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Asteroid Impact Tied to Rise of Dinosaurs

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Derek
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« on: June 23, 2007, 03:24:14 am »

Asteroid Impact Tied to Rise of Dinosaurs
By Robert Roy Britt
Senior Science Writer
posted: 02:00 pm ET
16 May 2002



 

The history of dinosaurs and asteroids became further entwined today with the announcement that an impact from a space rock 200 million years ago may have eliminated some competition and helped the giant reptiles flourish and eventually dominate the planet.

Scientists have long suspected that an asteroid led to the demise of dinosaurs' 65 million years ago. Research last year suggested that an earlier impact 251 million years ago might have allowed dinosaurs to evolve in the first place.

Now a new study of more than 70 sites in North America finds evidence that the well-documented mass extinction 200 million years ago was also caused when an asteroid or possibly a comet hit Earth. Within 100,000 years of the event -- an evolutionary eyeblink -- dinosaurs radiated and multiplied swiftly, reaching their historical maximum diversity in the region.

They went on to dominate the planet for 135 million years.

The findings are based on footprints, bones, fern spores, and the discovery of elevated levels of iridium -- a rare element on Earth but one common among space objects. The results help build a sometimes controversial case that in the grand scheme of terrestrial time, space rocks frequently snuff out entire species while simultaneously breathing fresh life into the evolutionary process.

The results, which need to be validated by further research, will be published in the May 17 issue of the journal Science.

Rocky times

Researchers have thought for more than a decade, and with growing certainty, that an impact played a critical role in the ultimate death of dinosaurs. Other species perished, too, in an event that allowed mammals to prosper in a world where there were fewer large creatures to step on them or swallow them whole.

However only in recent years has evidence turned up linking earlier mass extinctions to impacts.

The new research documents a widespread die-off that occurred at the boundary of the Triassic and Jurassic periods in time, when dinosaurs had begun to gain a foothold in what is now North America. The study found iridium in layers of rock in Earth's crust at several sites that have been traced back to the same point in time.

The element is prevalent in asteroids and comets and can be left behind as a global signature when an incoming object vaporizes on impact and kicks up a dust storm that circles the planet.

Though there is no evidence of a crater, the iridium "creates a time marker for comet or asteroid impacts," said Dennis V. Kent, a Rutgers University geologist and part of the research team. "Correlating the finds with evidence of plant and animal life helps to tell us what happened."

Paul E. Olsen of the Lamont-Doherty Earth Observatory of Columbia University led the study.

Asteroid or volcanism?

An asteroid could certainly do the trick, experts say, creating years of winter-like conditions caused by tons of dust that blots out the Sun.

Yet, other researchers have speculated that the extinction 200 million years ago was instead a result of increased volcanic activity, which would have pumped choking chemicals into the atmosphere. Some experts say a combination of an impact and increased volcanism might provide a one-two punch necessary to cause extinctions of many species.

Either way, the case is not firm.

"Considerably more geochemistry is needed to rule out a volcanic origin," Olsen told SPACE.com. "And much more sampling over a broader temporal and geographic range is needed to confirm that what we found is really a global event tied to an impact."

Olsen said, however, that the team found iridium at levels two and three times higher than normal "background" levels found in sedimentary rock. This anomaly, or difference in levels, is not as high as has been documented for the so-called K-T impact that occurred 65 million years ago (and for which a crater exists).

"The magnitude of our anomaly is small compared with that at the K-T boundary, but it is similar to anomalies at other known impacts," Olsen said.

The iridium spike was found to be coincident with a spike in fern spores, thought to be a signal of recovery from an impact.

Paul Sereno, the noted dinosaur hunter from the University of Chicago, said the study provides "critical new data on the origins and early evolution of dinosaurs that support a sharp break in the fossil record between the early and rarer dinosaurs of the Triassic period, and the larger dominant dinosaurs of the early Jurassic."

The number and extent of the Triassic-Jurassic extinctions have been much debated.

"Which is why this well-dated, well-supported find of iridium and a fern pollen spike in association with footprints is such key new information," Sereno told SPACE.com. "Doubtless it will spark new research into the question of how and when dinosaurs rose to dominance on land -- a question that may ultimately become as resolved as the events at the end to the dinosaur era."

