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Notes. In the beginning Comparewith in which the order of events is entirely different.The Genesis 1 account conflicts with the order of events that are known to science.The earth and 'heaven' are created together 'in the beginning,' whereas according tocurrent estimates, the earth and universe are about 4.6 and 13.8 billion years old, respectively.Also in the first creation account, the earth is created before light, sun and stars; birds and whales beforereptiles and insects; and flowering plants before any animals. The order of events known fromscience is in each case just the opposite. Let there be light. These are God's first spoken words. It's not clear who he was talking to.God continues to talk (to himself?) throughout the creation process. (See verses, and.)But after creating animals, God stops talking to himself and begins talking to them.
(See.). The first day When did the first day begin? Did God create heaven and earth beforeor during the first day? And when did his spirit move on the waters? Did day 1 begin withthe creation of light?It's impossible to tell from the text, but it seems more likely that God began his workweekwith with the creaion of light.
So I'm calling everything before that 'Day Zero'. God divided the light from the darkness. Yet he didn't make the light producing objects (the sun and the stars) until the fourthday.And how could there be 'the evening and the morning' on the first day if there wasno sun to mark them?. A firmament God spends one-sixth of his entire creativeeffort (the second day) working on a solid firmament. This strange structure,which God calls heaven, is intended to separate the higher waters from the lowerwaters. Let the earth bring forth grass.
Plants are made on the third day before there was a sunto drive their photosynthetic processes.God lets 'the earth bring forth' the plants, rather thancreating them directly. Maybe Genesis is not so anti-evolution after all. Let them be for signs.
God placed the sun, moon, and stars in the firmament so that they can be used 'for signs'.This, of course, is exactly what astrologers do: read 'the signs' in theZodiac to predict what will happen on Earth. God made two great lights. But the moon is not a light; it only reflects light from the sun. And why, if God made the moon to'rule the night', does it spend half of its time moving through the daytime sky?. He made the stars also. God spends a day making light (before making the sun and stars) and separating light from darkness; then, at the end of a hard day's work, and almost as an afterthought, he makes. To give light upon the earth Then why is only a tiny fraction of stars visible from earth?
Under thebest conditions, no more than a few thousand stars are visible with the unaided eye, yet thereare hundreds of billions of stars in our galaxy and a hundred billion or so galaxies. Were theyall created 'to give light upon the earth'?. Let the waters bring forth abundantly the moving creaturethat hath life, and fowl. Notice that the waters brought forth the living creatures - God didn't create them directly.The samelanguage is used to describe the origin of land animals in andplants in. God made the beast of the earth.
God said, Let us make man in our image. Let them have dominion. This couldn't be true, of course,since millions of other species existed for millions of years before humans existed. But this verse is usedby fundamentalist Christians to justify their mistreatment of other species and disregard for the environment.After all, they believe that God created the other species just for them, so they can do whatever they please with them. Male and female created he them.
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God created humans - male and female - in his own image. So does thismean that God is both male and female?. Be fruitful, and multipl.y This verse is used to justify Christian opposition to birth control. I have given you every herb.
And every tree. Since many plants have evolved poisons to protect against animals that would like to eat them, God's advice is more than a little reckless.Would you tell your children to go out in the garden and eat whatever plants they encounter? Of course not. But then, you are much nicerand smarter than God. To every beast. I have given every green herb for meat. All animals were originally herbivores.
Tapeworms, vampire bats, mosquitoes, and barracudas - all were strictvegetarians, as created by God. Behold, it was very good.
The on are putative fossilized, found in, that may have lived as early as 4.28 billion years ago, relatively soon after the, and not long after the 4.54 billion years ago.Abiogenesis, or informally the origin of life, is the process by which has arisen from non-living matter, such as simple. While the details of this process are still unknown, the prevailing scientific hypothesis is that the transition from non-living to living entities was not a single event, but an evolutionary process of increasing complexity that involved molecular, and the emergence of. Although the occurrence of abiogenesis is uncontroversial among scientists, its possible mechanisms are poorly understood. There are several principles and hypotheses for how abiogenesis could have occurred.Researchers study abiogenesis through a combination of, and, and aim to determine how pre-life gave rise to life.
The study of abiogenesis can be, or, with more recent approaches attempting a synthesis of all three, as life arose under conditions that are strikingly different from those on Earth today. Life functions through the specialized chemistry of and and builds largely upon four key families of chemicals: (fatty cell walls), (sugars, cellulose), (protein metabolism), and (self-replicating DNA and RNA).
Any successful theory of abiogenesis must explain the origins and interactions of these classes of molecules. Many approaches to abiogenesis investigate how, or their components, came into existence. Researchers generally think that current life descends from an, although other self-replicating molecules may have preceded RNA.The classic 1952 and similar research demonstrated that most amino acids, the chemical constituents of the used in all living organisms, can be synthesized from under conditions intended to replicate those of the. Scientists have proposed various external sources of energy that may have triggered these reactions, including. Other approaches ('metabolism-first' hypotheses) focus on understanding how in chemical systems on the early Earth might have provided the necessary for self-replication.The alternative speculates that arose outside Earth by unknown mechanisms, and spread to the early Earth on.
