what are theories of origin of life on earth?
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We know from fossil stromatolites that life on earth began more than 3 billion years ago.
There are a number of competing ideas on how life might have begun. There are no concrete answers, however. It is a complex problem. "Panspermia" suggests life was seeded on earth from elsewhere in the galaxy--perhaps drifting down on board some meteorite with a slow trajectory. We have found meteorites from arctic ice to wheatfields. This simply pushes back the origin of life question, however.
Another idea suggests that before our DNA based world there was a simpler RNA based world. Self replicating RNA would have been replaced by self replicating DNA when the latter mutated into existence. Although we have synthesized self replicating RNA through natural means in laboratories, that is still a big step from DNA and cells, and no clear pathway has yet been discerned for cellular abiogenesis.
A third hypothesis suggests there may be simpler self replicating organic molecules which served as percursors to self replicating DNA. You can find an article about this in a recent edition of Scientific American.
A popular hypothesis (none of these are really fleshed out as full fledged "theories") is that life began near deep ocean hydrothermal vents. We find that amino acids occur naturally in such environments--just as they do in the Miller/Urey experiments, and even out in space (back to "panspermia.") Amino acids to archaeobacteria is still such a huge gulf, however.
Many biologists suspect there is some as yet unknown phenomenon that makes the origin of life next to inevitable given proper environmental conditions. Precisely what this might be remains unclear at this time. The reason this is suspected is because life started on this planet very early, when conditions for its existence as we find it were not particularly favorable.
One problem is that biologists continue to lack a particularly good, simple definition of "life." Are viruses alive? Fire consumes and grows, but most folks reject the notion it is alive.
There are a number of competing ideas on how life might have begun. There are no concrete answers, however. It is a complex problem. "Panspermia" suggests life was seeded on earth from elsewhere in the galaxy--perhaps drifting down on board some meteorite with a slow trajectory. We have found meteorites from arctic ice to wheatfields. This simply pushes back the origin of life question, however.
Another idea suggests that before our DNA based world there was a simpler RNA based world. Self replicating RNA would have been replaced by self replicating DNA when the latter mutated into existence. Although we have synthesized self replicating RNA through natural means in laboratories, that is still a big step from DNA and cells, and no clear pathway has yet been discerned for cellular abiogenesis.
A third hypothesis suggests there may be simpler self replicating organic molecules which served as percursors to self replicating DNA. You can find an article about this in a recent edition of Scientific American.
A popular hypothesis (none of these are really fleshed out as full fledged "theories") is that life began near deep ocean hydrothermal vents. We find that amino acids occur naturally in such environments--just as they do in the Miller/Urey experiments, and even out in space (back to "panspermia.") Amino acids to archaeobacteria is still such a huge gulf, however.
Many biologists suspect there is some as yet unknown phenomenon that makes the origin of life next to inevitable given proper environmental conditions. Precisely what this might be remains unclear at this time. The reason this is suspected is because life started on this planet very early, when conditions for its existence as we find it were not particularly favorable.
One problem is that biologists continue to lack a particularly good, simple definition of "life." Are viruses alive? Fire consumes and grows, but most folks reject the notion it is alive.
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Answer:
✔Theory of special creation:
It states that God created life by his divine act of creation.
✔Theory of Panspermia/Cosmozoic:
It stated that the spores or panspermia cane from outer space and developed into living forms.
✔Theory of spontaneous generation:
It stated that life originated from decaying and rotting matter like straw, mud, etc.
✔Theory of chemical evolution or Oparin-Haldane theory:
Life originated from pre-existing non-living organic molecules and that formation of life was preceded by chemical evolution.
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