Next Page: Other impacts, and how this study was done

http://www.space.com/scienceastronomy/planetearth/jersey_dinosaurs_020516-1.html
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Derek
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« Reply #1 on: June 23, 2007, 03:25:23 am »

Other possible impacts

A study last June, also reported in Science, found extraterrestrial gases trapped inside special molecules, known as fullerenes, in rock layers corresponding to an earlier and greater mass extinction, which occurred 251 million years ago. This event wiped out 75 percent of all species and was likely a first step in allowing dinosaurs to enter the scene.

One of the researchers involved with that study, Robert Poreda of the University of Rochester, said the newer results need to be interpreted with caution.

"Iridium can be an important tracer for studying impacts, but in some ways the overwhelming signal observed at the K-T site has caused some to view it as a sort of 'key' signal," Poreda said. "At two to three times the background signal [as in Olsen's study] the case can be made for a non-impact scenario."

The elevated iridium, Poreda said, might reflect changes in sedimentation or accumulation rates where no impact occurred. He said several indicators need to coincide, from iridium results to fullerenes, shocked quartz structures and more.

Nevertheless, Poreda said the new research "represents one of the first steps" in showing that the Triassic-Jurassic extinction was caused by a space rock. His own feeling, he said, is that a few years of study will show that to be the case.

How it was done

The new iridium study used a special technique called iridium coincidence spectrometry, which finds the element based on the ejection of two gamma-ray particles per atom after they have been irradiated in a nuclear reactor, to make fine comparisons of iridium in the sediment layer compared to older and newer layers.

Christian Koeberl of the University of Vienna performed the work.

Earlier attempts to find an iridium "spike" in the Triassic-Jurassic boundary did not succeed because the spectrometry equipment was not sensitive enough, the researchers said.

The work is painstaking. Earth was an entirely different place 200 million years ago, with all the continents crowded into a single land mass called Pangea. Researchers must first locate exposed sedimentary layers, which may have been folded under and back out to the surface over the eons, and then properly date and sample them.

Much of the evidence was collected in what are now parts of New Jersey and Pennsylvania, along with other dig sites dotting the eastern United States.

http://www.space.com/scienceastronomy/planetearth/jersey_dinosaurs_020516-2.html
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« Reply #2 on: June 23, 2007, 03:28:12 am »

Mass Extinction & Rise of Dinosaurs Tied to Cosmic Collision
By Robert Roy Britt
Senior Science Writer
posted: 02:00 pm ET
22 February 2001


 

For dinosaurs, the beginning seems to have been as violent as the end, based on new research that puts the blame for the worst mass extinction in history, 251 million years ago, squarely on the shoulders of a huge space rock.

The discovery also suggests that civilizations have fairly fixed periods during which to gain the intelligence needed to avoid being wiped off the face of the Earth. Or wherever.

Scientists have known for about a decade that a massive object, probably an asteroid, slammed into Earth 65 million years ago, presaging the demise of the dinosaurs and the rise of mammals. There is a crater in Mexico to prove it, as well as heavy concentrations of iridium -- a signature of asteroids -- spread around the world in soil dated to that time.

But 251 million years ago, before dinosaurs existed, the worst extinction ever recorded left the planet nearly bereft of plants and animals: More than three-fourths of all species perished, leaving a layer of fossils worldwide as a record. With evolution's slate relatively clean, the door was wide open for new species to take over. Lizards leapt at the opportunity, evolving into dinosaurs within just a few million years.

251 million-year-old mystery

But what triggered this earlier extinction? Researchers have speculated that it might have been an asteroid or comet impact, like the later event that did in the dinos. Or, they have ventured, it could have just been heavy volcanic activity or extreme climate change. But until now, there has been no clear evidence.

Here's why: Earth has changed drastically in the intervening 251 million years. Back then, all the continents were huddled together in one giant landmass, called Pangaea. If there were an impact, the resulting crater would long since have been split apart or folded into the planet's crust.


