Cretaceous Period | Definition, Climate, Dinosaurs, & …
Compile a list of the evidence supporting the impact hypothesis as the cause of the Cretaceous mass extinction.
Energy and the Human Journey: Where We Have Been; …
Just as the aftermath of the appearance of complex life was uninteresting from a , as the amazingly diverse energy-generation strategies of archaea and bacteria were almost totally abandoned in favor of aerobic respiration, biological solutions to the problems that complex life presented were greatest during the Cambrian Explosion, and everything transpiring since then has been relatively insignificant. Animals would never see that level of innovation again. While investigating those eonic changes, many scientists have realized that the dynamics of those times might have been quite different from today’s, as once again may be of limited use for explaining what happened. Also, scientists generally use a rule-of-thumb called , or parsimony, which states that with all else being equal, simpler theories are preferred. , a seminal theorist regarding the scientific method, as they were easier to falsify. However, this issue presents many problems, and in recent times, theories of or speciation have invoked numerous interacting dynamics. Einstein noted that the more elegant and impressive the math used to support a theory, the less likely the theory depicted reality. Occam’s Razor has also become an unfortunate dogma in various circles, particularly , in which the of materialism and establishment science are defended, and often quite irrationally. Simplicity and complexity have been seesawing over the course of scientific history as fundamental principles. The recent trend toward multidisciplinary syntheses has been generally making hypotheses more complex and difficult to test, although and ever-increasing and more precise data makes the task more feasible than ever, at least situations in which are not interfering.
In the 19th century, the Jurassic was called the Golden Age of Dinosaurs, but that moniker is arguably most applicable to the late Cretaceous, and it was a golden age clear up until a bolide impact brought it all to an end. One of the uglier disputes in paleontology’s history was a bent on outcompeting each other in finding and describing dinosaur fossils. However, the dinosaur extinction is probably the largest and most contentious controversy in the history of paleontology. Again, the , due to Lyell’s and Darwin’s prevailing uniformitarianism, until my lifetime. The hypothesized bolide event, , was a kind of a bolide event inflicted on paleontology. Acrimonious disputes ignited that still burn, but it made studying mass extinctions respectable. Initially attacked and dismissed, the bolide impact hypothesis is by far today’s leading hypothesis for explaining the . However, at the same time, India was speeding toward its Asian destiny, and its movement is associated with . Also, , so the bolide event has some theoretical competition as a causative agent.
Climate Change Catastrophes in Critical Thinking
Only when economic surpluses (primarily food) were redistributed, first by chiefs and then by early states, did men rise to dominance in those agricultural civilizations. Because the rise of civilization in the Fertile Crescent is the best studied and had the greatest influence on humanity, this chapter will tend to focus on it, although it will also survey similarities and differences with other regions where agriculture and civilization first appeared. Whenever agriculture appeared, cities nearly always eventually appeared, usually a few thousand years later. Agriculture’s chief virtue was that it extracted vast amounts of human-digestible energy from the land, and population densities hundreds of times greater than that of hunter-gatherers became feasible. The , but today it is widely thought that population pressures led to agriculture's appearance. The attractions of agricultural life over the hunter-gatherer lifestyle were not immediately evident, at least after the first easy phase, when intact forests and soils were there for the plundering. On the advancing front of agricultural expansion, life was easy, but as forests and soils were depleted, population pressures led to disease, "pests" learned to consume that human-raised food, and agricultural life became a life of drudgery compared to the hunter-gatherer or horticultural lifestyle. Sanitation issues, disease, and environmental decline plagued early settlements, and not long after they transitioned from hunter-gatherers to farmers, but the land could also support many times the people. Another aspect of biology that applies to human civilization is the idea of . Over history, the society with the higher carrying capacity prevailed, and the loser either adopted the winner’s practices or became enslaved, taxed, marginalized, or extinct. On the eve of the Domestication Revolution, Earth’s carrying capacity with the hunter-gatherer lifestyle was around 10 million people, and the actual population was somewhat less, maybe . On the eve of the Industrial Revolution in 1800, Earth’s population was , and again was considered to be about half of Earth's carrying capacity under that energy regime. No matter how talented a hunter-gatherer warrior was, he was no match for two hundred peasants armed with hoes.
