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5 December 2013 11:26 am ,
Vol. 342 ,
Snake venoms are remarkably complex mixtures that can stun or kill prey within minutes. But more and more researchers...
At age 30, Dutch biologist Freek Vonk has built up a respectable career as a snake scientist. But in his home country,...
Since arriving on the island of Guam in the 1940s, the brown tree snake ( Boiga irregularis ) has extirpated native...
An animal rights group known as the Nonhuman Rights Project filed lawsuits in three New York courts this week in an...
Researchers have been hot on the trail of the elusive Denisovans, a type of ancient human known only by their DNA and...
Thousands of scientists in the Russian Academy of Sciences (RAS) are about to lose their jobs as a result of the...
Dyslexia, a learning disability that hinders reading, hasn't been associated with deficits in vision, hearing, or...
Exotic, elusive, and dangerous, snakes have fascinated humankind for millennia. They can be hard to find, yet their...
- 5 December 2013 11:26 am , Vol. 342 , #6163
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ScienceShot: The First-Known Comet to Strike Earth
11 October 2013 4:15 pm
A black, diamond-spackled pebble just a few centimeters across is the remainder of a comet that struck Earth almost 29 million years ago—making it the first direct evidence of a comet exploding in our atmosphere, scientists say. The stone, which the scientists named “Hypatia” after an Alexandrine mathematician and philosopher, was found in 1996 among tumbled bits of yellow sand glass (also known as the Libyan Desert Glass) scattered across tens of kilometers in southwestern Egypt, near the border with Libya. The glass itself, one large polished piece of which has a prominent place in a necklace that belonged to Egyptian pharaoh Tutankhamen, has been dated to 28.5 million years and has long been thought to be the result of a meteorite impact or an airburst caused by a comet breaking up in Earth’s atmosphere. To determine its origin, scientists performed a range of tests on the tiny pebble, examining its mineralogy, bulk chemistry, carbon isotope, and noble gas content. The stone’s noble gas content supports an extraterrestrial origin, while the presence of tiny diamonds—larger than nanodiamonds found in a common kind of meteorite called chondrites, but similar in size to diamond aggregates known to be formed by impacts—supports a cometary origin. The stone is also markedly carbon-rich, more so than other known extraterrestrial material aside from comets, the researchers will report in an upcoming issue of Earth and Planetary Science Letters. All of this, they say, points to a cometlike object entering Earth’s atmosphere, where it exploded, cooking the desert sand below to 2000°C and forming the Libyan Desert Glass.