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12/01/2010 · What is the first step in photosynthesis
About the time that the continents began to grow and began, Earth produced its first known glaciers, between 3.0 and 2.9 bya, although the full extent is unknown. It might have been an ice age or merely some mountain glaciation. The , and numerous competing hypotheses try to explain what produced them. Because the evidence is relatively thin, there is also controversy about the extent of Earth's ice ages. About 2.5 bya, the Sun was probably a little smaller and only about as bright as it is today, and Earth would have been a block of ice if not for the atmosphere’s carbon dioxide and methane that absorbed electromagnetic radiation, particularly in the . But life may well have been involved, particularly oxygenic photosynthesis, and it was almost certainly involved in Earth's first great ice age, which may have been a episode, and some pertinent dynamics follow.
In summary, today’s orthodox late-Proterozoic hypothesis is that the complex dynamics of a supercontinent breakup somehow triggered . The global glaciation was reversed by runaway effects primarily related to an immense increase in atmospheric carbon dioxide. During the events, oceanic life would have been delivered vast amounts of continental nutrients scoured from the rocks by glaciers, and the hot conditions would have combined to create a global explosion of photosynthetic life. A billion years of relative equilibrium between prokaryotes and eukaryotes was ultimately shattered, and oxygen levels began rising during the Cryogenian and Ediacaran periods toward modern levels. Largely sterilized oceans, which began to be oxygenated at depth for the first time, are now thought to have prepared the way for what came next: the rise of complex life.
the first step in the beginning of photosynthesis ..
But the African Oligocene event of most interest to most humans was African primate evolution. By the Eocene’s end, primates were extinct in Europe and North America, and largely gone in Asia. Africa became the Oligocene's refuge for primates as they lived in the remaining rainforest. The first animals that evolved in the late Eocene, and what appears to be a appeared in Africa at the Oligocene’s beginning, about 35-33 mya. But ancestral to that creature was one that also led to those that migrated to South America, probably via vegetation rafts (with perhaps a land bridge helping), around the same time. Those South American monkeys are known as today and they evolved in isolation for more than 30 million years. For those that stayed behind in Africa, first appeared around the same time as those New World monkeys migrated; they diverged from . Scientists today think that somewhere between about 35 mya and 29 mya the splits between those three lineages happened. Old World and New World monkeys have not changed much in the intervening years, but apes sure have.
To revisit the Neanderthal split from about 500 kya, stayed in West Asia and Africa. When evidence of came to light, some scientists placed the beginning of the at about 500 kya. Stone tools have recently been dated using , which works for stone tools heated by fires, and using . That method measures water absorption into the surface of obsidian tools. For dating artifacts before the appearance of behaviorally modern humans about 70-50 kya, will not work, but successful. Neanderthals dominated Europe and today’s Middle East while home was Africa, and they also ranged to Europe and West Asia. Whether existed for only a half-million years or a million is controversial today, but what is not very controversial is that it is probably the direct ancestor of both Neanderthals and , and the first members of our species appeared in Africa about 200 kya. There is evidence that other descendants of may have existed, and . It also could have been a Neanderthal descendant. As with the discovery of the “” of Flores Island, it will not be surprising if scientists find more species that branched off of those early human and protohuman lines and died out when behaviorally modern humans spread across Africa and Eurasia.
What is the first step in the beginning of photosynthesis ..
Trees first appeared during a plant diversity crisis, and the arrival of seed plants and ferns ended the dominance of the first trees, so the plant crises may have been more about evolutionary experiments than environmental conditions, although a carbon dioxide crash and ice age conditions would have impacted photosynthesizers. The that gave rise to trees and seed plants largely went extinct at the Devonian’s end. But what might have been the most dramatic extinction, as far as humans are concerned, was the impact on land vertebrates. During the about 20% of all families, 50% of all genera, and 70% of all species disappeared forever.
