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To serve as a characteristic example of.
Anthropologists and primate researchers , but relatively recent scientific findings have disproven that notion. , and it is more sophisticated with great apes. It took a few million years after the human/chimp split for our ancestors to learn to , and that culture then spread widely in Africa. The , , and were probably all closely related and at least partly interdependent, but little seemed to change . Then the and possessed a larger brain, and new tools and behaviors are evident . The timeframes continually shrank between major events in the human journey. Only 200 thousand years later, and , and new behaviors are in evidence. Only 100 thousand years after that, anatomically modern humans appeared. Only 30 thousand years after that, about 170 kya, , probably due to necessity, where life once again was eked out on the margins, and those humans may have decorated their bodies. About 100 kya, innovation seems to have accelerated again, and by 75-60 kya there is evidence of . Needles and perhaps even arrowheads first appeared about 60 kya. There is no doubt among scientists that members of made those advances, and their artifacts provided evidence of increasing cultural and technical sophistication, which soon left Neanderthals and all other land animals far behind. About 75-70 kya, a , and there is controversy today whether that eruption was partly responsible for the that passed through not long afterward. What became today’s humanity seems to have nearly gone extinct at that bottleneck.
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There have been other proximate causes of our current ice age, beginning with around 40 mya, and when the land bridge formed between the Americas around three mya , and are responsible for the "wobble" of advancing and retreating ice sheets in the Northern Hemisphere during this ice age. There is always the battle of the hypotheses in scientific circles, but the nearly universal consensus is that greenhouse gases, oceanic currents (with a land mass at the South Pole, and the landlocked North Pole), and Milankovitch cycle dynamics, in that ranking of importance, have caused the current ice age. Until the rise of humanity, the primary carbon dioxide input into the carbon cycle was via volcanism, which is related to tectonic plate movements, and plate movements also affected oceanic currents. Scientists are continually surprised by the dynamics and extent of Global Warming, and usually an unpleasant surprise, such as the findings published in 2014 which show that the Antarctic ice sheets are melting faster than expected, and in unexpected ways, and the Greenland ice sheet is also yielding alarming surprises.
, including the salt retention hypothesis
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Cestoidea () A class of parasitic worms (Platelminthes) of which the tapeworms are the most common examples. The body is flattened, and usually but not always long, and composed of numerous joints or segments, each of which may contain a complete set of male and female reproductive organs. They have neither mouth nor intestine. See Tapeworm.
The ability to weigh various isotopes, at increasing levels of precision, with mass spectrometers has provided a gold mine of data. Scientists are continually inventing new methods and ways to use them, new questions are asked and answered, and some examples of methods and findings follow.
Energy and the Human Journey: Where We Have Been; …
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Remontant () Rising again; -- applied to a class of roses which bloom more than once in a season; the hybrid perpetual roses, of which the Jacqueminot is a well-known example.
In the oceans, the Carboniferous is called the Golden Age of Sharks, and ray-finned fish arose to a ubiquity that they have yet to fully relinquish. Ray-finned fish probably prevailed because of their high energy efficiency. Their skeletons and scales were lighter than those of armored and lobe-finned fish, and their increasingly sophisticated and lightweight fins, their efficient tailfin method of propulsion, changes in their skulls, jaws, and new ways to use their lightweight and versatile equipment accompanied and probably led to the rise and subsequent success of ray-finned fish in the Carboniferous and afterward. , which are amoebic protists, rose to prominence for the first time in the Carboniferous. Reefs began to recover, although they did not recover to pre-Devonian conditions; those vast Devonian reefs have not been seen again. did not appear until the . Trilobites steadily declined and nautiloids familiar today, and straight shells became rare. The first , which were ancestral to squids and octopi, first appeared in the early Carboniferous, but some Devonian specimens might qualify. Ammonoids flourished once again, after barely surviving the Devonian Extinction. This essay is only focusing on certain prominent clades, and there are many and . The early Carboniferous, for example, is called the Golden Age of , which are a kind of , which is a phylum that includes starfish. The crinoids had their golden age when the fish that fed on them disappeared in the end-Devonian extinction. Earth’s ecosystems are vastly richer entities than this essay, or essay, can depict.
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Make It Stick the Science of Successful Learning | …
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.
Kingdoms of the Barbarians - Celtic Tribes
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 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.
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