Infernity
Please continue. How *exactly* do non-living materials come to life?
-Stephen
Stephen,
If you want to have the short precise explanation you'll have to wait till the holiday here ends (16th) so I can take that thingie I have somewhere in my locker.
There were no oceans and no oxygen in the atmosphere. It was bombarded by planetoids and other material left over from the formation of the solar system. This bombardment, combined with heat from radioactive breakdown, residual heat, and heat from the pressure of contraction, caused the planet at this stage to be fully molten.
Heavier elements sank to the center while lighter ones rose to the surface, producing Earth's various layers. Earth's early atmosphere would have comprised surrounding material from the solar nebula, especially light gases such as hydrogen and helium, but the solar wind and Earth's own heat would have driven off this atmosphere.
This changed when Earth was about 40% its present radius, and gravitational attraction allowed the retention of an atmosphere which included water. Temperatures plummeted and the crust of the planet was accumulated on a solid surface, with areas melted by large impacts on the scale of decades to hundreds of years between impact. Large impacts would have caused localized melting and partial differentiation, with some lighter elements on the surface or released to the moist atmosphere.
The surface cooled quickly, forming the solid crust within 150 million years. From 4 to 3.8 billion years ago, Earth underwent a period of heavy asteroidal bombardment. Steam escaped from the crust while more gases were released by volcanoes, completing the second atmosphere. Additional water was imported by bolide collisions, probably from asteroids ejected from the outer asteroid belt under the influence of Jupiter's gravity. The planet cooled. Clouds formed. Rain gave rise to the oceans within 750 million years. The new atmosphere probably contained ammonia, methane, water vapor, carbon dioxide, and nitrogen, as well as smaller amounts of other gases. Any free oxygen would have been bound by hydrogen or minerals on the surface. Volcanic activity was intense and, without an ozone layer to hinder its entry, ultraviolet radiation flooded the surface.
It is likely that the initial cells were all heterotrophs, using surrounding organic molecules (including those from other cells) as raw material and an energy source. As the food supply diminished, a new strategy evolved in some cells. Instead of relying on the diminishing amounts of free-existing organic molecules, these cells adopted sunlight as an energy source.
Estimates vary, but by about 3 billion years ago, something similar to modern photosynthesis had probably developed. This made the sun’s energy available not only to autotrophs but also to the heterotrophs that consumed them. Photosynthesis used the plentiful carbon dioxide and water as raw materials and, with the energy of sunlight, produced energy-rich organic molecules (carbohydrates).
Moreover, oxygen was produced as a waste product of photosynthesis. At first it became bound up with limestone, iron, and other minerals. There is substantial proof of this in iron-oxide rich layers in geological strata that correspond with this time period. The oceans would have turned to a green color while oxygen was reacting with minerals. When the reactions stopped, oxygen could finally enter the atmosphere. Though each cell only produced a minute amount of oxygen, the combined metabolism of many cells over a vast period of time transformed Earth’s atmosphere to its current state.This, then, is Earth’s third atmosphere. Some of the oxygen was stimulated by incoming ultraviolet radiation to form ozone, which collected in a layer near the upper part of the atmosphere. The ozone layer absorbed, and still absorbs, a significant amount of the ultraviolet radiation that once had passed through the atmosphere. It allowed cells to colonize the surface of the ocean and ultimately the landwithout the ozone layer, ultraviolet radiation bombarding the surface would have caused unsustainable levels of mutation in exposed cells. Besides making large amounts of energy available to life-forms and blocking ultraviolet radiation, the effects of photosynthesis had a third, major, and world-changing impact. Oxygen was toxic; probably much life on Earth died out as its levels rose. Resistant forms survived and thrived, and some developed the ability to use oxygen to enhance their metabolism and derive more energy from the same food.
