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The Black Sea flood question : changes in coastline, ..
But the branch of the that readers might find most interesting led to humans. Humans are in the phylum, and the last common ancestor that founded the Chordata phylum is still a mystery and understandably a source of controversy. Was our ancestor a ? A ? Peter Ward made the case, as have others for a long time, that it was the sea squirt, also called a tunicate, which in its larval stage resembles a fish. The nerve cord in most bilaterally symmetric animals runs below the belly, not above it, and a sea squirt that never grew up may have been our direct ancestor. Adult tunicates are also highly adapted to extracting oxygen from water, even too much so, with only about 10% of today’s available oxygen extracted in tunicate respiration. It may mean that tunicates adapted to low oxygen conditions early on. Ward’s respiration hypothesis, which makes the case that adapting to low oxygen conditions was an evolutionary spur for animals, will repeatedly reappear in this essay, as will . Ward’s hypothesis may be proven wrong or will not have the key influence that he attributes to it, but it also has plenty going for it. The idea that fluctuating oxygen levels impacted animal evolution has been gaining support in recent years, particularly in light of recent reconstructions of oxygen levels in the eon of complex life, called and , which have yielded broadly similar results, but their variances mean that much more work needs to be performed before on the can be done, if it ever can be. Ward’s basic hypotheses is that when oxygen levels are high, ecosystems are diverse and life is an easy proposition; when oxygen levels are low, animals adapted to high oxygen levels go extinct and the survivors are adapted to low oxygen with body plan changes, and their adaptations helped them dominate after the extinctions. The has a pretty wide range of potential error, particularly in the early years, and it also tracked atmospheric carbon dioxide levels. The challenges to the validity of a model based on data with such a wide range of error are understandable. But some broad trends are unmistakable, as it is with other models, some of which are generally declining carbon dioxide levels, some huge oxygen spikes, and the generally relationship between oxygen and carbon dioxide levels, which a geochemist would expect. The high carbon dioxide level during the Cambrian, of at least 4,000 PPM (the "RCO2" in the below graphic is a ratio of the calculated CO2 levels to today's levels), is what scientists think made the times so hot. (Permission: Peter Ward, June 2014)
During the Cambrian Explosion, an ecosystem developed in which life on the sea floor, surface, and water column all interacted for the first time. All but one of were energy dynamics, as the environment provided either too much or too little energy, and the nutrient hypothesis () will be revisited numerous times in this essay. A lack of nutrients, mineral and otherwise, always meant that the energy-driven dynamics that delivered the nutrients were curtailed. If enough energy is properly applied, all nutrients can be abundant.
Status of the Black Sea flood hypothesis
As with previous critical events, , life helped terraform Earth. But the late Devonian is an instance when the rise of land plants may have also had effects. , which reduced the atmosphere’s carbon dioxide concentration by up to 80%, may have cooled Earth’s surface enough so that an ice age began and another one of Earth’s mass extinctions began. As with the , the ultimate cause for the Devonian extinctions seems to have been rising and falling sea levels, associated with growing and receding ice caps, as . Devonian extinction events began happening more than 380 mya, and a major one happened about 375 mya, called the . The reasons for the Kellwasser event are today generally attributed to the water becoming cold and anoxic.A bolide impact has been invoked in some scientific circles, but .Mountain-building and volcanic events also happened as continents began colliding to eventually form Pangaea (and the resultant silicate and basaltic weathering removed carbon dioxide from the atmosphere), and those dynamics may have been the previous major mass extinction. Black shales abounded during and after the Kellwasser event, and they are always evidence of anoxic conditions and how the oil deposits initially formed. However, the Kellwasser event anoxia may have not only been due to low atmospheric oxygen, but was also the result of eroding the newly exposed land and the detritus of the new forest biomes, which created a vast nutrient runoff into the oceans that may have initiated huge that caused anoxic events near shore.
