* Astronomy

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RE: Chicxulub event

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Geologist Who Linked Cosmic Strike to Dinosaurs' Extinction Takes Top Prize
Walter Alvarez, the maverick geologist who convinced a skeptical world that dinosaurs and many other living things on Earth were wiped out by a huge fireball from space, has won the highly esteemed Vetlesen Prize. Considered by many the earth sciences equivalent of a Nobel, the $250,000 award is funded by the New York-based G. Unger Vetlesen Foundation and administered by Lamont-Doherty Earth Observatory, a member of Columbia Universitys Earth Institute.

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Geologist Honoured for Earth-Shaking Discovery
A University of California Berkeley professor is being honoured for his theory that a giant meteor wiped out dinosaurs and many other forms of life millions of years ago.

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The impact of a huge meteorite at the end of the Cretaceous period 65 million years ago is generally held responsible for the sudden demise of 60-80% of all species on Earth. But new results challenge the common idea that the extinctions were partly caused by global wildfires triggered by the violent impact.
Claire Belcher and colleagues at Royal Holloway University of London in Surrey, UK, say in a paper in the Proceedings of the National Academy of Sciences USA that the widespread soot deposits in sedimentary rocks formed at the time of the putative impact are not, as previously asserted, evidence of runaway fires caused by the meteorite's impact.

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The theory that dinosaurs were wiped out by an asteroid 65million years ago has been challenged.

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The demise of the dinosaurs probably occurred 300,000 years after a giant meteor struck what is now Mexico, scientists said, casting doubt on a popular theory that the impact triggered a mass extinction.
The Chicxulub crater, which is about 180 kilometres across, was formed on the Yucatan peninsula when an extra-terrestrial object struck Earth 65 million years ago. Since its discovery in 1978, the crater has been cited as evidence that the impacts aftermath led to the extinction of about 65 percent of all species including the dinosaurs.

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But Keller and Addate worried that we were misreading both the geologic and fossil records. They conducted surveys at numerous sites in Mexico, including a spot called El Peñón, near the impact crater. They were especially interested in a 30-ft. layer of sediment just above the iridium layer. That sediment, they calculate, was laid down at a rate of about 0.8 in. to 1.2 in. per thousand years, meaning that all 30 feet took 300,000 years to settle into place.
Analysing the fossils at this small site, they counted 52 distinct species just below the iridium layer. Then they counted the species above it. The result: the same 52. It wasn't until they sampled 30 feet higher - and 300,000 years later - that they saw the die-offs.
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A Princeton University geoscientist who has stirred controversy with her studies challenging a popular theory that an asteroid wiped out the dinosaurs has compiled powerful new evidence asserting her position.
Gerta Keller, whose studies of rock formations at many sites in the United States, Mexico and India have led her to conclude that volcanoes, not a vast meteorite, were the more likely culprits in the demise of the Earth's giant reptiles, is producing new data supporting her claim.

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A burst of carbon monoxide triggered by an asteroid impact may have been a key factor in the mass extinction which saw off the dinosaurs 65 million years ago.
The claim comes from Japanese scientists who have simulated the impact that created the massive crater at Chicxulub on Mexico's Yucatán Peninsula.

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Title: Geological and archaeological implications of strontium isotope analysis of exposed bedrock in the Chicxulub crater basin, northwestern Yucatán, Mexico
Authors: Adrian Gilli, David A. Hodell, George D. Kamenov and Mark Brenner

The surface geology of the site of the Chicxulub impact crater in northwestern Yucatán, Mexico, has not been studied extensively since the discovery of the crater almost two decades ago. Strontium isotope (87Sr/86Sr) measurements in carbonate rock outcrops reveal near-uniform strontium signatures of 0.70905 inside the ring of cenotes (water-filled sinkholes), which represents the rim of the crater basin. Measured strontium isotope ratios were used to infer rock ages, employing the marine Sr isotope curve. We estimate the age of the exposed limestone within the Chicxulub crater basin to be late Miocene to early Pliocene, representing the age of the youngest sediment fill. Discovery of a large terrain of near-uniform strontium isotope ratios in northwestern Yucatán offers new geoarchaeological opportunities to track ancient Maya migration and determine sources of manufactured goods. Our results have implications for applying the Sr isotope method to Maya archaeological sites, such as Mayapán, the last Maya capital, and Chichén Itzá.

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Chicxulub crater