THE K-T EXTINCTION

The resulting profile showing the depth variation of m is displayed in Fig. In a dynamical calculation in which silicate material is transported through these depths and undergoes these phase changes, two effects need to be taken into account. One is the latent heat released or absorbed and the other is the deflection of the phase boundary upward or downward. The latent heat may be accounted for by locally adding or removing heat through the volume heating term in equation 3 proportional to the vertical flux of material through the transition depth. The deflection in the location of a phase boundary occurs because the pressure, and therefore the depth, at which the phase change occurs depends on the temperature. The effect of such a deflection enters as a contribution to the buoyancy term in equation 1.

Jüngere Dryaszeit

See geologic time scale for an overview of these time periods. These and a pair of other extinction events acting as “book ends” for the Big Five are highlighted below: End Ordovician extinction about million years ago. Two Ordovician-Silurian extinction events occurred, probably as the result of a period of glaciation. Marine habitats changed drastically as sea levels decreased causing the first die-off, and then, when sea levels rose rapidly between five hundred thousand to a million years later, a second great die-off occurred.

On hypothesis is that a gamma ray burst may have triggered this extinction Jha

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Could not subscribe, try again laterInvalid Email Frogs leaped to take advantage of the global catastrophe that killed off the dinosaurs, scientists have discovered. Nearly nine out of 10 of the amphibian species are descended from just three lineages that survived the mass extinction. Each of them jumped forward precisely at the junction of the Cretaceous and Paleogene periods – formerly known as the KT boundary – when the disaster happened.

The first survivors may have ridden out the meteor strike by burrowing underground, the scientists believe. Thereafter, it was arboreal tree frogs that led the way by exploiting newly available habitat niches. Meteor strike is thought to have shaken Earth so much it created a surge of volcanic activity Image: Scientists reveal species could have survived if killer asteroid had hit 30 seconds later Previous research had suggested that frog evolution took off 35 million years earlier and had nothing to do with the dinosaur apocalypse.

PA Dinosaurs were ALREADY dying out before a giant asteroid finished them off, scientist claims Trees are an ideal habitat for frogs not only because they provide a refuge from terrestrial predators, leaf cover on the ground, and abundant insects for food, said the researchers whose findings are reported in the journal Proceedings of the National Academy of Sciences. American and Chinese scientists made the discovery after analysing genetic data from frogs within 44 living families. Today’s frogs comprising more than 6, known species, are increasingly threatened by habitat destruction, increasing human population, and climate change.

They provide ecological opportunity for new things. Just wait for the next grand extinction and life will take off again.

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Evidence for an impact at the K/T boundary. History of the impact theory as the cause of the Cretaceous/Tertiary extinction 65 million years ago begins in the Italian town of .

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How Good Are Those Young-Earth Arguments?

Tertiary mammals of the western United States 4. Tertiary bird and mammal tracks and the Devils corkscrews 5. Tertiary volcanism in the northwest United States 6. Six main evidences are used to support the hypothesis and these are listed in table 1. They argue that such trends would not have occurred during the Flood but only afterwards.

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As shown in “Administrative Subdivisions of Countries”. Alpha-2 codes from ISO A Codes from the U. Codes assigned by the International Olympics Committee. These codes identify the nationality of athletes and teams during Olympic events. Distinguishing signs of vehicles in international traffic oval bumper sticker codes WMO: This column is just a superficial note, provided for convenience. I don’t care to argue about it.

For full details, please consult your favorite official source. Its list is coordinated with a list of countries used by the United Nations Statistics Division for reporting purposes.

THE K-T EXTINCTION

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Evidence of the ‘Lost World’ — did dinosaurs survive the end Cretaceous extinctions? April 28, The Lost World, Sir Arthur Conan Doyle’s account of an isolated community of dinosaurs that survived the catastrophic extinction event 65 million years ago, has no less appeal now than it did when it was written a century Dinosaurs declined before mass extinction April 30, Dinosaurs were dying out much earlier than the mass extinction event 65 million years ago, Natural History Museum scientists report in the Proceedings of the Royal Society journal today.

Each other October 15, It turns out that the undisputed king of the dinosaurs, Tyrannosaurus rex, didn’t just eat other dinosaurs but also each other. Paleontologists from the United States and Canada have found bite marks on the giants’ bones Longest dinosaur thigh bone in Europe found in Spain September 24, Palaeontologists in Spain have found the fossiled thigh bone of a dinosaur that is almost two metres in length, the longest such femur ever discovered in Europe, they said Friday.

Mummified dinosaur skin yields up new secrets July 1, PhysOrg. Recommended for you New Egyptian dinosaur reveals ancient link between Africa and Europe January 29, When it comes to the final days of the dinosaurs, Africa is something of a blank page. Fossils found in Africa from the Late Cretaceous, the time period from to 66 million years ago, are few and far between.

Cretaceous–Paleogene boundary

Print The mass extinction event that occurred about 65 million years ago brought about an end to the domination of the planet by reptiles and, in so doing, opened up ecological niches within which mammals flourished several million years later including, happily, human beings! The Mesozoic Era begins about million years ago after the end-Permian mass extinction event.

The rock sequence preserved in a gorge outside of Gubbio preserves the transition between the Cretaceous and Tertiary periods. The site was visited by geologists conducting paleomagnetic surveys used to make precise dates of geologic horizons.

Ar dating is cheaper, and is more widely useable in a greater variety of geologic settings, than most other deep time radiometric dating techniques. But geochemists have been suspicious that it might give slightly anomalous results: specifically, results that are just a little (~1%) too young.

The debate over the cause of the K-Pg extinction has continued to simmer through the years, boiling over at times as proponents of each explanation traded barbs in the literature and at scientific meetings. The position and inferred age of the crater — named after Chicxulub Puerto, the coastal town near its center — matched up with the patterns and timing of fallout observed at Gubbio and a host of other such sites.

The Chicxulub crater and its debris quickly became the keystone argument of impact hypothesis proponents. Other evidence from the geologic record also points to a major disturbance on Earth at about the same time as this huge pulse of extinction: A sudden shift in carbon isotopic ratios and a decrease in the amount of calcite observed in marine sediment cores indicate drastic drops in biological productivity and carbonate sedimentation in the oceans — markers traditionally taken to define the K-Pg boundary.

At certain locations on land, layers of sediment enriched in iridium and other rare metals, as well as bits of shocked quartz and droplet-shaped particles called tektites — which form when melted rock resolidifies quickly as it flies through the air — indicate that something big struck the planet around the same time that the extinctions were occurring.

At the K-T boundary.