It is known that complex occur in the and in, and these molecules may have provided for the development of life on Earth. An extreme speculation is that the of life could have begun as early as 17 million years after the, during a, and that life may exist throughout the.Earth remains the only place in the known to harbour life, and informs most studies of abiogenesis.
The is approximately 4.54 billion years; the earliest undisputed evidence of life on Earth dates from at least 3.5 billion years ago, and possibly as early as the Era (between 3.6 and 4.0 billion years ago), after geological started to solidify following the molten. In May 2017 scientists found possible evidence of early life in 3.48-billion-year-old and other related mineral deposits (often found around and ) uncovered in the of. However, a number of discoveries suggest that life may have appeared on Earth even earlier. As of 2017, or fossilised, within dated from 3.77 to 4.28 billion years old found in rocks in may harbour the oldest record of life on Earth, suggesting life started soon after. According to biologist, 'If life arose relatively quickly on Earth then it could be common in the universe.' However, in contrast to the simpler referred to by Hedges, may be so rare that humankind's nearest neighbors may be beyond the possibility of our ever contacting them.
Astronomer, of the, said that the factors of the (which estimates the possibility of communicating with other technically intelligent life) are a means of organizing our lack of knowledge. See also:Soon after the, which occurred roughly 14 billion years ago, the only chemical elements present in the universe were hydrogen, helium, and lithium, the three lightest atoms in the periodic table. These elements gradually came together to form stars. These early stars were massive and short-lived, producing heavier elements through.
As these stars reached the end of their, they ejected these heavier elements, among them carbon and oxygen, throughout the universe. These heavier elements allowed for the formation of new objects, including rocky planets and other bodies. According to the, the formation and evolution of the began 4.6 with the of a small part of a giant. Most of the collapsing mass collected in the center, forming the, while the rest flattened into a out of which the, and other formed. The Earth, 4.5 billion years ago, was at first inhospitable to any living organisms. Based on numerous observations and studies of the, the Earth is thought to have had a, formed through of the rocks that accumulated from.
At first, it was thought that the Earth's consisted of hydrogen compounds—, and —and that life began under such conditions, which are conducive to the formation of organic molecules. According to later models, suggested by studying ancient minerals, the atmosphere in the late Hadean period consisted largely of, and, with smaller amounts of, and compounds. During its formation, the Earth lost a significant part of its initial mass, with a nucleus of the heavier rocky elements of the protoplanetary disk remaining. As a consequence, Earth lacked the to hold any molecular hydrogen in its atmosphere, and rapidly lost it during the Hadean period, along with the bulk of the original inert gases.
The solution of carbon dioxide in water is thought to have made the seas slightly, giving them a of about 5.5. The atmosphere at the time has been characterized as a 'gigantic, productive outdoor chemical laboratory.' It may have been similar to the mixture of gases released today by volcanoes, which still support some abiotic chemistry.may have in the Hadean Eon, as soon as two hundred million years (200 ) after the Earth formed, in a hot 100 °C (212 °F) reducing environment, and the pH of about 5.8 rose rapidly towards neutral. This scenario has found support from the dating of 4.404 -old crystals from metamorphosed of in the Western Australia of the, which provide evidence that oceans and existed within 150 of Earth's formation. Despite the likely increased volcanism and existence of many smaller 'platelets,' it has been suggested that between 4.4 and 4.3 Ga (billion years), the Earth was a water world, with little if any continental crust, an extremely atmosphere and a subject to intense (UV) light, from a, and continued impacts.The Hadean environment would have been highly hazardous to modern life. Frequent collisions with large objects, up to 500 kilometres (310 mi) in diameter, would have been sufficient to sterilize the planet and vaporize the oceans within a few months of impact, with hot steam mixed with rock vapour becoming high altitude clouds that would completely cover the planet.
After a few months, the height of these clouds would have begun to decrease but the cloud base would still have been elevated for about the next thousand years. After that, it would have begun to rain at low altitude. For another two thousand years, rains would slowly have drawn down the height of the clouds, returning the oceans to their original depth only 3,000 years after the impact event. Earliest biological evidence for life. For branching of Bacteria phyla, see.The most commonly accepted location of the root of the tree of life is between a monophyletic domain and a clade formed by and of what is referred to as the 'traditional tree of life' based on several molecular studies starting with. A very small minority of studies have concluded differently, namely that the root is in the domain Bacteria, either in the phylum or that the phylum is basal to a clade with Archaea+Eukaryotes and the rest of Bacteria as proposed. More recently, has proposed an alternative view which is rooted in abiotic RNA synthesis which becomes enclosed within a capsule and then creates RNA replicates.
