amount life?..
1.Panspermia
The hypothesis that the placing of life on Earth from other celestial bodies has a lot of reputable defenders. In this position stood the great German scientist Hermann Helmholtz and the Swedish chemist Svante Arrhenius, the Russian thinker Vladimir Vernadsky and albert Lord Kelvin, physicist. However, science – an area of facts, and after the discovery of cosmic radiation and its harmful effect on all living panspermia seemed to have died.
But the deeper scientists plunge into matter, the more POPs up nuances. So, now – including putting many experiments on the spacecraft – we are far more serious about the ability of living organisms to tolerate radiation and cold, lack of water and other “charms” stay in outer space. Findings of various organic compounds on asteroids and comets in distant clusters of gas and dust, protoplanetary clouds and many no doubt. But the statement about finding in them traces of something suspiciously reminiscent of the microbes remain unproven.
It is easy to notice that, for all its fascination, the theory of panspermia only transfers the question of the origin of life in another place and another time. Whatever brought the first organisms on Earth – if by chance a meteorite or a cunning plan advanced aliens, they had somewhere and somehow been born. Let not here, much further in the past – but life had to grow out of lifeless matter. The question “How?” remains.
1.Unscientific: Spontaneous Generation
Highly spontaneous origin of living matter from nonliving – as the origin of maggots in rotting meat can be linked even to Aristotle, who summarized the thoughts of many predecessors and formed a coherent doctrine of spontaneous generation. Like other elements of the philosophy of Aristotle, spontaneous generation was the dominant doctrine in Medieval Europe and enjoyed a degree of support until the experiments of Louis Pasteur, who conclusively showed that the appearance of even maggots need flies-parents. Do not confuse spontaneous generation with current theories of the abiogenic origin of life: the difference between them is fundamental.
2. Primordial soup
This concept is closely linked to managed to acquire the status of classic experiments performed in the 1950s Stanley Miller and Harold Urey. In the laboratory, scientists have simulated the conditions that could exist at the surface of the young Earth, a mixture of methane, carbon monoxide and molecular hydrogen, numerous electrical discharges, ultraviolet light, and soon more than 10% of the carbon from the methane is in the form of certain organic molecules. In the experiments of Miller – Urey was obtained more than 20 amino acids, sugars, lipids and precursors of nucleic acids.
Modern variations of these classical experiments use much more complicated formulation, which more accurately correspond to the conditions of the early Earth. Simulated effects of volcanoes, their emissions of hydrogen sulfide and sulfur dioxide, the presence of nitrogen, So scientists can get a huge and varied amount of organic matter – potential potential building blocks of life. The main issue of these experiments remains a racemate: the isomers of optically active molecules (such as amino acids) are formed in the mixture in equal quantities, whereas all known life (with a few strange exceptions) includes only L-isomers.
However, to this problem we still will return. Here I should add that recently in 2015 – Cambridge Professor John Sutherland (John Sutherland) with his team showed the possibility of formation of all the basic “molecules of life”, components of DNA, RNA and proteins from a very simple set of source components. The main characters of this mixture, hydrogen cyanide and hydrogen sulfide, is not so rare in space. To them it is necessary to add some minerals and metals, in sufficient quantity available on Earth, such as phosphates, salts of copper and iron. Scientists built a detailed scheme of reactions, which could create a rich “primordial soup” in order that it appeared to the polymers and the game entered full chemical evolution.
The abiogenic hypothesis of the origin of life from the “organic soup”, which was checked by the experiments of Miller and Urey, proposed in 1924, Soviet biochemist Alexander Oparin. And although the “dark years” of prosperity of lysenkovshina scientist took the side of the opponents of the science of genetics, his merits are great. In recognition of the role of the academician, his name is the main award of the International society for the scientific study of the origin of life (ISSOL), the Oparin Medal. The prize is awarded every six years, and at different times it was awarded Stanley Miller, and the great Explorer of chromosomes, Nobel laureate Jack Szostak. Recognizing the huge contribution and Harold Urey, in between the awarding of the Medal of ISSOL Oparin (every six years) awards the Medal of Yuri. It was something unique, a true evolutionary prize – with a changing name.
3.Chemical evolution
The theory tries to describe the transformation of a relatively simple organic substances in rather complex chemical system, the predecessor of the actual life, under the influence of external factors, mechanisms of selection and self-organization. The basic concept of this approach is “water-carbon chauvinism”, representing these two components (water and carbon – NS) as absolutely essential and the key for the emergence and development of life, whether on Earth or somewhere beyond. But the main problem remain the conditions under which the “water-carbon chauvinism” may develop in a very sophisticated chemical complexes, capable above all of self-replication.