works for animals that are no more than a couple of millimeters thick, but for larger animals a respiration system was necessary. The rise of the arthropods has been an enduring problem for paleobiologists. Why was the arthropod so successful, particularly in the beginning? Segmented animals dominated Cambrian seas, and segmentation provides for repeated features. Segments obviously became important for locomotion but, for arthropods, segmentation appears to have conferred the more important advantage of distributed oxygen absorption. Each trilobite leg had an attached gill, and leg motion constantly drew fresh oxygenated water over each gill. Arthropods never developed the kinds of lungs that vertebrates have, or the pump gills of fish and other aquatic animals. Early arthropods breathed by moving their legs. Peter Ward’s recent hypothesis is that segments were first used for respiration, to provide a large gill surface area, and using the segments for locomotion came later. For trilobites, the same functionality that pushed water over gills was also coopted for food intake. Also, the leg-mounted gill was necessary because of an arthropod’s body armor; oxygen could not be absorbed through tough exoskeletons.
State of the Environment of the Black Sea - 2009
Recent environmental studies show that disturbed ecosystems can have cascading failures, as the removal of one part of a food chain can in , and entire ecosystems can go extinct. Cascades in today's world usually begin when the apex predator is removed (by humans, and called a ), but not always. Those cascading events can happen in aquatic and environments. Food chains are essentially energy chains , and the more complex they are, the more energy is required to sustain them. The leading hypothesis for why is also an energy-scarcity dynamic. Also, the most compelling findings that I have encountered regarding degenerative disease in humans shows that if individual cells no longer have their nutritional needs met by the organism, they stop acting out their role as specialized cells and “.” It may be difficult-to-impossible for scientists to reconstruct and test cascading failure hypotheses in ancient mass extinction events, but they may have played a major role in them, if not the dominant role.
After several million years of adaptation, tetrapods seemed ready to become the dominant land animals, but then came the second major Devonian extinction event, today called the . While the ice age conditions around the Kellwasser event are debated, there is no uncertainty about the Hangenberg event; there were massive, continental ice sheets, accompanied by falling sea levels and anoxic events, as evidenced by huge black shales. The event’s frigidity was probably a key extinction factor, and anoxia was the other killing mechanism. The Hangenberg event had ; it meant , the near-extinction of the (perhaps only one genus survived), oceanic went extinct, trilobites began to make their exit as seafloor communities were devastated, lobe-finned fish reached their peak influence, and forests collapsed.
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Catastrophic flooding of the Black Sea | Lamont …
Wrangham’s hypothesis is more robust and subtle than this essay can do justice to, but I will survey some of the findings, implications, and controversy. Raw food has various nutritional properties that are superior to cooked food, such as vitamins, but because cooked food provides more digestible calories for humans than raw food, it represented an evolutionary advantage. Meat, starches, and seeds are far more digestible when cooked, and are much easier to chew. Today, chimps in will not eat raw seeds of trees, but when a fire passes through the savanna, they search the ground below the trees and eat their cooked seeds.
about the Black Sea: the Black Sea deluge hypothesis ..
Just as precipitation before plants colonized land, denuded lands and , and transpiration no longer contributed to the hydrological cycle. Rampant deforestation contributed to flooded Mesopotamian rivers, and the region also became drier. The flood that survived, which , was probably related to deforestation, although a great deal of speculation exists regarding the origins of flood myths. The , where the rising interglacial global ocean flooded the lake to levels higher than during the glacial period. Another hypothesis has rising seas flooding the lower end of Mesopotamia. There are arguments that the legend of Atlantis related to a seashore civilization drowned under a rising interglacial ocean, but I think that an increasingly deforested Sumerian hinterland gave rise to the floods of legend.
Young Danube delta documents stable Black Sea level since the ..
The cause of the cooling at 14 mya is the subject of a number of hypotheses, one of which is mountain-building in that created by colliding continents exposed rock that then absorbed carbon dioxide from the atmosphere in . Around the time of the cooling, the Arabian Peninsula finally crashed into Asia and closed off the Tethys Ocean, which by then was more like the Tethys Strait there. The last remnants of the Tethys consisted of an inland sea that includes today’s Caspian, Black, and Aral seas, and the Mediterranean Sea and Persian Gulf.
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