Modern taxonomy classifies life into three domains. The time of the origin of these domains are speculative. The Bacteria domain probably first split off from the other forms of life (sometimes called Neomura), but this supposition is controversial. Soon after this, by 2 billion years ago the Neomura split into the Archaea and the Eukarya. Eukaryotic cells (Eukarya) are larger and more complex than prokaryotic cells (Bacteria and Archaea), and the origin of that complexity is only now coming to light. Around this time period a bacterial cell related to today’s Rickettsia entered a larger prokaryotic cell. Perhaps the large cell attempted to ingest the smaller one but failed (maybe due to the evolution of prey defenses). Perhaps the smaller cell attempted to parasitize the larger one. In any case, the smaller cell survived inside the larger cell. Using oxygen, it was able to metabolize the larger cell’s waste products and derive more energy. Some of this surplus energy was returned to the host. The smaller cell replicated inside the larger one, and soon a stable symbiotic relationship developed. Over time the host cell acquired some of the genes of the smaller cells, and the two kinds became dependent on each other: the larger cell could not survive without the energy produced by the smaller ones, and these in turn could not survive without the raw materials provided by the larger cell. Symbiosis developed between the larger cell and the population of smaller cells inside it to the extent that they are considered to have become a single organism, the smaller cells being classified as organelles called mitochondria. A similar event took place with photosynthetic cyanobacteriaentering larger heterotrophic cells and becoming chloroplasts. Probably as a result of these changes, a line of cells capable of photosynthesis split off from the other eukaryotes some time before one billion years ago There were probably several such inclusion events, as the figure at right suggests. Besides the well-established endosymbiotic theory of the cellular origin of mitochondria and chloroplasts, it has been suggested that cells gave rise to peroxisomes, spirochetes gave rise to cilia and flagella, and that perhaps a DNA virus gave rise to the cell nucleus though none of these theories are generally accepted. During this period, the supercontinent Columbia is believed to have existed, probably from around 1.8 to 1.5 billion years ago it is the oldest hypothesized supercontinent.
Archaeans, bacteria, and eukaryotes continued to diversify and to become more sophisticated and better adapted to their environments. Each domain repeatedly split into multiple lineages, although little is known about the history of the archaea and bacteria. Around 1.1 billion years ago the supercontinent Rodinia was assembling. The plant, animal, and fungi lines had all split, though they still existed as solitary cells. Some of these lived in colonies, and gradually some division of labor began to take place; for instance, cells on the periphery might have started to assume different roles from those in the interior. Although the division between a colony with specialized cells and a multicellular organism is not always clear, around 1 billion years ago the first multicellular plants emerged, probably green algae. Possibly by around 900 million years ago true multicellularity had also evolved in animals. At first it probably somewhat resembled that of today’s sponges, where all cells were totipotent and a disrupted organism could reassemble itself. As the division of labor became more complete in all lines of multicellular organisms, cells became more specialized and more dependent on each other; isolated cells would die. Many scientists believe that a very severe ice age began around 770 million years ago, so severe that the surface of all the oceans completely froze (Snowball Earth). Eventually, after 20 million years, enough carbon dioxide escaped through volcanic outgassing; the resulting greenhouse effect raised global temperatures. By around the same time, 750 million years ago, Rodinia began to break up.
As we have already seen, the accumulation of oxygen in Earth’s atmosphere resulted in the formation of ozone, forming a layer that absorbed much of the sun’s ultraviolet radiation. As a result, unicellular organisms that reached land were less likely to die, and prokaryotes began to multiply and become better adapted to survival out of the water. Prokaryotes had likely colonized the land as early as 2.6 billion years ago, prior even to the origin of the eukaryotes. For a long time, the land remained barren of multicellular organisms. The supercontinent Pannotia formed around 600 million years ago and then broke apart a short 50 million years later. Fish, the earliest vertebrates, evolved in the oceans around 530 million years ago. A major extinction event occurred near the end of the Cambrian period, which ended 488 million years ago.
