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Shop Skeptic: The Medea Hypothesis, by Dr. Peter Ward
Because the Western Hemisphere’s inhabitants were virtually all in their Stone Age, they as greatly as Old World civilizations did, and many societies were environmentally sustainable and provided seeming answers to questions that scientists have asked about Old World civilizations’ development. The natives of coastal California were familiar with agriculture, as it was practiced by nearby inland tribes, but they never adopted it. California was so bountiful, and its climate was so human-friendly, that its natives retained their hunter-gatherer lifestyle. Similarly, northward on the Pacific Northwest's coast, natives created an economy in which half of its calories derived from salmon runs, and those peoples were relatively sedentary without agriculture. Natives turned the Great Plains into a big pasture for bison, and the biome was partly maintained by annual burning of the grasslands. In Mesoamerica, farming has been sustainable for thousands of years. In the Amazon, the natives transformed the rainforest, and a higher proportion of plants and trees provided human-digestible foods than in any other “wild” place on Earth, those natives also terraformed thin tropical soils with ceramics (maybe unintentional) and charcoals (intentional) and made super-soils called and . In summary, native practices in the Western Hemisphere were often sustainable if not quite abundant. But when civilizations arose, they had problems that were like their Old World counterparts'. Their problems were also environmental and not just the injustices of hierarchal societies, often steeply hierarchical.
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Dymocks - The Medea Hypothesis by Peter Ward
There is also evidence that life itself can contribute to mass extinctions. When the eventually , organisms that could not survive or thrive around oxygen (called ) . When anoxic conditions appeared, particularly when existed, the anaerobes could abound once again, and when thrived, usually arising from ocean sediments, they . Since the ocean floor had already become anoxic, the seafloor was already a dead zone, so little harm was done there. The hydrogen sulfide became lethal when it rose in the and killed off surface life and then wafted into the air and near shore. But the greatest harm to life may have been inflicted when hydrogen sulfide eventually , which could have been the final blow to an already stressed ecosphere. That may seem a fanciful scenario, but there is evidence for it. There is fossil evidence of during the Permian extinction, as well as photosynthesizing anaerobic bacteria ( and ), which could have only thrived in sulfide-rich anoxic surface waters. Peter Ward made this key evidence for his , and he has implicated hydrogen sulfide events in most major mass extinctions. An important aspect of Ward’s Medea hypothesis work is that about 1,000 PPM of carbon dioxide in the atmosphere, which might be reached in this century if we keep burning fossil fuels, may artificially induce Canfield Oceans and result in . Those are not wild-eyed doomsday speculations, but logical outcomes of current trends and , proposed by leading scientists. Hundreds of already exist on Earth, which are primarily manmade. Even if those events are “only” 10% likely to happen in the next century, that we are flirting with them at all should make us shudder, for a few reasons, one of which is the awesome damage that it would inflict on the biosphere, including humanity, and another is that it is entirely preventable with the use of technologies .
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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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07/07/2016 · Peter Ward (paleontologist)'s wiki: ..
One of Peter Ward’s recent hypotheses is that animals that adapted to the changing conditions, particularly when oxygen levels crashed, survived the catastrophes to dominate the post-catastrophic environment. In the late Permian, several therapsid lines developed , which may have been used for respiratory water retention in a world where oxygen levels were crashing. This is a controversial issue, and related to the controversy over when reptiles developed . The therapsid ancestors of mammals, , first appeared about 260 mya, and had many .
Energy and the Human Journey: Where We Have Been; …
The (c. 5.3 to 2.6 mya) began warmer than , but was the prelude to today’s ice age, as temperatures steadily declined. An epoch of less than three million years reflects human interest in the recent past. Geologically and climatically, there was little noteworthy about the Pliocene (although the was created then), although two related events made for one of the most interesting evolutionary events yet studied. South America kept moving northward, and the currents that once in the Tethyan heyday were finally closed. The gap between North America and South America began to close about 3.5 mya, and by 2.7 mya the current land bridge had developed. Around three mya, the began, when fauna from each continent could raft or swim to the other side. South America had been isolated for 60 million years and only received the stray migrant, such as rodents and New World monkeys. North America, however, received repeated invasions from Asia and had exchanges with Europe and Greenland. North America also had much more diverse biomes than South America's, even though it had nothing like the Amazon rainforest. The ending of South America’s isolation provided the closest thing to a controlled experiment that paleobiologists would ever have. South America's fauna was devastated, far worse than European and African fauna were when Asia finally connected with them. More than 80% of all South American mammalian families and genera existing before the Oligocene were extinct by the Pleistocene. Proboscideans continued their spectacular success after leaving Africa, and species inhabited the warm, moist Amazonian biome, as well as the Andean mountainous terrain and pampas. The also invaded and thrived as a mixed feeder, grazing or browsing as conditions permitted. In came cats, dogs, camels (which became the ), horses, pigs, rabbits, raccoons, squirrels, deer, bears, tapirs, and others. They displaced virtually all species inhabiting the same niches on the South American side. All large South American predators were driven to extinction, as well as almost all browsers and grazers of the grasslands. The South American animals that migrated northward and survived in North America were almost always those that inhabited niches that no North American animal did, such as monkeys, (which survived because of their claws), and their small cousins (which survived because of their armor), , and (which survived because of their quills). The opossum was nearly eradicated by North American competition but survived and is the only marsupial that made it to North America and exists today. One large-hoofed herbivore survived: the . The (it weighed one metric ton!) survived for a million years after the interchange. , that , also survived and migrated to North America and lasted about a million years before dying out. In general, North American mammals were , which resulted from evolutionary pressures that South America had less of, in its isolation. They were able to outrun and outthink their South American competitors. South American animals made it past South America, but none of them drove any northern indigenous species of note to extinction.