theories of origin of life wikipedia

It is likely that the ancestral ribosome was composed entirely of RNA, although some roles have since been taken over by proteins.

These compact structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed. The product molecule joins together the precursor molecules, which in turn produce more product molecules from more precursor molecules. The RNA world hypothesis describes an early Earth with self-replicating and catalytic RNA but no DNA or proteins. [195] The use of PAHs has also been proposed as a precursor to the RNA world in the PAH world hypothesis. [304] A model for the origin of life using clay was forwarded by Alexander Cairns-Smith in 1985 and explored as a plausible mechanism by several scientists. [165], There is no single generally accepted model for the origin of life. Studies have shown that populations of random atoms, when exposed to energy, will shuffle and organise themselves to dissipate energy more efficiently. Montmorillonite, an abundant clay, is a catalyst for the polymerization of RNA and for the formation of membranes from lipids. Bernal said on the Miller–Urey experiment that, it is not enough to explain the formation of such molecules, what is necessary, is a physical-chemical explanation of the origins of these molecules that suggests the presence of suitable sources and sinks for free energy. Part C: The Realistic Hypercycle", International Journal of Molecular Sciences, "The Emergence of Cells During the Origin of Life", "Coupled Phases and Combinatorial Selection in Fluctuating Hydrothermal Pools: A Scenario to Guide Experimental Approaches to the Origin of Cellular Life", "Histochemical localisation of RNA-like material in photochemically formed self-sustaining, abiogenic supramolecular assemblies 'Jeewanu, "Peptide glue may have held first protocell components together", "Electrostatic Localization of RNA to Protocell Membranes by Cationic Hydrophobic Peptides", "Letter no. Stan Palasek suggested based on a theoretical model that self-assembly of ribonucleic acid (RNA) molecules can occur spontaneously due to physical factors in hydrothermal vents. [84] More recently, Peter Ward has proposed an alternative view which is rooted in abiotic RNA synthesis which becomes enclosed within a capsule and then creates RNA ribozyme replicates.

Radioactive monazite material also has released soluble phosphate into the regions between sand-grains, making it biologically "accessible." These are seen to form micro-spheres which are observed to behave similarly to membrane-enclosed compartments. The analysis by Prigogine showed that if a system were left to evolve under an imposed external potential, material could spontaneously organize (lower its entropy) forming what he called "dissipative structures" which would increase the dissipation of the externally imposed potential (augment the global entropy production). [263] Furthermore, recent studies have found that the repeated actions of dehydration and rehydration trapped biomolecules like RNA inside the lipid protocells found within hot springs and providing the necessary preconditions for evolution by natural selection. [195] While life is, by definition, alive, artificial life is generally referred to as data confined to a digital environment and existence. [216][217] Polyphosphates are formed by polymerization of ordinary monophosphate ions PO43-. The totality of fossils, both discovered and undiscovered, and their placement in fossil-containing rock formations and sedimentary layers (strata) is known as the fossil record. As early as the 1860s, experiments have demonstrated that biologically relevant molecules can be produced from interaction of simple carbon sources with abundant inorganic catalysts. 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[243], Autocatalysts are substances that catalyze the production of themselves and therefore are "molecular replicators." LUCA's biochemistry was replete with FeS clusters and radical reaction mechanisms. Photoanomerization with UV light allows for inversion about the 1' anomeric centre to give the correct beta stereochemistry.

The centrality of the Krebs cycle (citric acid cycle) to energy production in aerobic organisms, and in drawing in carbon dioxide and hydrogen ions in biosynthesis of complex organic chemicals, suggests that it was one of the first parts of the metabolism to evolve. Organisms may be consumed by a predator or a scavenger and leftover organic material may then be further decomposed by detritivores, organisms that recycle detritus, returning it to the environment for reuse in the food chain.


However, the new research from MIT is backed up by mathematical and scientific evidence. James Gould: Most dictionaries define life as the property that distinguishes the living from the dead, and define dead as being deprived of life.