According to one hypothesis, the primary organization of molecules might occur in the micropores of clay minerals, which perform a structural role. This idea a few years ago put forward the Scottish chemist Alexander Cairns-Smith (Alexander Graham Cairns-Smith). On their inner surface, as in the matrix, could settle and polymerize complex biomolecules: Israeli scientists have shown that such conditions allow to grow long enough protein chain. Here can accumulate the desired amount of metal salts that play an important role of catalysts of chemical reactions. Clay walls can perform the function of cell membranes, separating “inside” the space in which the flow of increasingly complex chemical reactions, and separating it from the chaos outside.
“Matrices” for the growth of polymer molecules could serve as the surface of crystalline minerals: the spatial structure of their crystal lattice is capable of selecting only the optical isomers of the same type – for example, L-amino acids, – solving the problem, which we discussed above. Energy for primary “metabolism” could put inorganic reactions such as the restoration of the mineral pyrite (FeS2) by hydrogen (up to iron sulfide and hydrogen sulfide). In this case, for the emergence of complex biomolecules is not required nor lightnings, ultraviolet radiation, as in the experiments of Miller – Urey. And that means we can get rid of the bad aspects of their actions.
Young Earth were not protected from the harmful – and even deadly – components of solar radiation. Even today, experienced the evolution of organisms would be unable to withstand the hard UV – despite the fact that the Sun was much younger and did not give enough heat to the planet. This led to the hypothesis that in an age when happened the miracle of the origin of life, the whole Earth could be covered with a thick – hundreds of meters – a layer of ice and it’s for the best. Underneath this ice sheet, life can feel completely safe from ultraviolet radiation, and from the frequent meteorite strikes that threatened to destroy it in the Bud. Relatively cool environment could also stabilize the structure of the first macromolecules.
4. Black smokers
In fact, ultraviolet radiation on the young Earth, the atmosphere which lacked oxygen and had such wonderful things as the ozone layer was supposed to be a killer for any nascent life. Out of this grew the suggestion that the ancestors of the fragile living organisms had to exist somewhere, hiding from the continuous flow of sterilizing everything rays. For example, deep water – course, where there is sufficient mineral substances, mixing, heat and energy for chemical reactions. And such places are found.
Towards the end of the twentieth century, it became clear that the ocean floor can not be a haven of medieval monsters: the conditions are too severe, the temperature is small, and there is no radiation, and rare organics that settle from the surface. In fact, this vast semi-desert – with a few notable exceptions there in deep water, near the exits of geothermal resources, life literally abounds. Rich sulfides black water hot, actively mixed and contains a lot of minerals.
Black smokers of the ocean – a very rich and distinctive ecosystems: feeding on them bacteria use gelaterie reaction, which we have already spoken. They are the basis for full flowering of life, including a lot of unique worms and shrimp. Perhaps they were the basis and the origin of life on the planet: at least, theoretically, such a system carry.
2.Unscientific: the Spirits, gods, ancestors
Any cosmological myths about the origin of the world always get married antropologicheskie – about the origin of man. And in these fantasies, we can only envy the imagination of ancient authors: the question of what, how and why any space, where and how did life – and people – version sounded very different and almost always beautiful. Plants, fish and animals were caught from the sea floor, a huge Raven, people would crawl out the worms from the body of that ancestor Pangu, clay and ashes, born from the marriage of gods and monsters. All this is surprisingly poetic, but to science, of course, irrelevant.
5.The world of RNA
In accordance with the principles of dialectical materialism life is “unity and struggle” of the evolving and inherited information, on the one hand, and biochemical and structural functions. One without the other is impossible – and the question of where life began, with information and nucleic acids or with functions and proteins remains one of the most difficult. And one of the known solutions to this paradoxical problem is the hypothesis of the “RNA world”, which appeared in the late 1960s and finally took shape in the late 1980s.
RNA macromolecules in storage and transfer of information is not as effective as DNA, and in the performance of the enzymatic function – not as impressive as protein. But RNA molecules are capable, and another, and still they are the transmission link in the information exchange of cells, and catalyze a number of reactions in her. Proteins unable to replicate without DNA, and DNA is unable to do without protein “skills”. RNA can be fully Autonomous: it is able to catalyze its own “reproduction” – for a start it’s enough.
Research in the framework of the hypothesis of “RNA world” showed that these macromolecules are able to complete chemical evolution. Take a good example, demonstrated biophysically California, led by Leslie Angelom (Lesley Orgel): if a solution is capable of self-replication of RNA to add ethidium bromide, used to this system poison that blocks the synthesis of RNA, then slowly, with the change of generations of macromolecules in the mixture appear to RNA, is resistant even to very high concentrations of toxin. Approximately so, by evolution of the first RNA molecules could find a way to synthesize the first tools-proteins, and then in conjunction with them – “open” for themselves and the DNA double helix, the ideal carrier of genetic information.