It is proposed that this then bifurcates between Dominion Ribosa , and after the loss of ribozymes RNA viruses as Domain Viorea, and Dominion Terroa , which after creating a large cell within a lipid wall, creating DNA the 20 based amino acids and the triplet code, is established as the or LUCA, of earlier phylogenic trees. In the Siyeh Formation,. In 2002, a paper in the scientific journal suggested that these 3.5 (billion years) old geological formations contain fossilized. This suggests they are evidence of one of the on.The earliest life on Earth existed more than 3.5 billion years ago, during the Era when sufficient crust had solidified following the molten Hadean Eon. The earliest physical evidence so far found consists of in the of Northern Quebec, in ' rocks at least 3.77 billion and possibly 4.28 billion years old.
This finding suggested life developed very soon after oceans formed. The structure of the microbes was noted to be similar to bacteria found near in the modern era, and provided support for the hypothesis that abiogenesis began near hydrothermal vents.Also noteworthy is biogenic graphite in 3.7 billion-year-old metasedimentary rocks from southwestern Greenland and fossils found in 3.48 billion-year-old sandstone from Western Australia. Evidence of early life in rocks from Island, near the in southwestern Greenland, dating to 3.7 billion years ago have shown biogenic carbon. In other parts of the Isua supracrustal belt, graphite inclusions trapped within crystals are connected to the other elements of life: oxygen, nitrogen, and possibly phosphorus in the form of phosphate, providing further evidence for life 3.7 billion years ago. At Strelley Pool, in the region of Western Australia, compelling evidence of early life was found in -bearing sandstone in a fossilized beach, that showed rounded tubular cells that oxidized sulfur by in the absence of oxygen. Further research on from Western Australia in 2015 suggested that life likely existed on Earth at least 4.1 billion years ago.Traditionally it was thought that during the period between 4.28 and 3.8 Ga, changes in the orbits of the may have caused a by asteroids and that pockmarked the and the other inner planets (, and presumably Earth and ). This would likely have repeatedly sterilized the planet, had life appeared before that time.
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Geologically, the Hadean Earth would have been far more active than at any other time in its history. Studies of suggests that such as with a of 7.17×10 5 (717 thousand) years, and with a half-life of 1.250×10 9 (1.25 billion) years, isotopes mainly produced in, were much more common. Internal heating as a result of between the and the would have caused a great deal of, with the probable result of many more smaller and more active tectonic plates than now exist.The time periods between such devastating environmental events give time windows for the possible origin of life in the early environments. If the deep marine hydrothermal setting was the site for the origin of life, then abiogenesis could have happened as early as 4.0 to 4.2 Ga. If the site was at the surface of the Earth, abiogenesis could only have occurred between 3.7 and 4.0 Ga.In 2016, a set of 355 likely present in the (LUCA) of all was identified. A total of 6.1 million prokaryotic protein coding genes from various phylogenic trees were sequenced, identifying 355 protein clusters from amongst 286,514 protein clusters that were probably common to LUCA.
The results 'depict LUCA as, CO 2-fixing, H 2-dependent with a, N 2-fixing and thermophilic. LUCA's biochemistry was replete with FeS clusters and radical reaction mechanisms. Its reveal dependence upon,. Its genetic code required modifications and S-adenosylmethionine-dependent.'
The results depict as a basal clade in the 355 phylogenies examined, and suggest that LUCA inhabited an anaerobic setting in a geochemically active environment rich in H 2, CO 2 and iron. Brazier has shown that early micro-fossils came from a hot world of gases such as, and, which are toxic to much current life. Another analysis of the conventional threefold tree of life shows thermophilic and hyperthermophilic and are closest to the root, suggesting that life may have evolved in a hot environment.
Conceptual history Spontaneous generation. Main article:Traditional religion attributed the origin of life to supernatural deities who created the natural world. Spontaneous generation, the first naturalistic theory of life arising from non-life, goes back to and, and continued to have support in Western scholarship until the 19th century. Classical notions of spontaneous generation held that certain 'lower' or 'vermin' animals are generated by decaying organic substances. According to Aristotle, it was readily observable that arise from dew on plants, from putrid matter, mice from dirty hay, crocodiles from rotting sunken logs, and so on. A related theory was heterogenesis: that some forms of life could arise from different forms (e.g.
Bees from flowers). The modern scientist said that the basic idea of such theories was that life was continuously created as a result of chance events.In the 17th century, people began to question such assumptions. In 1646, published his (subtitled Enquiries into Very many Received Tenets, and commonly Presumed Truths), which was an attack on false beliefs and 'vulgar errors.'