And despite a thorough search, no increased levels of iridium have been associated with that time. So researchers have been looking for other evidence of an impact.

And now they seem to have found it. The new study, announced today, uncovered extraterrestrial gases trapped inside special molecules, known as Buckyballs, in ancient soil layers. Scientists say the evidence points to a colossal whack from a comet or asteroid roughly 3.7 to 7.5 miles (6 to 12 kilometers) wide -- about the same size as the one that ultimately destroyed most dinosaurs 186 million years later.

"These two extinctions are like bookends for the age of the dinosaurs," said Robert Poreda, a University of Rochester scientist who worked on the study. Full results are in the Feb. 23 issue of the journal Science.

Rise of intelligent civilization(s)

In the past 500 million years, there have been about five giant extinction events, researchers say. The new finding means that at least two of them were caused by impacts. The others also may have been.

"This suggests that the evolution of life on Earth is strongly coupled with our cosmic environment," said Christopher Chyba, a SETI Institute researcher who was not directly involved in the study. The new work even has implications for the origin of intelligence on Earth, and possibly elsewhere, Chyba said. It hints at the possibility that Earth's biosphere is regularly disrupted, every 100 million years or so, by giant impacts that would render human life impossible.

"We ourselves would truly not have been here [if not for] the extinction that eliminated the dinosaurs," Chyba said at a news conference at NASA Headquarters. "A biosphere only has a certain amount of time to develop a technical intelligence which is capable of realizing that there is an impact hazard, cataloging that hazard and...avoiding the next impact."

Bottom line: Only a civilization smart enough to spot the hazard and mitigate it can survive.

Chyba said that because other planets around other stars would likely face the same risks, the next logical thought is that any potential intelligent ET would also have to be quick-witted to avoid going the way of the dinosaurs. He said this might "increase the likelihood of technical civilizations."

"Not a pretty picture for life"

Because Earth's crust has stretched and folded so dramatically in the past 251 million years, the researchers say there is no way to pinpoint where the space rock hit. But they can guess at the wild events that followed.

Earthquakes and volcanoes would have rattled the planet, explains the University of Washington's Luann Becker, lead author of a study. Lava poured out in volume -- enough to cover the planet 10 feet (3 meters) deep. The oceans dropped 820 feet (250 meters).

Worse, the combined effects of the object vaporizing on impact, along with all the volcanism, poisoned what was left of the seas and choked the air with ash and deadly gases. Sunlight may have disappeared for months. Or, Becker and her colleagues say, carbon dioxide may have trapped the Sun's energy and sent temperatures soaring.

Either way, it was "not a pretty picture for life, which is why it's the greatest of all mass extinctions recorded on Earth," Becker told SPACE.com.

Some 90 percent of all sea life perished, along with 70 percent of land animals and most terrestrial plants.

The researchers say the volcanic activity was likely going on before the impact, but was then fueled into a frenzy. The one-two punch, it seems, may be what's needed to precipitate the worst extinctions. Poreda called the whole scenario a "blast from the double-barreled shotgun."

The discovery, and the new technique used to make it, could lead scientists to find that some of the other 20 or so mass extinctions in the last billion years were also caused, or at least helped along, by cosmic collisions.

Next page: ET Buckyballs left as a calling card

http://www.space.com/scienceastronomy/planetearth/impact_extinction_010222-1.html
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« Reply #3 on: June 23, 2007, 03:30:23 am »

Calling card: ET Buckyballs

The key to the new finding lay inside odd molecules known as Buckyballs, which scientists describe as looking somewhat like tiny soccer balls.

Buckyballs are complex carbon molecules more scientifically known as fullerenes. They are named after Buckminster Fuller, who invented the geodesic dome (which also looks like a soccer ball). Buckyballs have a unique characteristic: They can trap helium and argon gas inside their cage-like structures.


The research team studied Buckyballs found in exposed soil layers known to be 251 million years old, from sites in China and Japan. Inside these fullerenes, the scientists found gases with a particular structure that could not have formed in our solar system. So these molecules are not only from beyond Earth, but from beyond our solar system, having formed in some distant primordial environment unlike the one created by our Sun. They would have then been incorporated into a comet when our solar system formed.