3.Unscientific: Immutability
Not more scientific than the stories about the forefathers can be called and the looks of wearing big name Theory steady state. According to its supporters, is no life at all never had any – not born and the Earth, appearing and space: they just always was, always will be. All this is not more justified than worms Pangu to seriously accept such a “theory”, you have to forget about the countless findings of paleontology, Geology and astronomy. And in fact, give up all the grandiose buildings of modern science – but then, perhaps I should abandon all that relies to its residents, including computers and painless dental treatment.
6.Protocells
However, a simple replication to “normal life” is not enough: every life is, above all, spatially isolated portion of the medium separating the processes of exchange, facilitating for some of the reactions and to avoid others. In other words, life is the cell bounded by a semi-permeable membrane consisting of lipids. And “protocell” was supposed to appear at the earliest stages of life on Earth – the first hypothesis about their origin expressed by the familiar Alexander Oparin. In his presentation “protoberberine” could be droplets of hydrophobic lipids, resembling yellow drops of oil floating in the water.
The whole idea of the scientist are accepted by modern science, had worked on the issue and Jack Szostak, who received for his work the Oparin Medal. Together with Anamalai Katarzyna (Katarzyna Adamala) he managed to create a kind of model “protocells”, the analogue of the membrane which is comprised of modern lipids, and even more simple organic molecules, fatty acids, which could accumulate in places the appearance of the first protoorganisms. The Shostak and Adamle even managed to “revive” their structures, adding to the environment of magnesium ions (stimulating RNA polymerases) and citric acid (a stabilizing structure of fatty membranes).
In the end they turned out quite simple, but in some living system anyway, it was a normal protocell that contained the protected membrane environment for the reproduction of RNA. From this point you can close the last Chapter of the history of life and begin the first Chapter of its history. However, that’s another topic, so we will tell only one, but extremely important concept, related to the first steps of the evolution of life and the emergence of a huge diversity of organisms.
4.Unscientific: the Eternal return
“Branded” presentation of Indian philosophy, Western philosophy associated with the writings of Immanuel Kant, Friedrich Nietzsche, and Mircea Eliade. A poetic picture of the eternal journey of every living soul in the infinite number of worlds and their inhabitants, its rebirth in the small insect, the sublime poet, and even a creature unknown to us, demon, or God. Despite the lack of ideas of reincarnation, Nietzsche this idea is really close: eternity is eternal, and therefore any event it can and should happen again. And each creature without end rotates on the carousel universal return, so only the dizzy and the problem of the primary origin disappears somewhere in the kaleidoscope of countless repetitions.
7. Endosymbiont
Look at yourself in the mirror, look into my eyes: the creature that you look at each other, is a complex hybrid that arose in ancient times. At the end of the nineteenth century German-English naturalist Andreas Schimper (Andreas Schimper) noticed that the chloroplasts – organelles in plant cells responsible for photosynthesis – are replicated separately from the cells. Shortly afterwards, the hypothesis that the chloroplast is the symbionts, cells of photosynthetic bacteria, once ingested by the host and left to live here forever.
Of course, chloroplasts we have, otherwise we could eat sunlight, as suggested by some pseudo-religious sects. However, in the 1920s hypothesis endosymbiosis was extended to include mitochondria – organelles that consume oxygen and supply energy to all our cells. To date, this hypothesis has acquired the status of a full-fledged, proven theory – suffice it to say that mitochondrial and plastid genome revealed own more or less independent of the mechanisms of cell division and its own system of protein synthesis.
In nature and other found endosymbiont, not having behind billions of years of evolution and located at a less deep level of integration in the cell. For example, some amoebae do not own mitochondria, but is included inside performing their role of bacteria. There are hypotheses and endosymbiotic about the origin of other organelles, including flagella and cilia, and even the cell nucleus: according to the opinion of some researchers, we all eukaryotes, are the result of an unprecedented merger between bacteria and archaea. These versions until I find the strict validation, but one thing is clear: having hardly arisen, life began to absorb neighbors and interact with them, giving birth to new life.
5.Unscientific: Creationism
The notion of creationism arose in the nineteenth century when the word began to be called supporters of various versions of the appearance of the world and life, proposed by the authors of the Torah, the Bible and other Holy books of monotheistic religions. However, in fact, nothing new in comparison with these books, the creationists have not offered, over and over again trying to deny the strict and thorough findings of science – and in fact, repeatedly losing one position after another. Unfortunately, the idea of the modern pseudo-creationists, much easier to understand: awareness of the theories of this science need to spend a lot of effort.