His contemporary, erroneously refuted him, stating: 'To question this spontaneous generation, is to question Reason, Sense, and Experience: If he doubts of this, let him go to, and there he will find the fields swarming with mice begot of the mud of, to the great calamity of the Inhabitants.' In 1665, published the first drawings of a. Hooke was followed in 1676 by, who drew and described microorganisms that are now thought to have been. Many felt the existence of microorganisms was evidence in support of spontaneous generation, since microorganisms seemed too simplistic for, and through had not yet been observed.
Van Leeuwenhoek took issue with the ideas common at the time that fleas and lice could spontaneously result from, and that frogs could likewise arise from slime. Using a broad range of experiments ranging from sealed and open meat incubation and the close study of insect reproduction he became, by the 1680s, convinced that spontaneous generation was incorrect.
In 1879The first experimental evidence against spontaneous generation came in 1668 when showed that no appeared in meat when flies were prevented from laying eggs. It was gradually shown that, at least in the case of all the higher and readily visible organisms, the previous sentiment regarding spontaneous generation was false. The alternative hypothesis was: that every living thing came from a pre-existing living thing ( omne vivum ex ovo, Latin for 'every living thing from an egg'). In 1768, demonstrated that were present in the air, and could be killed by boiling.
In 1861, performed a series of experiments that demonstrated that organisms such as bacteria and fungi do not spontaneously appear in sterile, nutrient-rich media, but could only appear by invasion from without.By the middle of the 19th century, biogenesis had accumulated so much evidence in support that the alternative theory of spontaneous generation had been effectively disproven. Remarked, about a finding of his in 1864 which he considered definitive, 'Never will the doctrine of spontaneous generation recover from the mortal blow struck by this simple experiment.' Gave a mechanism by which life diversified from a few simple organisms to a variety of to complex forms. Today, scientists agree that all current life descends from earlier life, which has become progressively more complex and diverse through 's mechanism of by.However, the findings of on the origin of the universe in the Big Bang, and of geology on the origin of the Earth from interstellar gas, require a companion explanation for the origin of the first life from non-life. One of the first speculations on this subject was in Darwin's letter to on 1 February 1871, suggesting that the original spark of life may have begun in a 'warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity, &c., present, that a compound was chemically formed ready to undergo still more complex changes.' He went on to explain that 'at the present day such matter would be instantly devoured or absorbed, which would not have been the case before living creatures were formed.'
He had written to Hooker in 1863 stating that, 'It is mere rubbish, thinking at present of the origin of life; one might as well think of the origin of matter.' In, he had referred to life having been 'created', by which he 'really meant 'appeared' by some wholly unknown process', but had soon regretted using the Old Testament term 'creation'. Etymology. Main article:The term biogenesis is usually credited to either or to. Bastian used the term around 1869 in an unpublished exchange with to mean 'life-origination or commencement'. In 1870, Huxley, as new president of the, delivered an address entitled Biogenesis and Abiogenesis.
In it he introduced the term biogenesis (with an opposite meaning to Bastian's) as well as abiogenesis:And thus the hypothesis that living matter always arises by the agency of pre-existing living matter, took definite shape; and had, henceforward, a right to be considered and a claim to be refuted, in each particular case, before the production of living matter in any other way could be admitted by careful reasoners. It will be necessary for me to refer to this hypothesis so frequently, that, to save circumlocution, I shall call it the hypothesis of Biogenesis; and I shall term the contrary doctrine—that living matter may be produced by not living matter—the hypothesis of Abiogenesis.Subsequently, in the preface to Bastian's 1871 book, The Modes of Origin of Lowest Organisms, Bastian referred to the possible confusion with Huxley's usage and explicitly renounced his own meaning:A word of explanation seems necessary with regard to the introduction of the new term Archebiosis. I had originally, in unpublished writings, adopted the word Biogenesis to express the same meaning—viz., life-origination or commencement. But in the mean time the word Biogenesis has been made use of, quite independently, by a distinguished biologist Huxley, who wished to make it bear a totally different meaning. He also introduced the word Abiogenesis. I have been informed, however, on the best authority, that neither of these words can—with any regard to the language from which they are derived—be supposed to bear the meanings which have of late been publicly assigned to them. Wishing to avoid all needless confusion, I therefore renounced the use of the word Biogenesis, and being, for the reason just given, unable to adopt the other term, I was compelled to introduce a new word, in order to designate the process by which living matter is supposed to come into being, independently of pre-existing living matter.Since the end of the nineteenth century, 'evolutive abiogenesis' means increasing complexity and evolution of matter from inert to living states.
'Primordial soup' hypothesis. And (right) in 1938No new notable research or hypothesis on the subject appeared until 1924, when reasoned that atmospheric oxygen prevents the synthesis of certain organic compounds that are necessary building blocks for life. In his book The Origin of Life, he proposed (echoing Darwin) that the 'spontaneous generation of life' that had been attacked by Louis Pasteur did in fact occur once, but was now impossible because the conditions found on the early Earth had changed, and preexisting organisms would immediately consume any spontaneously generated organism.