Several hundred million years ago, plants (probably resembling algae) and fungi started growing at the edges of the water, and then out of it. The oldest fossils of land fungi and plants date to 480–460 million years ago, though molecular evidence suggests the fungi may have colonized the land as early as 1000 million years ago and the plants 700 million years ago. Initially remaining close to the water’s edge, mutations and variations resulted in further colonization of this new environment. The timing of the first animals to leave the oceans is not precisely known: the oldest clear evidence is of arthropods on land around 450 million years ago, perhaps thriving and becoming better adapted due to the vast food source provided by the terrestrial plants. There is also some unconfirmed evidence that arthropods may have appeared on land as early as 530 million years ago. At the end of the Ordovician period, 440 million years ago, additional extinction events occurred, perhaps as a result of a concurrent ice age. Around 380 to 375 million years ago the first tetrapods evolved from the fish. It is thought that perhaps fins evolved to become limbs which allowed the first tetrapods to lift their heads out of the water to breathe air. This would let them survive in oxygen-poor water or pursue small prey in shallow water. They may have later ventured on land for brief periods. Eventually, some of them became so well adapted to terrestrial life that they spent their adult lives on land, although they hatched in the water and returned to lay their eggs. This was the origin of the amphibians. About 365 million years ago, another period of extinction occurred, perhaps as a result of global cooling. Plants evolved seeds, which dramatically accelerated their spread on land, around this time.
Some twenty million years later , the evolution of the amniotic egg allowed eggs to be laid on land, certainly a survival advantage for the tetrapod embryos. This resulted in the divergence of amniotes from amphibians. Another thirty million years saw the divergence of the synapsids (including mammals) from the sauropsids (including birds and non-avian, non-mammalian reptiles). Of course, other groups of organisms continued to evolve and lines diverged—in fish, insects, bacteria, and so on—but not as much is known of the details. 300 million years ago the most recent supercontinent formed, called Pangaea. The most severe extinction event to date took place 250 million years ago, at the boundary of the Permian and Triassic periods; 95% of life on Earth died out, possibly as a consequence of the Siberian Traps volcanic event. The discovery of a crater hidden under the East Antarctic Ice Sheet has risen up a new theory that a meteor caused the mass extinction and possibly began the breakup of the Gondwana supercontinent by creating the tectonic rift that pushed Australia northward. But life persevered, and around 230 million years ago dinosaurs split off from their reptilian ancestors. An extinction event between the Triassic and Jurassic periods 200 million years ago, spared many of the dinosaurs, and they soon became dominant among the vertebrates. Though some of the mammalian lines began to separate during this period, existing mammals were probably all small animals resembling shrews. By 180 million years ago,Pangaea broke up into Laurasia and Gondwana. The boundary between avian and non-avian dinosaurs is not clear, but Archaeopteryx, traditionally considered one of the first birds, lived around 150 million years ago. The earliest evidence for the angiosperms evolving flowers is during the Cretaceous period, some twenty million years later, Competition with birds drove many pterosaurs to extinction, and the dinosaurs were probably already in decline for various reasons when, 65 million years ago, a 10-kilometer meteorite likely struck Earth just off the Yucatán Peninsula, ejecting vast quantities of particulate matter and vapor into the air that occluded sunlight, inhibiting photosynthesis. Most large animals, including the non-avian dinosaurs, became extinct. Marking the end of the Cretaceous period and Mesozoic era. Thereafter, in the Paleocene epoch, mammals rapidly diversified, grew larger, and became the dominant vertebrates. Perhaps a couple million years later, the last common ancestor of the all primates lived. By the late Eocene epoch, 34 million years ago, some terrestrial mammals had returned to the oceans to become animals such as Basilosaurus which would later give rise to the dolphins and whales.
Apes have consciousness, that's proven. I don't need to tel you of man's evolution (I hope), although that's also here. ... :
http://en.wikipedia....istory_of_Earth A while ago, someone linked someone to
http://FuckingGoogleIt.com/ I suggest you to just "Fucking
WikiThat"..,
-Infernity
Edited by infernity, 07 October 2006 - 04:05 PM.
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