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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.
A careful estimate as of 2013 determined that humanity has reduced Earth’s plant-based biomass by more than a third since the beginnings of agriculture. Humanity certainly could not have industrialized by using wood. Arguments making the case that deforestation was not why coal was adopted in England are shaky and also irrelevant to the fact that England could not have industrialized with wood. Iron operations regularly shut down during England’s early industrial history due to wood shortages. The economics of coal were evident to even imperial Romans, but nobody would use coal if they could avoid it. Some until the late 19th century. But using sunlight energy captured during the tree’s life could not compete for long with mining ancient sunlight trapped in coal that was collected over tens of millions of years, even if nobody initially knew how coal was formed. Even today, the British Isles’ grassy hills provide austere evidence of the rampant deforestation that those lands have yet to recover from. That the British Isles have any woods at all is a testament to using fossil fuels to power the Industrial Revolution.
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Around the end of that , another unique event transpired with enormous portent for life’s journey on Earth: one microbe enveloped another, and both lived. Today's prevailing hypothesis is that an archaean enveloped a bacterium, either by predation or colonization, and they entered into a . Today’s leading hypothesis, , is that the archaean consumed hydrogen and the bacterium produced hydrogen, which formed the basis for their symbiosis. That unique event transpired around two bya and led to complex life on Earth. That enveloped bacterium was the parent of all on Earth today, which are the primary energy-generation centers in all animals. About 10% of the human body’s weight is mitochondria. If not for the red of and the in skin, humans would look purple, which is the mitochondria’s color. That purple color is probably because the original enveloped bacterium that led to the first mitochondrion was .
About 2.7 bya, dissolved iron in anoxic oceans seems to have begun reacting with oxygen at the surface, generated by cyanobacteria. The dissolved iron was oxidized from a soluble form to an insoluble one, which then precipitated out of the oceans in those vivid red (the color of rust) layers that we see today and are called ("BIFs"), which became an oxygen sink and kept atmospheric oxygen low. The GOE is widely accepted to have created almost all of the BIFs, but it is not the only BIF-formation hypothesis and there is a great deal of controversy, but life processes are generally considered to be primarily responsible for forming the BIFs. Most iron in the crust is bound in silicates and carbonates, and it takes a great deal of energy to extract the iron from those minerals; the oxides that comprise BIFs are much less energy-intensive to refine, as the iron is so concentrated. Far less ore needs to be melted to get an equivalent amount of iron. BIFs are the source of virtually all iron ore that humans have mined. Life processes almost certainly performed the initial work of refining iron, and humans easily finished the job billions of years later. Copper was not refined by life processes, and copper ore takes twice as much energy to refine as iron ore does.
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The Panthalassic’s currents were slow and lazy, and the deep-water oxygenation of today’s oceans would have been quite different, and perhaps largely . Also, when form, the falls as the oceanic basin expands, and the late Permian's sea levels are thought to be among the lowest in the . The many shallow seas of complex life’s earlier periods also disappeared with the formation of Pangaea (nearly 90% of the continental shelves became exposed), which were the abode of most marine life. That new land exposed the swamps and deltas formed in the Carboniferous, and the oxidation of those carbonaceous deposits drew down atmospheric oxygen and increased carbon dioxide. The merging of continents also results in mountain-building and volcanism.
When the total continental land mass was small or combined into a supercontinent, there was no land to divert that diffusion of warm water toward the poles, which results in currents. During those times, the global ocean became one big, calm lake, with no currents of significance. Those oceans are called today, and they would have been anoxic; the oxygenated surface waters would not have been drawn by currents to the ocean floor, and the oceans were certainly anoxic before the GOE. The interplay of those can be incredibly complex and lead to the multitude of hypotheses posited to explain those ancient events, but a leading hypothesis today is that a combination of factors, including supercontinents, variations in volcanic output, Canfield Oceans, and ice ages prevented life from gaining ecosystem dominance until the waning of the second Snowball Earth event, which was the greatest series of glaciations that Earth has yet experienced. It is known today as the , which ended about 635 mya. The study of the Cryogenian Period, which is the subject of , resulted in the term “.”
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Although our species, (named if we consider that Neanderthals and an are subspecies of but I will use in this essay to denote today’s humans), is the only survivor of the past several million years of human-line evolution, many of our cousins and ancestors were recognizably human. When did language begin, especially spoken language? Language certainly predated the appearance of . All great apes readily learn sign language, and even when monkeys chatter, the , and there is plenty of evidence that great ape vocalizations can . The and their corvid cousins can be hard to believe; they can solve some problems better than great apes can, and birds do not have a neocortex, but seems to function like the neocortex does. Becoming that began to . If fossils are sufficiently preserved, important anatomical features can provide key evidence for human abilities and behaviors. Turkana Boy, for instance, had his inner ear, which is responsible for balance, preserved well enough so that it provided more evidence that he did not spend time in trees (it is larger in primates that regularly climb). Similarly, the , which succeeded , apparently enabled keener hearing than its predecessors were capable of, and may have reflected the beginnings of spoken language. There is strong evidence that . As with many other human traits, the potential for language seems to have existed with monkeys (), and it kept developing more sophistication over vast stretches of time, and structural and cognitive changes interacted as human language developed into today’s version.
Compare & Contrast Essay: The Role of Women in Ancient Athens
Two major events happened soon after appeared, and their sequence seems to support the Cooking Hypotheses. The first of which was the migration of from Africa ; they spread to and by 1.8 mya (perhaps 1.6 mya in the case of Java), and . It was the , and may have become the first multi-continental member of the human line, and certainly the first widespread one. Favorable climates and a lower Himalaya range and Tibetan Plateau may have encouraged that migration. Unlike Miocene apes that began to migrate from Africa 16.5 mya, there was no unbroken forest to sustain journey to East Asia. Those migrants would have to sleep on the ground for much of the journey and were not adapted for sleeping in trees, . From today’s viewpoint, it may seem that they were adventurers, but as will also become obvious with the spread of , in one individual’s lifetime, there was probably only modest movement, expanding into the next uninhabited valley or two. Such an expansion happened one valley at a time, one generation at a time, to make it across a continent in a few thousand years for those that could adapt to changing biomes. Migrating at the same latitude would not have presented great climatic issues. As those migrations happened during the ice age, they were along southern Eurasia. There is no evidence yet that ever made it to Australia, probably because of the ocean crossing required for passage.
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