Oparin argued that a 'primeval soup' of organic molecules could be created in an oxygenless atmosphere through the action of. These would combine in ever more complex ways until they formed droplets. These droplets would ' by fusion with other droplets, and ' through fission into daughter droplets, and so have a primitive in which factors that promote 'cell integrity' survive, and those that do not become. Main article:In trying to uncover the intermediate stages of abiogenesis mentioned by Bernal, in the 1950s and 1960s studied the spontaneous formation of structures (small chains of amino acids) under conditions that might plausibly have existed early in Earth's history.
In one of his experiments, he allowed amino acids to dry out as if puddled in a warm, dry spot in prebiotic conditions. He found that, as they dried, the amino acids formed long, often cross-linked, thread-like, submicroscopic molecules now named '.In another experiment to set suitable conditions for life to form, Fox collected volcanic material from a in. He discovered that the temperature was over 100 °C (212 °F) just 4 inches (100 mm) beneath the surface of the cinder cone, and suggested that this might have been the environment in which life was created—molecules could have formed and then been washed through the loose volcanic ash into the sea. He placed lumps of lava over amino acids derived from methane, ammonia and water, sterilized all materials, and baked the lava over the amino acids for a few hours in a glass oven. A brown, sticky substance formed over the surface, and when the lava was drenched in sterilized water, a thick, brown liquid leached out. The amino acids had combined to form, and the proteinoids had combined to form small globules that Fox called 'microspheres'. His proteinoids were not cells, although they formed clumps and chains reminiscent of, but they contained no functional or any encoded information.
Based upon such experiments, stated in December 1967 that 'laboratories will be creating a living cell within ten years,' a remark that reflected the typical contemporary naivety about the complexity of cell structures. Current models There is no single, generally accepted model for the origin of life. Scientists have proposed several plausible hypotheses, which share some common elements. While differing in the details, these hypotheses are based on the framework laid out by Alexander Oparin (in 1924) and by J. Haldane (in 1925), that the first molecules constituting the earliest cells 'were synthesized under natural conditions by a slow process of molecular evolution, and these molecules then organized into the first molecular system with properties with biological order'. Oparin and Haldane suggested that the atmosphere of the early Earth may have been chemically reducing in nature, composed primarily of methane (CH 4), ammonia (NH 3), water (H 2O), hydrogen sulfide (H 2S), carbon dioxide (CO 2) or carbon monoxide (CO), and (PO 4 3−), with molecular oxygen (O 2) and (O 3) either rare or absent.
According to later models, the atmosphere in the late Hadean period consisted largely of nitrogen (N 2) and carbon dioxide, with smaller amounts of carbon monoxide, hydrogen (H 2), and sulfur compounds; while it did lack molecular oxygen and ozone, it was not as chemically reducing as Oparin and Haldane supposed.Bernal coined the term biopoiesis in 1949 to refer to the origin of life. In 1967, he suggested that it occurred in three 'stages':. the origin of biological monomers.
the origin of biological polymers. the evolution from molecules to cellsBernal suggested that evolution commenced between stages 1 and 2. Bernal regarded the third stage—discovering methods by which biological reactions were incorporated behind a cell's boundary—as the most difficult.
Modern work on the way that self-assemble, and the work on micropores in various substrates, may be a key step towards understanding the development of independent free-living cells.The chemical processes on the pre-biotic early Earth are called. Both and demonstrated that evolution, including replication, variation, and, can occur in populations of molecules as well as in organisms. Following on from chemical evolution came the initiation of, which led to the first cells.
No one has yet synthesized a ' using simple components with the necessary properties of life (the so-called '). Without such a proof-of-principle, explanations have tended to focus on.
However, some researchers work in this field, notably. Others have argued that a ' is more feasible. Spiegelman took advantage of natural selection to synthesize the, which had a genome with just 218 bases, having deconstructively evolved from a 4500-base bacterial RNA. Eigen built on Spiegelman's work and produced a similar system further degraded to just 48 or 54 nucleotides—the minimum required for the binding of the replication enzyme.
And others at engineered existing prokaryotic cells with progressively fewer genes, attempting to discern at which point the most minimal requirements for life are reached.The NASA strategy on abiogenesis states that it is necessary to identify interactions, intermediary structures and functions, energy sources, and environmental factors that contributed to the diversity, selection, and replication of evolvable macromolecular systems. Emphasis must continue to map the chemical landscape of potential primordial informational. The advent of polymers that could replicate, store genetic information, and exhibit properties subject to selection likely was a critical step in the of prebiotic chemical evolution.In October 2018, researchers at announced the development of a new technology, called a, to help study the on planet and beyond. It consists of a sophisticated climate chamber to study how the building blocks of life were assembled and how these prebiotic molecules transitioned into self-replicating RNA molecules.
