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Stone Age The Stone Age marks a period of prehistory in which humans used primitive stone tools. He turned back to the block on his table and held a magnifying lens up to the tektite. Parallel, streaming lines were visible on its surface—Schlieren lines, formed by two types of molten glass swirling together as the blobs arced through the atmosphere.
Peering through the lens, DePalma picked away at the block with a dental probe. He soon exposed a section of pink, pearlescent shell, which had been pushed up against the sturgeon. Ammonites were marine mollusks that somewhat resemble the present-day nautilus, although they were more closely related to squid and octopi. As DePalma uncovered more of the shell, I watched its vibrant color fade. He stood up. He unwrapped a sixteen-inch fossil feather, and held it in his palms like a piece of Lalique glass.
When I encountered this damn thing, I immediately understood the importance of it. And now look at this. He pointed to a series of regular bumps on the bone. Now watch. Trapped inside were two impact particles—another landmark discovery, because the amber would have preserved their chemical composition. All other tektites found from the impact, exposed to the elements for millions of years, have chemically changed.
The bone was big for a Cretaceous mammal—three inches long—and almost complete, with a tooth. He believes that the jaw belonged to a marsupial that looked like a weasel.
The rest of the mammal remains in the burrow, to be researched later. At the bottom of the deposit, in a mixture of heavy gravel and tektites, DePalma identified the broken teeth and bones, including hatchling remains, of almost every dinosaur group known from Hell Creek, as well as pterosaur remains, which had previously been found only in layers far below the KT boundary. He found, intact, an unhatched egg containing an embryo—a fossil of immense research value.
The egg and the other remains suggested that dinosaurs and major reptiles were probably not staggering into extinction on that fateful day. In one fell swoop, DePalma may have solved the three-metre problem and filled in the gap in the fossil record. By the end of the field season, DePalma was convinced that the site had been created by an impact flood, but he lacked conclusive evidence that it was the KT impact.
It was possible that it resulted from another giant asteroid strike that occurred at around the same time. Deposits of Chicxulub tektites are rare; the best source, discovered in , is a small outcrop in Haiti, on a cliff above a road cut. In late January, , DePalma went there to gather tektites and sent them to an independent lab in Canada, along with tektites from his own site; the samples were analyzed at the same time, with the same equipment.
The results indicated a near-perfect geochemical match. The dinosaur feathers are crazy good, but the burrow makes your head reel. Jan Smit, a paleontologist at Vrije University, in Amsterdam, and a world authority on the KT impact, has been helping DePalma analyze his results, and, like Burnham and Walter Alvarez, he is a co-author of a scientific paper that DePalma is publishing about the site.
There are eight other co-authors. And this is the first time we see direct victims. In September of , DePalma gave a brief talk about the discovery at the annual meeting of the Geological Society of America, in Colorado. He mentioned only that he had found a deposit from a KT flood that had yielded glass droplets, shocked minerals, and fossils.
In the real Tanis, archeologists found an inscription in three writing systems, which, like the Rosetta stone, was crucial in translating ancient Egyptian. DePalma hopes that his Tanis site will help decipher what happened on the first day after the impact.
The talk, limited though it was, caused a stir. Some scientists were wary. He could have stumbled on something amazing, but he has a reputation for making a lot out of a little. Other paleontologists told me that they were leery of going on the record with criticisms of DePalma and his co-authors. All expressed a desire to see the final paper , which will be published next week, in the Proceedings of the National Academy of Sciences , so that they could evaluate the data for themselves.
After the G. The KT tsunami, even moving at more than a hundred miles an hour, would have taken many hours to travel the two thousand miles to the site. The rainfall of glass blobs, however, would have hit the area and stopped within about an hour after the impact. And yet the tektites fell into an active flood. The timing was all wrong. This was not a paleontological question; it was a problem of geophysics and sedimentology. Smit was a sedimentologist, and another researcher whom DePalma shared his data with, Mark Richards, now of the University of Washington, was a geophysicist.
At dinner one evening in Nagpur, India, where they were attending a conference, Smit and Richards talked about the problem, looked up a few papers, and later jotted down some rough calculations. One of them proposed that the wave might have been created by a curious phenomenon known as a seiche.
In large earthquakes, the shaking of the ground sometimes causes water in ponds, swimming pools, and bathtubs to slosh back and forth. Richards recalled that the Japanese earthquake produced bizarre, five-foot seiche waves in an absolutely calm Norwegian fjord thirty minutes after the quake, in a place unreachable by the tsunami. Richards had previously estimated that the worldwide earthquake generated by the KT impact could have been a thousand times stronger than the biggest earthquake ever experienced in human history.
Using that gauge, he calculated that potent seismic waves would have arrived at Tanis six minutes, ten minutes, and thirteen minutes after the impact. Different types of seismic waves travel at different speeds. The brutal shaking would have been enough to trigger a large seiche, and the first blobs of glass would have started to rain down seconds or minutes afterward.
The Tanis site, in short, did not span the first day of the impact: it probably recorded the first hour or so. This fact, if true, renders the site even more fabulous than previously thought. One day sixty-six million years ago, life on Earth almost came to a shattering end. The world that emerged after the impact was a much simpler place.
When sunlight finally broke through the haze, it illuminated a hellish landscape. The oceans were empty. The land was covered with drifting ash. The forests were charred stumps. The cold gave way to extreme heat as a greenhouse effect kicked in. Life mostly consisted of mats of algae and growths of fungus: for years after the impact, the Earth was covered with little other than ferns. Furtive, ratlike mammals lived in the gloomy understory. But eventually life emerged and blossomed again, in new forms.
The KT event continues to attract the interest of scientists in no small part because the ashen print it left on the planet is an existential reminder.
DePalma agreed. For the first hundred million years of their existence, before the asteroid struck, mammals scurried about the feet of the dinosaurs, amounting to little. In the next epoch, mammals underwent an explosion of adaptive radiation, evolving into a dazzling variety of forms, from tiny bats to gigantic titanotheres, from horses to whales, from fearsome creodonts to large-brained primates with hands that could grasp and minds that could see through time.
This is the last day of the Cretaceous. By Elizabeth Kolbert. By Paige Williams. Enter your e-mail address. Annals of Extinction. A Reporter at Large.
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