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Two phases of photosynthesis - PowerPoint PPT …
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.
Around when Harland first proposed a global ice age, a climate model developed by Russian climatologist concluded that if a Snowball Earth really happened, the runaway positive feedbacks would ensure that the planet would never thaw and become a permanent block of ice. For the next generation, that climate model made a Snowball Earth scenario seem impossible. In 1992, a professor, , that coined the term Snowball Earth. Kirschvink sketched a scenario in which the supercontinent near the equator reflected sunlight, as compared to tropical oceans that absorb it. Once the global temperature decline due to reflected sunlight began to grow polar ice, the ice would reflect even more sunlight and Earth’s surface would become even cooler. This could produce a runaway effect in which the ice sheets grew into the tropics and buried the supercontinent in ice. Kirschvink also proposed that the situation could become unstable. As the sea ice crept toward the equator, it would kill off all photosynthetic life and a buried supercontinent would no longer engage in . Those were two key ways that carbon was removed from the atmosphere in the day's , especially before the rise of land plants. Volcanism would have been the main way that carbon dioxide was introduced to the atmosphere (animal respiration also releases carbon dioxide, but this was before the eon of animals), and with two key dynamics for removing it suppressed by the ice, carbon dioxide would have increased in the atmosphere. The resultant greenhouse effect would have eventually melted the ice and runaway effects would have quickly turned Earth from an icehouse into a greenhouse. Kirschvink proposed the idea that Earth could vacillate between states.
The two phases of photosynthesis are light reaction and dark reaction
For this essay’s purposes, the most important ecological understanding is that the Sun provides all of earthly life’s energy, either (all except nuclear-powered electric lights driving photosynthesis in greenhouses, as that energy came from dead stars). Today’s hydrocarbon energy that powers our industrial world comes from captured sunlight. Exciting electrons with photon energy, then stripping off electrons and protons and using their electric potential to power biochemical reactions, is what makes Earth’s ecosystems possible. Too little energy, and reactions will not happen (such as ice ages, enzyme poisoning, the darkness of night, food shortages, and lack of key nutrients that support biological reactions), and too much (such as , ionizing radiation, temperatures too high for enzyme activity), and life is damaged or destroyed. The journey of life on Earth has primarily been about adapting to varying energy conditions and finding levels where life can survive. For the many hypotheses about those ancient events and what really happened, the answers are always primarily in energy terms, such as how it was obtained, how it was preserved, and how it was used. For life scientists, that is always the framework, and they devote themselves to discovering how the energy game was played.
But the most impressive dual-use innovation in mollusks is what cephalopods invented. Their gill pumps are quite muscular and . That . Jet propulsion is not an energy-efficient means of transportation, but the cephalopod’s ability to pass oxygen-bearing water over its gills is unmatched. Cephalopods can live in waters too hypoxic for fish to survive. In the coming Ordovician Period, cephalopods would be apex predators of marine biomes and would hold that distinction for a long time. Cephalopods are today’s ; the and it has the largest brain-to-body-size ratio of all invertebrates. It is thought that the skills needed for predation stimulated cephalopodan intelligence. Today, the is the only survivor of that lineage of Ordovician apex predators.
What are the two main stages in photosynthesis? | …
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.
Two primary events drove the first phase of the Ordovician-Silurian mass extinction: the ice age caused the sea level to drop drastically and the oceans became colder. When sea levels fell at least 50 meters, the cooling shallow seas receded from continental shelves and eliminated entire biomes. Many millions of years of “easy living” in warm, shallow seas were abruptly halted. Several groups were ravaged, beginning with the plankton that formed the food chain’s base. About 50% of brachiopod and trilobite genera went extinct in the first phase, and cool-water species filled the newly vacant niches. Bivalves were largely found in seashore communities, were scourged when the seas retreated, and lost more than half of their genera. Nautiloids were also hit hard, and about 70% of reef and coral genera went extinct. The retreating seas somehow triggered the extinctions, and whether it was due to simply being exposed to the air or changing and cooling currents, nutrient dispersal patterns, ocean chemistry, and other dynamics is still debated, and those extinction events are being subjected to intensive research in the early 21st century.
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The Discovery of Photosynthesis - Julian Rubin
Kirschvink noted that reappeared in the geological record during the possible Snowball Earth times, after vanishing about a billion years earlier. Kirschvink noted that iron cannot increase to levels where they would create BIFs if the global ocean was oxygenated. Kirschvink proposed that the sea ice not only killed the photosynthesizers, but it also separated the ocean from the atmosphere so that the global ocean became anoxic. Iron from volcanoes on the ocean floor would build up in solution during the , and during the greenhouse phase the oceans would become oxygenated and the iron would fall out in BIFs. Other geological evidence for the vacillating icehouse and greenhouse conditions was the formation of cap carbonates over the glacial till. It was a global phenomenon; wherever the Snowball Earth till was, cap carbonates were atop them. In geological circles, deposited during the past 100 million years are considered to be of tropical origin, so scientists think that the cap carbonates reflected a tropical environment. The fact of cap carbonates atop glacial till is one of the strongest pieces of evidence for the Snowball Earth hypothesis. Kirschvink finished his paper by noting that the eon of complex life came on the heels of the Snowball Earth, and scouring the oceans of life would have presented virgin oceans for the rapid spread of life in the greenhouse periods, and this could have initiated the evolutionary novelty that led to complex life.
Kids learn about the science of photosynthesis
The , like the prior , was more than one event and had more than one cause. The is what most people think about when mass extinctions are mentioned (as it was Hollywood-spectacular and ended one fascinating line of animals and paved the way for mammals to dominate), and it led to the existence of humans, but the Permian extinction was the Big One. Before the began lifting in the 1970s and 1980s, specialists generally thought that the Permian extinction only impacted the oceans and left terrestrial ecosystems unaffected. The picture has radically changed since the 1980s, and the terrestrial extinctions are now acknowledged as similarly catastrophic. The Permian extinction is Earth’s only mass extinction of insects, and although plants are not normally vulnerable to mass extinctions, land plants also barely survived the Permian extinction. But the extinction came in phases, and each may have had different causes. There is great ongoing controversy and research regarding the issues.
Glossary of Biological Terms ← BACK
Also, the formation of Pangaea ( regarding what processes ) may have led to the dynamics that broke it apart. The Hawaiian Islands are that began forming more than 80 mya, and is due to a hotspot bubbling up from Earth’s mantle. Although the is , a prominent hypothesis is that the formation of Pangaea plugged hotspots and prevented heat from venting from Earth’s core, which led to a swelling and fracturing Pangaea. Part of the evidence for that hypothesis was relatively sudden and widespread volcanism sprouting up around Pangaea, which followed a known fracture pattern around such crustal upwellings. The volcanism and resultant fracture lines formed today’s continents. As can be seen in the during the late Permian, what became China and Siberia were on the northeast margins of Pangaea, bordering the Paleo-Tethys Ocean, and two volcanic events arising from China and Siberia are currently favored as key proximate causes of the Permian extinctions.
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