Top 10 Theories on Beginning of Life on Earth
The details of the origin of life are unknown, but the basic principles have been established. There are basically two schools of thought which are further divided into many about the origin of life. One suggests that organic components arrived on Earth from space, while the other argues that they originated on Earth.
Panspermia is the hypothesis that life exists throughout the Universe, distributed by meteoroids, asteroids and planetoids. Panspermia proposes that life that can survive the effects of space, such as extremophile bacteria, become trapped in debris that is ejected into space after collisions between planets that harbor life and Small Solar System Bodies (SSSB). Bacteria may travel dormant for an extended amount of time before colliding randomly with other planets or intermingling with protoplanetary disks. If met with ideal conditions on a new planets’ surfaces, the bacteria become active and the process of evolution begins.
Recent probes inside comets show it is overwhelmingly likely that life began in space, according to a new paper by Cardiff University scientists.
In natural science, abiogenesis or biopoesis is the study of how biological life arises from inorganic matter through natural processes, and the method by which life on Earth arose. Most amino acids, often called “the building blocks of life”, can form via natural chemical reactions unrelated to life, as demonstrated in the Miller–Urey experiment and similar experiments that involved simulating some of the conditions of the early Earth in a laboratory. In all living things, these amino acids are organized into proteins, and the construction of these proteins is mediated by nucleic acids, that are themselves synthesized through biochemical pathways catalysed by proteins. Which of these organic molecules first arose and how they formed the first life is the focus of abiogenesis.
Cosmogeny, is any theory concerning the coming into existence or origin of the universe, or about how reality came to be. In the specialized context of space science and astronomy, the term refers to theories of creation of (and study of) the Solar System. Attempts to create a naturalistic cosmogony are subject to two separate limitations. One is based in the philosophy of science and the epistemological constraints of science itself, especially with regards to whether scientific inquiry can ask questions of “why” the universe exists. Another more pragmatic problem is that there is no physical model that can explain the earliest moments of the universe’s existence because of a lack of a testable theory of quantum gravity, although string theorists and researchers in loop quantum cosmology believe they have the formulas to describe it within their field equations.
The endosymbiotic theory was first articulated by the Russian botanist Konstantin Mereschkowski in 1905. According to this theory, certain organelles originated as free-living bacteria that were taken inside another cell as endosymbionts. Mitochondria developed from proteobacteria (in particular, Rickettsiales or close relatives) and chloroplasts from cyanobacteria. It suggests that multiple forms of bacteria entered into symbiotic relationship to form the eukaryotic cell. The horizontal transfer of genetic material between bacteria promotes such symbiotic relationships, and thus many separate organisms may have contributed to building what has been recognised as the Last Universal Common Ancestor (LUCA) of modern organisms.
6. Spontaneous Generation
Until the early 19th century, people generally believed in the ongoing spontaneous generation of certain forms of life from non-living matter. This was paired with the belief in heterogenesis, e.g. that one form of life derived from a different form (e.g. bees from flowers). Classical notions of spontaneous generation, held that certain complex, living organisms are generated by decaying organic substances. According to Aristotle it was a readily observable truth that aphids arise from the dew which falls on plants, flies from putrid matter, mice from dirty hay, crocodiles from rotting logs at the bottom of bodies of water, and so on. Spontaneous generation or Equivocal generation is considered obsolete by many, regarding the origin of life from inanimate matter, which held that this process was a commonplace and everyday occurrence, as distinguished from univocal generation, or reproduction from parent(s). The theory was synthesized by Aristotle, who compiled and expanded the work of prior natural philosophers and the various ancient explanations of the appearance of organisms; it held sway for two millennia. It is generally accepted to have been ultimately disproven in the 19th Century by the experiments of Louis Pasteur. The disproof of ongoing spontaneous generation is no longer controversial, now that the life cycles of various life forms have been well documented. However, the question of biopoesis or abiogenesis, how living things originally arose from non-living material, remains relevant today
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