Bacteria and Archaea are two domains of prokaryotes. [172] Alternative hypothetical types of biochemistry have been proposed that eliminate one or more of these elements, swap out an element for one not on the list, or change required chiralities or other chemical properties. Small red dwarfs have the opposite problem, with a smaller habitable zone that is subject to higher levels of magnetic activity and the effects of tidal locking from close orbits. depict LUCA as anaerobic, CO2-fixing, H2-dependent with a Wood–Ljungdahl pathway, N2-fixing and thermophilic. Abiogenesis or biopoiesis is the natural process of life arising from non-living matter such as simple organic compounds. Extinction is the process by which a group of taxa or species dies out, reducing biodiversity. [16] Many approaches to abiogenesis investigate how self-replicating molecules, or their components, came into existence. [122], All known life forms share fundamental molecular mechanisms, reflecting their common descent; based on these observations, hypotheses on the origin of life attempt to find a mechanism explaining the formation of a universal common ancestor, from simple organic molecules via pre-cellular life to protocells and metabolism. [221] Hence, fossils range in age from the youngest at the start of the Holocene Epoch to the oldest from the Archaean Eon, up to 3.4 billion years old. One possibility for how life began is that genes originated first, followed by proteins;[125] the alternative being that proteins came first and then genes. Because living organisms are machines,[45] the Second Law applies to life as well. [232] The explanation given for the unusual speed of these reactions at such a low temperature is eutectic freezing. In particular, experiments by Butlerov (the formose reaction) showed that tetroses, pentoses, and hexoses are produced when formaldehyde is heated under basic conditions with divalent metal ions like calcium. [95][96][97] Evidence suggests that life on Earth has existed for at least 3.5 billion years,[98][99][100][101][102][103][104][105][106] with the oldest physical traces of life dating back 3.7 billion years;[107][108][109] however, some theories, such as the Late Heavy Bombardment theory, suggest that life on Earth may have started even earlier, as early as 4.1–4.4 billion years ago,[98][99][100][101][102] and the chemistry leading to life may have begun shortly after the Big Bang, 13.8 billion years ago, during an epoch when the universe was only 10–17 million years old.

Research at the University of Glasgow, in Scotland, has given rise to the theory that life on Earth may have evolved in clay.

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. An MIT physicist has proposed the provocative idea that life exists because the law of increasing entropy drives matter to acquire lifelike physical properties. Somewhere in this cycle work must be done, which means that free energy must be expended. [236][237][238], A research project completed in 2015 by John Sutherland and others found that a network of reactions beginning with hydrogen cyanide and hydrogen sulfide, in streams of water irradiated by UV light, could produce the chemical components of proteins and lipids, as well as those of RNA,[239][240] while not producing a wide range of other compounds. Those researchers think that "the prolonged pressure of genome and particle size reduction eventually reduced virocells into modern viruses (identified by the complete loss of cellular makeup), meanwhile other coexisting cellular lineages diversified into modern cells. Only time and further research can truly tell if there really is any energy in these claims. In this view, everything in the material universe has both matter and form, and the form of a living thing is its soul (Greek psyche, Latin anima). Others, such as Eugene Shakhnovich, a professor of chemistry, chemical biology and biophysics at Harvard University, are not convinced. [196] In 2010, another team also detected PAHs, along with fullerenes, in nebulae.
M.D> Brasier (2012), "Secret Chambers: The Inside Story of Cells and Complex Life" (Oxford Uni Press), p.298, Ward, Peter & Kirschvink, Joe, op cit, p. 42, For a deeper integrative version of this hypothesis, see in particular, CS1 maint: DOI inactive as of October 2020 (. The individual members of a colony are capable of surviving on their own, whereas the members of a true multi-cellular organism have developed specializations, making them dependent on the remainder of the organism for survival. [47] No one has yet synthesized a "protocell" using simple components with the necessary properties of life (the so-called "bottom-up-approach"). “We can show very simply from the formula that the more likely evolutionary outcomes are going to be the ones that absorbed and dissipated more energy from the environment’s external drives on the way to getting there,” he said. 3.5 Gao hot spring deposits", "SIMS analyses of the oldest known assemblage of microfossils document their taxon-correlated carbon isotope compositions", "Oldest fossils ever found show life on Earth began before 3.5 billion years ago", "Earliest evidence of life on Earth found", "Canadian bacteria-like fossils called oldest evidence of life", "Researchers uncover 'direct evidence' of life on Earth 4 billion years ago", "Cavitation-Induced Synthesis of Biogenic Molecules on Primordial Earth", "Microscopic dissipative structuring and proliferation at the origin of life", "Making Sense of the Chemistry That Led to Life on Earth", "When Did Life Likely Emerge on Earth in an RNA‐First Process? [101], Clark has suggested that homochirality may have started in outer space, as the studies of the amino acids on the Murchison meteorite showed that L-alanine is more than twice as frequent as its D form, and L-glutamic acid was more than three times prevalent than its D counterpart. Others have argued that a "top-down approach" is more feasible, starting with simple forms of current life. Life does not violate the second law of thermodynamics, but until recently, physicists were unable to use thermodynamics to explain why it should arise in the first place. Cell signaling coordinates cellular activities, and hence governs the basic functions of multicellular organisms. Other examples include sunlight and electrical discharges (lightning), among others.

For non-scientific views on the origins of life, see, Thermodynamics, self-organization, and information: Physics, Thermodynamics principles: Energy and entropy, Selforganization by dissipative structures, Current life, the result of abiogenesis: biology. A sequence of amino acids is assembled and joined together based upon gene expression of the cell's nucleic acid.


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