Chemical origin of organic molecules The, except for hydrogen and helium, ultimately derive from. In 2016, astronomers reported that the very basic chemical ingredients of —the (CH, or ), the carbon-hydrogen positive ion (CH+) and the carbon ion (C+)—are largely the result of from stars, rather than other forms of radiation from and, as thought earlier. Complex molecules, including organic molecules, form naturally both in space and on planets. There are two possible sources of organic molecules on the early Earth:.
Terrestrial origins – organic molecule synthesis driven by impact shocks or by other energy sources (such as UV light, coupling, or electrical discharges; e.g., Miller's experiments). Extraterrestrial origins – formation of organic molecules in, which rain down on planets. A demonstrating extreme at the base of the.Based on recent, the necessary for life may have formed in the of surrounding the before the formation of the Earth.
According to the computer studies, this same process may also occur around other that acquire. (Also see ).Estimates of the production of organics from these sources suggest that the before 3.5 Ga within the early atmosphere made available quantities of organics comparable to those produced by terrestrial sources.It has been estimated that the Late Heavy Bombardment may also have effectively sterilized the Earth's surface to a depth of tens of metres. If life evolved deeper than this, it would have also been shielded from the early high levels of ultraviolet radiation from the T Tauri stage of the Sun's evolution. Simulations of geothermically heated oceanic crust yield far more organics than those found in the Miller-Urey experiments.
In the deep, Everett Shock has found 'there is an enormous thermodynamic drive to form organic compounds, as and hydrothermal fluids, which are far from equilibrium, mix and move towards a more stable state.' Shock has found that the available energy is maximized at around 100–150 degrees Celsius, precisely the temperatures at which the bacteria and have been found, at the base of the closest to the (LUCA).The accumulation and concentration of organic molecules on a planetary surface is also considered an essential early step for the origin of life.
Main article:are substances that catalyze the production of themselves and therefore are 'molecular replicators.' The simplest self-replicating chemical systems are autocatalytic, and typically contain three components: a product molecule and two precursor molecules. The product molecule joins together the precursor molecules, which in turn produce more product molecules from more precursor molecules.
The product molecule catalyzes the reaction by providing a complementary template that binds to the precursors, thus bringing them together. Such systems have been demonstrated both in biological and in small organic molecules. Systems that do not proceed by template mechanisms, such as the self-reproduction of and, have also been observed.It has been proposed that life initially arose as autocatalytic chemical networks.
British wrote about autocatalysis as a potential explanation for the origin of life in his 2004 book. In his book, Dawkins cites experiments performed by Jr. And his colleagues in which they combined amino adenosine and with the autocatalyst amino adenosine triacid ester (AATE). One product was a variant of AATE, which catalyzed the synthesis of themselves. This experiment demonstrated the possibility that autocatalysts could exhibit competition within a population of entities with heredity, which could be interpreted as a rudimentary form of natural selection.In the early 1970s, Manfred Eigen and examined the transient stages between the molecular chaos and a self-replicating in a prebiotic soup. In a hypercycle, the storing system (possibly RNA) produces an, which catalyzes the formation of another information system, in sequence until the product of the last aids in the formation of the first information system. Mathematically treated, hypercycles could create, which through natural selection entered into a form of Darwinian evolution.
A boost to hypercycle theory was the discovery of capable of catalyzing their own chemical reactions. Main article:Homochirality refers to a geometric uniformity of some materials composed of units. Chiral refers to nonsuperimposable 3D forms that are mirror images of one another, as are left and right hands. Living organisms use molecules that have the same chirality ('handedness'): with almost no exceptions, amino acids are left-handed while nucleotides and are right-handed. Chiral molecules can be synthesized, but in the absence of a chiral source or a chiral, they are formed in a 50/50 mixture of both (called a racemic mixture).
Known mechanisms for the production of non-racemic mixtures from racemic starting materials include: asymmetric physical laws, such as the; asymmetric environments, such as those caused by light, or the Earth's rotation, during racemic synthesis, and.Once established, chirality would be selected for. A small bias in the population can be amplified into a large one by, such as in the. In asymmetric autocatalysis, the catalyst is a chiral molecule, which means that a chiral molecule is catalyzing its own production. An initial enantiomeric excess, such as can be produced by polarized light, then allows the more abundant enantiomer to outcompete the other.Clark has suggested that homochirality may have started in outer space, as the studies of the amino acids on the showed that is more than twice as frequent as its D form, and was more than three times prevalent than its D counterpart. Various chiral crystal surfaces can also act as sites for possible concentration and assembly of chiral monomer units into macromolecules. Compounds found on meteorites suggest that the chirality of life derives from abiogenic synthesis, since amino acids from meteorites show a left-handed bias, whereas sugars show a predominantly right-handed bias, the same as found in living organisms.
