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Cretaceous extinctions: the volcanic hypothesis.
Although great mass death resulted from the end-Triassic extinction, dinosaurs emerged virtually unscathed. Why? It may have been due to their superior , which could survive the hot times and record-low oxygen levels of the end-Triassic. The mammalian lung is pretty good, too, but not nearly as efficient as the saurischian dinosaurs’ air sac system. Crocodiles have a piston-lung like mammals have, so they also have a superior respiration system. Mammals rode out the storm in their burrows while crocodile ancestors cooled in the swamps and marine reptiles cooled in the oceans. Living in burrows, swamps, and other refugia is probably how mammals, crocodiles, and birds survived the when non-avian dinosaurs did not.
What was most relevant to humans, however, was the almost-complete extinction during the Kellwasser event of the tetrapods that had come ashore. Tetrapods did not reappear in the fossil record until several million years after the Kellwasser event, and has even been referred to as the Fammenian Gap (the is the Devonian’s last age). The Kellwasser event also appeared to be a period of low atmospheric oxygen content, and some evidence is the lack of charcoal in fossil deposits. Recent research has demonstrated that getting wood to burn at oxygen levels of less than 13-15% may be impossible. Because all periods of complex land life show evidence of forest fires, it is today thought that oxygen levels have not dropped below 13-15% since the Devonian, but during the “charcoal gap” of the late Devonian, when the first landlubbing tetrapods went extinct, oxygen levels reached their lowest levels since the , which must have impacted the first animals trying to breathe air instead of water. During the , there is no charcoal evidence at all, which leads to the notion that oxygen levels may have even dropped below 13%. This drop may be related to severe climatic stresses on the new forests, which are probably related to the ice age that the forests helped bring about due to their carbon sequestering. That is an attractively explanatory scenario, but the continues. The first seed plants probably appeared before the Kellwasser event, but it was not until after the Fammenian Gap that seed plants began to proliferate.
Causes of the Cretaceous Extinction
Although the best-known cause of a mass extinction is the asteroid impact that killed off the non-avian dinosaurs, in fact, volcanic activity seems to have wreaked much more havoc on Earth's biota. Volcanic activity is implicated in at least four mass extinctions, while an asteroid is a suspect in just one. And even in that case, it's difficult to disentangle how much of the end-Cretaceous extinction was caused by the asteroid and how much was caused by the steady ooze of lava that was blanketing most of India at around the same time.
The Cretaceous-Tertiary mass extinction - also known as the K/T extinction - is famed for the death of the dinosaurs. However, many other organisms perished at the end of the Cretaceous including the ammonites, many flowering plants and the last of the pterosaurs. Some groups had been in decline for several million years before the final event that destroyed them all. It's suggested that the decline was due to flood basalt eruptions affecting the world's climate, combined with drastic falls in sea level. Then a huge asteroid or comet struck the seabed near the Yucatan Peninsula in Mexico and was the straw that broke the camel's back.
Speculated Causes of the End-Cretaceous Extinction ..
Above all else, life is an energy acquisition process. All life exploits the potential energy in various atomic and molecular arrangements, or captures energy directly, as in photosynthesis. Early life exploited the . The chemosynthetic ideal is capturing chemicals fresh to new environments that have yet to react with other chemicals. The currently most-accepted hypothesis has life first appearing on Earth about 3.5-3.8 bya, probably in volcanic vents on the ocean floor. The earliest life forms took advantage of fresh chemicals introduced to the oceans. Life had to be opportunistic and quick in order to capture that energy before other molecules did.
Carbon dioxide, on the other hand, has been generally decreasing as an atmospheric gas for billions of years, and has . The geochemical process is like nitrogen's in that atmospheric water combines with carbon dioxide to form a weak acid, which then falls to Earth in precipitation. But carbon is in the same elemental family as an abundant crustal element: . in crustal compounds and turns into in a process called . Most of Earth’s was probably removed by this process, although the exact mechanisms are in dispute. In all paleoclimate studies, carbon dioxide is a prominent variable, if not prominent variable, for determining Earth’s surface temperature. But perhaps as early as three bya, life became a significant source of carbon removal from the atmosphere, as life forms died and sank to the ocean floor, were subsequently buried by , and further buried them into Earth’s crust and mantle.
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THE CRETACEOUS–TERTIARY MASS EXTINCTION: …
Andrew Glikson, an earth and palaeoclimate scientist at the Australian National Univeristy, thinks the volcanism triggered by the asteroid strike wasn’t confined to India. Another area worth examining is the Hawaiian chain, he says. “It was reactivated 66 million years ago, so there was some effect there, for sure.” Renne’s meticulous analyses might determine if the Hawaii boost happened before or after the asteroid, lending even more weight to the theory that the asteroid triggered volcanos that annihilated the dinosaurs – and perhaps put a decades-long debate to rest.
THE CRETACEOUS–TERTIARY MASS EXTINCTION: THEORIES AND CONTROVERSIES
I’m unsure weather our data will help you but Our International Paleo-chronology Gp. has been actively radiocarbon dating dinosaur bones and fossil wood from the Cretaceous and the Jurassic periods and the ages are all the same in the range of 22,000 to 40,000 year. These links should help I would think. and Two other teams have recently confirmed our results. Another team I was on in 1987 and 1989 started this research.
Cretaceous Period | Definition, Climate, Dinosaurs, & …
More carbon dioxide was removed from the atmosphere by those processes than was reintroduced to the atmosphere by volcanism and other processes. That removal and reintroduction of carbon to Earth’s surface is called the . As carbon dioxide continues to be removed from the atmosphere, life will have a harder time surviving, to eventually go extinct, as first plants, then animals decline and go extinct, and it will be back to microbes ruling the Earth until the Sun’s expansion into a red giant destroys Earth. The earthly end of complex life’s reign may be a billion years away, but might come much sooner.
Volcanic Eruptions The fourth and final ..
The Moon in relation to the Sun and made Earth's seasons vary within a relatively narrow range. Without the Moon, Earth could have up to 90o changes in its axis of rotation instead of the 22o-to-24.5o variation of the past several million years. If that had happened, although life may have survived, Earth’s climate would have been extremely chaotic, with part of the planet going into perpetual day while another went into perpetual night, and other wild variations. Earth would have had mass-extinction effects on those portions, and the rest of the biosphere would have been extremely challenged to survive. Complex life on Earth would little resemble today’s (if it had appeared and survived at all), if Earth’s axis tilted chaotically and severely. The primary effect of Earth’s stable tilt is the planet’s entire surface receiving relatively uniform and predictable energy levels.
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