The (c. 15 kya to 11.8 kya) succeeded the Kebaran culture. The Natufian village at in today’s Syria was established about 13.5 kya and was situated on a gazelle migration route. The residents of that village of a few hundred people also . Those villagers became Earth’s first known farmers, and they had dogs. The during the Younger Dryas and resettled after it ended. The effect of a harsher climate may have , which began there about 11 kya. By seven kya, the settlement had grown to several thousand people, and was then abandoned due to aridity. No evidence of warfare is associated with the settlement. A compelling recent hypothesis is that agriculture could not have developed in warfare’s presence, as farmers would have been too vulnerable to raids by hungry hunters. In the four places on Earth where civilization seems to have independently developed: the Fertile Crescent, China, Mesoamerica, and the Andes, no evidence of violent conflict exists before those civilizations, fed by the first crops, began growing into states. Those states are called “pristine” states, as no other states influenced their development. Also, it is considered likely that a primary impetus for beginning agriculture in those regions was the decimation of animals to hunt. Not only was the easy meat rendered largely extinct, but those animals would have also been competitors for crops. The peaceful agricultural villages that , in which women's status was closer to men's than at any time before the Industrial Revolution, actually existed, if only for a relatively brief time, in only a few places.
Ornithology Lecture Notes 1 - Introduction to Birds & …
What human-agency skeptics have ignored or argued around are unique features of the megafauna that went extinct the humans that preyed on them, while they examined minutia. ever before humans arrived. As , African elephants help create the biomes they live in, as terraforming agents. They were far from idle browsers and grazers, but had outsized impacts on the vegetation, soils, and geological features such as water holes. Dinosaurs may have had similar biome impacts, and it was probably a feature of that large herbivore guild. Scientists have been finding plenty of evidence that vegetation changes that human-agency skeptics attribute to climate change may well be largely the of the guild’s disappearance, not a cause. Researchers in Africa have also discovered that changes wrought by elephants created biomes dependent on elephant management. When elephants disappeared, so did the biomes that they created, which is why smaller species could also disappear when the large herbivore guild vanished. Although Australia was the only non-Antarctic continent without proboscideans 50 kya, and its guilds were comprised of somewhat smaller animals, probably reflecting inherent differences between placental and marsupial mammals, Australia's large herbivores probably had similar biome impacts.
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.
supports the hypothesis that ..
16/01/2018 · Meteorite Impact and Dinosaur Extinction
Dinosaur - Wikipedia
evidence that supports the impact hypothesis.
15/04/2010 · Earth's five mass extinction events Posted on 15 April 2010 by John Cook
Evolution: Extinction: What Killed the Dinosaurs? - PBS
Origin of Angiosperms
13/01/2018 · What Killed the Dinosaurs
The ecosystems may not have recovered from Olson’s Extinction of 270 mya, and at 260 mya came another mass extinction that is called the mid-Permian or extinction, or the , although a recent study found only one extinction event, in the mid-Capitanian. In the 1990s, the extinction was thought to result from falling sea levels. But the first of the two huge volcanic events coincided with the event, in . There can be several deadly outcomes of major volcanic events. As with an , massive volcanic events can block sunlight with the ash and create wintry conditions in the middle of summer. That alone can cause catastrophic conditions for life, but that is only one potential outcome of volcanism. What probably had far greater impact were the gases belched into the air. As oxygen levels crashed in the late Permian, there was also a huge carbon dioxide spike, as shown by , and the late-Permian volcanism is the near-unanimous choice as the primary reason. That would have helped create super-greenhouse conditions that perhaps came right on the heels of the volcanic winter. Not only would carbon dioxide vent from the mantle, as with all volcanism, but the late-Permian volcanism occurred beneath Ediacaran and Cambrian hydrocarbon deposits, which burned them and spewed even more carbon dioxide into the atmosphere. Not only that, great salt deposits from the Cambrian Period were also burned via the volcanism, which created hydrochloric acid clouds. Volcanoes also spew sulfur, which reacts with oxygen and water to form . The oceans around the volcanoes would have become acidic, and that fire-and-brimstone brew would have also showered the land. Not only that, but the warming initiated by the initial carbon dioxide spike could have then warmed up the oceans enough so that methane hydrates were liberated and create even more global warming. Such global warming apparently warmed the poles, which not only melted away the last ice caps and ended an ice age that had , but deciduous forests are in evidence at high latitudes. A 100-million-year Icehouse Earth period ended and a 200-million-year Greenhouse Earth period began, but the transition appears to have been chaotic, with wild swings in greenhouse gas levels and global temperatures. Warming the poles would have lessened the heat differential between the equator and poles and further diminished the lazy Panthalassic currents. The landlocked Paleo-Tethys and Tethys oceans, and perhaps even the Panthalassic Ocean, may have all become superheated and anoxic as the currents died. Huge also happened, which may have and led to ultraviolet light damage to land plants and animals. That was all on top of the oxygen crash. With the current state of research, all of the above events may have happened, in the greatest confluence of life-hostile conditions during the eon of complex life. A recent study suggests that the extinction event that ended the Permian may have lasted only 60,000 years or so. In 2001, a bolide event was proposed for the Permian extinction with great fanfare, but it does not appear to be related to the Permian extinction; the other dynamics would have been quite sufficient. The Permian extinction was the greatest catastrophe that Earth’s life experienced since the previous supercontinent existed in the .
Evidence for the Asteroid Impact Hypothesis
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)
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