Self-enclosement, reproduction, duplication and the RNA world Protocells. The three main structures form spontaneously in solution: the (a closed bilayer), the and the bilayer.A protocell is a self-organized, self-ordered, spherical collection of proposed as a stepping-stone to the origin of life. A central question in evolution is how simple protocells first arose and differed in reproductive contribution to the following generation driving the evolution of life.
Although a functional protocell has not yet been achieved in a laboratory setting, there are scientists who think the goal is well within reach.Self-assembled are essential components of primitive cells. The requires that the universe move in a direction in which increases, yet life is distinguished by its great degree of organization. Therefore, a boundary is needed to separate from non-living matter. Researchers Irene A. Chen and Jack W. Szostak amongst others, suggest that simple physicochemical properties of elementary protocells can give rise to essential cellular behaviours, including primitive forms of differential reproduction competition and energy storage.
Such cooperative interactions between the membrane and its encapsulated contents could greatly simplify the transition from simple replicating molecules to true cells. Furthermore, competition for membrane molecules would favour stabilized membranes, suggesting a selective advantage for the evolution of cross-linked fatty acids and even the of today. Such would allow for metabolism within the membrane, the exchange of small molecules but the prevention of passage of large substances across it. The main advantages of encapsulation include the increased of the contained cargo within the capsule and the storage of energy in the form of an.A 2012 study led by Armen Y.
Mulkidjanian of Germany's, suggests that inland pools of condensed and cooled geothermal vapour have the ideal characteristics for the origin of life. Scientists confirmed in 2002 that by adding a clay to a solution of fatty acid micelles (lipid spheres), the clay sped up the rate of vesicles formation 100-fold.Another protocell model is the. First synthesized in 1963 from simple minerals and basic organics while exposed to sunlight, it is still reported to have some metabolic capabilities, the presence of, amino acids, phospholipids, and RNA-like molecules. However, the nature and properties of the Jeewanu remains to be clarified.Electrostatic interactions induced by short, positively charged, hydrophobic peptides containing 7 amino acids in length or fewer, can attach RNA to a vesicle membrane, the basic cell membrane.Researchers Tony Z. Jia and Kuhan Chandru have proposed that membraneless polyesters droplets could have been significant in the Origins of Life.
Given the 'messy' nature of prebiotic chemistry, the spontaneous generation of these combinatorial droplets may have played a role in early cellularization before the innovation of lipid vesicles. Protein function within and RNA function in the presence of certain polyester droplets was shown to be preserved within the droplets. Additionally, the droplets have scaffolding ability, by allowing lipids to assemble around them that may have prevented leakage of genetic materials.RNA world. Main article:Panspermia is the that exists throughout the, distributed by, and, also, by in the form of unintended. For example, planetary contamination by organisms like, which has shown resistance to methods usually used in.The panspermia hypothesis does not attempt to explain how life first originated, but merely shifts it to another planet or a comet. The advantage of an extraterrestrial origin of primitive life is that life is not required to have formed on each planet it occurs on, but rather in a single location, and then spread about the to other star systems via cometary and/or meteorite impact. Evidence for the hypothesis is scant, but it finds some support in studies of found in and in studies of microbes' survival in outer space tests.
(See also:.)Extraterrestrial organic molecules. Is one of the simplest organic compoundsAn organic compound is any member of a large class of gaseous, liquid, or solid chemicals whose molecules contain carbon. Carbon is the after hydrogen, and oxygen. Carbon is abundant in the Sun, stars, comets, and in the of most planets. Organic compounds are relatively common in space, formed by 'factories of complex molecular synthesis' which occur in and, and chemically evolve after reactions are initiated mostly. Based on, the complex organic molecules necessary for life may have formed on dust grains in the protoplanetary disk surrounding the Sun before the formation of the Earth. According to the computer studies, this same process may also occur around other stars that acquire planets.Observations suggest that the majority of organic compounds introduced on Earth by interstellar dust particles are considered principal agents in the formation of complex molecules, thanks to their peculiar activities.
Studies reported in 2008, based on 12C/ 13C of organic compounds found in the Murchison meteorite, suggested that the RNA component uracil and related molecules, including, were formed extraterrestrially. On 8 August 2011, a report based on studies of meteorites found on Earth was published suggesting DNA components (adenine, guanine and related organic molecules) were made in outer space. Scientists also found that the permeating the universe contains complex organics ('amorphous organic solids with a mixed – structure') that could be created naturally, and rapidly, by stars. Of suggested that these compounds may have been related to the development of life on Earth said that 'If this is the case, life on Earth may have had an easier time getting started as these organics can serve as basic ingredients for life.' The C 60 buckyball is a complex molecule that has been detected in nebulae.NASA announced in 2009 that scientists had identified another fundamental chemical building block of life in a comet for the first time, glycine, an amino acid, which was detected in material ejected from comet in 2004 and grabbed by NASA's probe.
