Argon-argon dating, developed at UC Berkeley in the s, is based on the fact that the naturally-occurring isotope potassium decays to argon with a 1.
Single-grain rock samples are irradiated with neutrons to convert potassium to argon, which is normally not present in nature. The ratio of argon to argon then provides a measurement of the age of the sample. University of California - Berkeley Tweet Favorites Email Print PDF Researchers examine how musicians communicate non-verbally during performance January 18, A team of researchers from McMaster University has discovered a new technique to examine how musicians intuitively coordinate with one another during a performance, silently predicting how each will express the music.
Childcare can be expensive, stressful, and annoying to organise, but a University of Otago-led study has found it may also be behind religion's resilience. Separate skeletons suggested to be from different early hominin species are, in fact, from the same species, a team of anthropologists has concluded in a comprehensive analysis of remains first discovered a decade ago.
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Refining the date of the K/T boundary and the dinosaur extinction
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Notify me of new comments via email. A science blog for non-scientists, by a rambling biologist and paleoartist. Home About Julius T. Csotonyi Why This Blog? Tylosaurus and the K-T impact event at the end of the Cretaceous. Csotonyi Nevertheless, the vast majority of dinosaurs the non-avian dinosaurs died around 65 million years ago. Pachycephalosaurus and the approaching K-T asteroid, visible as a bright star. Csotonyi However, it now seems as though dinosaurs may have been more tenacious than originally thought.
Darwinius masillae, an early primate. A recently deceased Brachylophosaurus, about to become entombed and ultimately fossilized by river sediments. Csotonyi Given the difficulty of fossilization, it is not surprising that paleontologists have found a gap in the dinosaur fossil record prior to the Cretaceous extinction event which can be detected by anomalies in the distribution of fossilized pollen, as well as often the presence of the element iridium, which is found at higher concentration in meteorites.
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Since July 1, Fleshing Out the Past: One of the consequences of such an impact is a dust cloud which would block sunlight and inhibit photosynthesis for a few years. This would account for the extinction of plants and phytoplankton and of organisms dependent on them including predatory animals as well as herbivores.
However, small creatures whose food chains were based on detritus might have still had a reasonable chance of survival. It would have taken at least ten years for those aerosols to dissipate. Global firestorms may have resulted as incendiary fragments from the blast fell back to Earth.
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This high O 2 level would have supported intense combustion. The level of atmospheric O 2 plummeted in the early Paleogene Period. If widespread fires occurred, they would have increased the CO 2 content of the atmosphere and caused a temporary greenhouse effect once the dust cloud settled, and this would have exterminated the most vulnerable survivors of the "long winter". The impact may also have produced acid rain , depending on what type of rock the asteroid struck. However, recent research suggests this effect was relatively minor.
Chemical buffers would have limited the changes, and the survival of animals vulnerable to acid rain effects such as frogs indicates that this was not a major contributor to extinction. Impact theories can only explain very rapid extinctions, since the dust clouds and possible sulphuric aerosols would wash out of the atmosphere in a fairly short time—possibly under ten years. When it was originally proposed, one issue with the " Alvarez hypothesis " as it came to be known had been that no documented crater matched the event.
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It makes the feature the second of the largest confirmed impact structures on Earth , and the only one whose peak ring is intact and directly accessible for scientific research. Penfield was initially unable to obtain evidence that the geological feature was a crater and gave up his search. Later, through contact with Alan Hildebrand in , Penfield obtained samples that suggested it was an impact feature.
Evidence for the impact origin of the crater includes shocked quartz ,  a gravity anomaly , and tektites in surrounding areas. In , a scientific drilling project drilled deep into the peak ring of the impact crater, hundreds of meters below the current sea floor, to obtain rock core samples from the impact itself. The discoveries were widely seen as confirming current theories related to both the crater impact and its effects.
The shape and location of the crater indicate further causes of devastation in addition to the dust cloud. The asteroid landed right on the coast and would have caused gigantic tsunamis , for which evidence has been found all around the coast of the Caribbean and eastern United States—marine sand in locations which were then inland, and vegetation debris and terrestrial rocks in marine sediments dated to the time of the impact.
This would have further reduced the sunlight reaching the Earth's surface and then over several days, precipitated planet-wide as acid rain , killing vegetation, plankton and organisms which build shells from calcium carbonate coccolithophorids and molluscs. However, there is evidence that two thirds of the Deccan Traps were created within 1 million years about The Deccan Traps could have caused extinction through several mechanisms, including the release of dust and sulphuric aerosols into the air which might have blocked sunlight and thereby reduced photosynthesis in plants.
In addition, Deccan Trap volcanism might have resulted in carbon dioxide emissions which would have increased the greenhouse effect when the dust and aerosols cleared from the atmosphere. In the years when the Deccan Traps theory was linked to a slower extinction, Luis Alvarez who died in replied that paleontologists were being misled by sparse data.
While his assertion was not initially well-received, later intensive field studies of fossil beds lent weight to his claim.
K-T Boundary - Universe Today
Eventually, most paleontologists began to accept the idea that the mass extinctions at the end of the Cretaceous were largely or at least partly due to a massive Earth impact. However, even Walter Alvarez has acknowledged that there were other major changes on Earth even before the impact, such as a drop in sea level and massive volcanic eruptions that produced the Indian Deccan Traps, and these may have contributed to the extinctions.
Several other craters also appear to have been formed about the time of the K—Pg boundary.
This suggests the possibility of nearly simultaneous multiple impacts, perhaps from a fragmented asteroidal object, similar to the Shoemaker—Levy 9 cometary impact with Jupiter. Any other craters that might have formed in the Tethys Ocean would have been obscured by erosion and tectonic events such as the relentless northward drift of Africa and India.