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Blobrana


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Ancient grass 'frozen in time' by space impact

Ancient plant material was perfectly preserved in the glass formed when asteroids hit the Earth millions of years ago, scientists report.
The "frozen in aspic" appearance of what are apparently blades of grass is spectacular enough.
But a team writing in Geology journal says that delicate organic chemicals have also been conserved inside.
Incredibly, the searing heat generated when the space rock hit was responsible for the remarkable preservation.
The findings could even point to a new way of searching for past life on Mars.
The impact glasses examined in this study come from the Pampas of Argentina and have a range of dates under 10 million years old - with many dating to the Miocene Period.
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Blobrana


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Geologists assess deep impacts of near-Earth object strikes

Volcanologists from the Universities of Leicester and Durham have forensically reconstructed the impact of a meteorite on Earth and how debris was hurled from the crater to devastate the surrounding region.
New research by Mike Branney, of the University of Leicester's Department of Geology,  and Richard Brown, University of Durham,  shows that some aspects of giant meteorite impacts onto Earth may mimic the behaviour of large volcanic eruptions.
Meteorite impacts are more common than is popularly appreciated - but what happens when the meteorite hits?  Direct observation is understandably difficult, but researchers pick through impact debris that has been spared the ravages of erosion, to forensically reconstruct the catastrophic events.
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Blobrana


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Potential meteor menace overstated

A big question is: are impacts periodic? That is, do they happen with some repeating period? If so, then there must be some astrophysical cause: a giant planet in the outer solar system, for example, that shakes loose comets every 50 million years, or the Sun passing near another star. This has been studied, and all kinds of periods have been found in the data. I've always been a little skeptical of them, since the data are sparse. And now it looks like my thoughts are being supported: a new study finds no such pattern in the ages of craters, and concludes all the periods found previously are probably due to errors in the analyses.
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Blobrana


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Avoiding Nemesis: Does the impact rate for asteroids and comets vary periodically with time?

Is the Earth more likely or less likely to be hit by an asteroid or comet now as compared to, say, 20 million years ago? Several studies have claimed to have found periodic variations, with the probability of giant impacts increasing and decreasing in a regular pattern. Now a new analysis by Coryn Bailer-Jones from the Max Planck Institute for Astronomy (MPIA), published in the Monthly Notes of the Royal Astronomical Society, shows those simple periodic patterns to be statistical artifacts. His results indicate either that the Earth is as likely to suffer a major impact now as it was in the past, or that there has been a slight increase impact rate events over the past 250 million years.
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Blobrana


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Ancient scars

In 1965, researchers found 1,343 grams of iron meteorites some 3.9 km southwest of Wolfe Creek Crater, making it one of only five craters in Australia where meteorites have been found.
Meteorites only survive if the impact is small, producing a crater only a few hundreds of metres across. In larger impacts, the projectile is completely melted and vaporised. So, without the meteorite itself, what other than the circularity of such structures leads us to believe they were formed by impact?
The telltale evidence of a meteoritic origin falls into three main categories: structural, mineralogical and chemical. Geophysical surveys of many suspected impact structures show that they do not have deep-seated roots.
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Blobrana


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Evidence of Ancient Impact Preserved in Modern Sand

Through NAI's Minority Institution Research Support Program, scientists at the University of Puerto Rico and their collaborators have identified a unique record of an ancient meteorite impact event that is preserved in microstructures in detrital grains of quartz, zircon, and monazite in the Vaal River, South Africa. The sand samples were collected from the channel of the Vaal River near the two billion-year old Vredefort Dome impact structure, where impact-shocked minerals are known to occur in rocks.
This is the first report that impact shock-deformed minerals survive the process of uplift, erosion, and sedimentary transport. The unique mineral shock-deformation was documented by scanning electron microscopy at the University of Puerto Rico and the University of Wisconsin. The team's results are published in the current issue of the GSA Bulletin.
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Blobrana


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Research centre studies impact of meteor strikes

John Spray says most people have no idea Fredericton is home to a world-class research centre that studies the impact of meteor strikes on Earth.
Spray, the director of the Earth Impact Database based at the University of New Brunswick, says the centre houses the world's most detailed information on meteor impact sites.
Every day, researchers working in an unassuming office on the Fredericton campus field calls from people around the world who think they have stumbled on evidence of a meteorite slamming into the planet.
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General list of impact structures for google earth.

Impact structures (92kb, kmz)

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Blobrana


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Early stages of crater birth captured on camera

They move too fast for human eyes to see, but a camera has tracked individual sand particles spraying from an impact site in the first moments of crater formation.
Such movies could help us piece together the objects that created the craters which pock the surfaces of the moon and other celestial bodies. They could also help to predict the effects of impacts - to determine the risk flying debris poses to astronauts, for example.
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Blobrana


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A team of Canadian, Belgian and U.S. researchers is casting fresh doubt on one of the most contentious theories about this country's prehistory: that a massive meteorite strike around Hudson Bay some 13,000 years ago triggered the onset of a mini-ice age, the extinction of a host of "megafauna" species -- including the woolly mammoth -- and the collapse of the earliest wave of human settlement in the Americas.
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Blobrana


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The three largest impact craters on Earth are Vredefort (250 kilometres across), Sudbury (200 kilometres), and Chicxulub (170 kilometres). Most astronomers assume that these were created by asteroids roughly 10 kilometres across. But what of the possibility that comets may have been responsible for one or more of these impacts?

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