Glycine has been detected in meteorites before. Carl Pilcher, who leads the commented that 'The discovery of glycine in a comet supports the idea that the fundamental building blocks of life are prevalent in space, and strengthens the argument that life in the universe may be common rather than rare.' Comets are encrusted with outer layers of dark material, thought to be a -like substance composed of complex organic material formed from simple carbon compounds after reactions initiated mostly by ionizing radiation. It is possible that a rain of material from comets could have brought significant quantities of such complex organic molecules to Earth. Amino acids which were formed extraterrestrially may also have arrived on Earth via comets. It is estimated that during the Late Heavy Bombardment, meteorites may have delivered up to five million of organic prebiotic elements to Earth per year.(PAH) are the most common and abundant of the known polyatomic molecules in the, and are considered a likely constituent of the.
In 2010, PAHs, along with (or '), have been detected in. In April 2019, scientists, working with the, reported the confirmed detection of the large and complex ionized molecules of (C 60) in the between the.In March 2015, NASA scientists reported that, for the first time, complex DNA and RNA organic compounds of life, including uracil, cytosine and, have been formed in the laboratory under outer space conditions, using starting chemicals, such as pyrimidine, found in meteorites. Pyrimidine, like PAHs, the most carbon-rich chemical found in the Universe, may have been formed in stars or in interstellar dust and gas clouds.
A group of Czech scientists reported that all four RNA-bases may be synthesized from formamide in the course of high-energy density events like extraterrestrial impacts. Lipid world. Main article:The theory postulates that the first self-replicating object was lipid-like. It is known that phospholipids form in water while under agitation—the same structure as in cell membranes. These molecules were not present on early Earth, but other long-chain molecules also form membranes. Furthermore, these bodies may expand (by insertion of additional lipids), and under excessive expansion may undergo spontaneous splitting which preserves the same size and composition of lipids in the two. The main idea in this theory is that the molecular composition of the lipid bodies is the preliminary way for information storage, and evolution led to the appearance of polymer entities such as RNA or DNA that may store information favourably.
Studies on vesicles from potentially prebiotic amphiphiles have so far been limited to systems containing one or two types of amphiphiles. This in contrast to the output of simulated prebiotic chemical reactions, which typically produce very heterogeneous mixtures of compounds.Within the hypothesis of a lipid bilayer membrane composed of a mixture of various distinct amphiphilic compounds there is the opportunity of a huge number of theoretically possible combinations in the arrangements of these amphiphiles in the membrane. Among all these potential combinations, a specific local arrangement of the membrane would have favoured the constitution of a hypercycle, actually a positive composed of two mutual catalysts represented by a membrane site and a specific compound trapped in the vesicle. Such site/compound pairs are transmissible to the daughter vesicles leading to the emergence of distinct of vesicles which would have allowed Darwinian natural selection. Polyphosphates A problem in most scenarios of abiogenesis is that the thermodynamic equilibrium of amino acid versus peptides is in the direction of separate amino acids. What has been missing is some force that drives polymerization. The resolution of this problem may well be in the properties of.
Polyphosphates are formed by polymerization of ordinary monophosphate ions PO 4 −3. Several mechanisms of organic molecule synthesis have been investigated. Polyphosphates cause polymerization of amino acids into peptides. They are also logical precursors in the synthesis of such key biochemical compounds as (ATP). A key issue seems to be that calcium reacts with soluble phosphate to form insoluble , so some plausible mechanism must be found to keep calcium ions from causing precipitation of phosphate. There has been much work on this topic over the years, but an interesting new idea is that meteorites may have introduced reactive phosphorus species on the early Earth. PAH world hypothesis.
Also occasionally called biopoiesis (Bernal, 1960, p. 30). The reactions are:FeS + H 2S → FeS 2 + 2H + + 2e − FeS + H 2S + CO 2 → FeS 2 + HCOOH.
The reactions are:Reaction 1: Fayalite + water → magnetite + aqueous silica + hydrogen3Fe 2SiO 4 + 2H 2O → 2Fe 3O 4 + 3SiO 2 + 2H 2 Reaction 2: Forsterite + aqueous silica → serpentine3Mg 2SiO 4 + SiO 2 + 4H 2O → 2Mg 3Si 2O 5(OH) 4 Reaction 3: Forsterite + water → serpentine + brucite2Mg 2SiO 4 + 3H 2O → Mg 3Si 2O 5(OH) 4 + Mg(OH) 2Reaction 3 describes the hydration of olivine with water only to yield and Mg(OH) 2. Serpentine is stable at high pH in the presence of brucite like calcium silicate hydratephases formed along with (Ca(OH) 2) in hardened paste after the hydration of (Ca 2SiO 4), the artificial calcium equivalent of forsterite.Analogy of reaction 3 with belite hydration in ordinary Portland cement: Belite + water → C-S-H phase + portlandite 2 Ca 2SiO 4 + 4 H 2O → 3 CaO 2 SiO 2 3 H 2O + Ca(OH) 2Citations.
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