Photosynthetic Fractionation of Carbon Isotopes

Farquhar GD, Ehleringer JR, Hubick KT (1989) Carbon isotope discrimination and photosynthesis. Annual Review of Plant Physiology and Plant Molecular Biology 40, 503–537.

Roeske CA and O’Leary MH (1985) Carbon isotope ..

Plants discriminate carbon isotopes during photosynthesis

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Roeske CA, O’Leary MH (1985) Carbon isotope effect on carboxylation of ribulose bisphosphate catalyzed by ribulosebisphosphate carboxylase from Biochemistry 24, 1603–1607.

Plants fractionate carbon isotopes during photosynthesis

Roeske CA, O’Leary MH (1984) Carbon isotope effects on the enzyme-catalyzed carboxylation of ribulose bisphosphate. Biochemistry 23, 6275–6284.

O'Leary MH: Carbon isotopes in photosynthesis.

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Guy RD, Fogel ML, Berry JA (1993) Photosynthetic fractionation of the stable isotopes of oxygen and carbon. Plant Physiology 101, 37–47.

Photosynthetic fractionation of carbon isotopes

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.

H., Carbon isotopes in photosynthesis

When cyanobacteria began using water in photosynthesis, carbon was captured and oxygen released, which began the oxygenation of Earth's atmosphere. But the process may have not always been a story of continually increasing atmospheric oxygen. There may have been wild swings. Although the process is indirect, oxygen levels are influenced by the balance of carbon and other elements being buried in ocean sediments. If carbon is buried in sediments faster than it is introduced to the atmosphere, oxygen levels will increase. is comprised of iron and sulfur, but in the presence of oxygen, pyrite's iron combines with oxygen (and becomes iron oxide, also known as rust) and the sulfur forms sulfuric acid. Pyrite burial may have acted as the dominant oxygen source before carbon burial did. There is sulfur isotope evidence that Earth had almost no atmospheric oxygen before 2.5 bya.

Carbon Isotopes in Photosynthesis, by Marion H

Roeske CA, O’Leary MH (1984) Carbon isotope effects on the enzyme catalyzed carboxylation of ribulose bisphosphate. Biochemistry 23, 6275–6284.