From about 32 kya to 22 kya, prevailed in Europe. That culture produced the and art such as the . By 20 kya, . But as far as human expansion is concerned, the Gravettian (and related cultures) are most notorious as mammoth hunters extraordinaire for those that lived on the near the ice sheets. To , they could not swim to Sahul, but flourished everywhere else they could get to. At , they were the ultimate hunter-gatherer kill. Also, near the ice sheets, meat could be stored in the ground. Cro-Magnons did just that, and that “freezer” full of meat led to the first seasonally sedentary humans. It long predated the Domestication Revolution when people could be sedentary year-round, but while the megafauna lasted, the first signs of what came later appeared as Cro-Magnons created villages around frozen mammoth meat. Gravettians hunted along migration routes and set traps and ambushes for mammoths. For thousands of years, mammoths were the primary focus of Gravettian hunters, and many scientists believe that humans at least . Gravettians probably used the bow and arrow, and using poisoned arrows on mammoths would have been child’s play, not a hazardous undertaking. They also tended to focus on the easy meat: the young, relatively defenseless, tender mammoths. Killing the offspring alone would have driven the slowly reproducing mammoths to extinction, and as the interglacial period began around 15 kya, there would have been new pressures on mammoths. One of them was that fewer mammoths meant that they were not terraforming their environments like they used to, and the warming climate probably reduced their range. For a mammoth facing humans, there was literally no place to hide (except maybe in the living room), and there is little reason to think that hunters would have eased up when mammoth numbers dwindled. If anything, their efforts would have to get the last ones, as they competed and fought over the final mammoths. In one lifetime or even several, the changes would have been barely noticeable, if at all. There was simply no way out for mammoths, and they went extinct south of the European ice sheets under the ministrations of Cro-Magnon hunters. More evidence of their fate is some mammoths surviving in refugia: islands where humans did not arrive until thousands of years later. mammoths survived on in the chain off of Alaska until less than six kya, and went extinct when humans arrived. Several hundred apparently full-sized mammoths survived on near Siberia and went extinct less than five kya, when humans arrived. In today's France and Spain, Gravettians also semi-settled along the migration routes of reindeer and red deer. From Spain across Europe, into today's Russia, Gravettians hunted migrating herds, and not only the mammoth was driven to extinction, but also the wooly rhino, the Irish elk, the musk ox, and steppe bison were driven to extinction as the ice sheets retreated. Neanderthals had been ambush hunting in similar fashion, and those animals, like the African megafauna, grew wary of humans, and killing those animals probably took planning and guile.
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What happens in the first step of Photosynthesis
The high oxygen levels may have turned pyrite on the continents into acid, which increased erosion, flooded essential nutrients, particularly phosphorus, into the oceans, and would have facilitated a huge bloom in the oceans. But this also happened in the midst of Earth's first ice age, so increased glacial erosion may have been primarily responsible, as we will see with a . The two largest carbon-isotope excursions () in Earth's history are related to ice ages. The first was a positive excursion (more carbon-13 than expected), and the second was negative. Scientists are still trying to determine what caused them. Beginning a little less than 2.3 bya and lasting for more than 200 million years is the Lomagundi excursion, in which there was great carbon burial. When the Lomagundi excursion finished, oxygen levels seem to have crashed back down to almost nothing and may have stayed that way for 200 million years, before rebounding to a few percent, at most, of Earth's atmosphere, and it stayed around that low level for more than a billion years.
24/02/2014 · What is the first step of photosynthesis
As with other early life processes, the first photosynthetic process was different from today’s, but the important result – capturing sunlight to power biological processes – was the same. The scientific consensus today is that a respiration cycle was modified, and a in a was used for capturing sunlight. Intermediate stages have been hypothesized, including the cytochrome using a pigment to create a shield to absorb ultraviolet light, or that the pigment was part of an infrared sensor (for locating volcanic vents). But whatever the case was, the conversion of a respiration system into a photosynthetic system is considered to have only happened , and all photosynthesizers descended from that original innovation.
What happens in each step of photosynthesis? - Quora
Going back to the beginnings of the to how the to the , what Marx called separating the workers from the means of production had to be performed first so that the ownership class could form. With the workers put in their place, then the “owners” could create instruments of ownership and trade them. Thus began stock markets. Similar to how , when stock markets formed, owners became divorced from operations. In corporate America, for instance, there are theoretical governance mechanisms such as boards of directors and company officers that answer to the shareholders, but the relationship is often more theoretical than actual, and “cooking the books” to make management look good and inflate the stock price is as old as corporations. Dealing with that aspect of corporations is largely what I do to make a living. I have lived through several major financial scandals in my career, and they .
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