Death of the Dinos
Beginning in the 1980s, researchers found evidence that a giant impact caused a mass species die-off 65 million years ago, known as the Cretaceous-Tertiary extinction, that led to the demise of most dinosaurs. In 65 million-year-old soil around the world, researchers found up to 100 times the amount of iridium -- a signature of asteroids and comets -- than what occurs normally.

Later, a 120-mile- (200-kilometer-) wide crater was found mostly buried under eons of sediment in Mexico"s Yucatan Peninsula, near the village of Chicxulub. Aerial photographs reveal only a hint of the crater"s rim. Learn more.


Scientists say the object that slammed into Earth 251 million years ago, which may have been a comet, likely had a different composition than the presumed asteroid that hit the Yucatan Peninsula 65 million years ago, and hence left behind only small quantities of iridium. Comets travel at greater speeds, and if it were a comet, it may have been on the small end of the size estimate in the report. A small, fast-moving comet could generate the same destruction as a larger, slower asteroid.

Quick end

Researchers suspect that the Permian-Triassic Boundary event, as the 251 million-year-old extinction is known, happened very quickly. Previous fossil evidence has shown a sharp reduction in the number of certain species at the boundary between the Permian and Triassic periods in history. The entire die-off is thought to have taken place in less than 100,000 years.

"That's a microsecond in geologic time," Becker said. She and her colleagues say the newly proposed scenario, in which species would have toppled one after the other going up the food chain, fits that short time frame.

Becker and her colleagues plan to apply the new technique to other known mass extinctions, including one in the Devonian period, 364 million years ago, and another at the end of the Jurassic period roughly 200 million years ago. This latter event coincided with the breakup of Pangaea and the birth of the Atlantic Ocean.

Death and life

Scientists say the new discovery, funded by NASA and the National Science Foundation, is further evidence that comets and asteroids are both killers and master chefs in the grand recipe of life. Comets may have delivered the water that transformed a dry early Earth into a watery orb, and comets and asteroids both have been found to pack some of the molecules needed to seed life.

The field of astrobiology has burgeoned in recent years as researchers scramble to confirm whether life on Earth originally came from space.

Meanwhile, the findings should not change our view of the potential fragility of our own species, said Theodore Bunch, a geologist at NASA's Ames Research Center in California who also worked on the study. Estimates of potentially devastating impacts have already been worked out based on other factors, Bunch said, including impact evidence on the Moon and Mars, which preserve craters better than Earth.

Asteroids or comets big enough to cause global destruction are estimated to come around every 100 million years or so. Smaller space rocks -- still big enough to destroy a city or generate a deadly tsunami in the ocean -- are thought to hit the planet every 1,000 to 10,000 years.

The most recent scare was the Tunguska event in 1908, which flattened some 1,200 square miles (3,108 square kilometers) of Siberian forest. The suspected asteroid involved was never found -- it didn't even reach the ground. The object, thought to be about 60 yards (55 meters) wide as it sped into Earth's atmosphere, exploded 3 or 4 miles (5 kilometers) from the surface, experts now believe.

The explosion was like several tons of TNT. It broke windows and knocked people to the ground 37 miles (60 kilometers) away in the sparsely populated area, says William K. Hartmann of the Planetary Science Institute in Tucson, Arizona. A fiery cloud was seen up to a distance of 300 miles (500 kilometers), where witnesses reported hearing "deafening bangs." The explosion sent a rush of hot wind that felled and burned the trees.

Chyba, of the SETI Institute, said there's no need to panic, and no need right now to spend money to defend Earth against any potential species-ending impact.

"Even if one of these objects is likely to hit Earth [anytime soon], and that's very unlikely, we would almost certainly have decades, if not centuries, to go before that impact would happen," Chyba said. "So we'd have a long time to think about what to do about it."

Meanwhile, researchers are working to catalogue asteroids and comets that could pose a threat. Of the 1,000 or so expected to exist, each more than a kilometer wide, about 400 have been found. Chyba said 90 percent of them should be detected by the year 2015.

http://www.space.com/scienceastronomy/planetearth/impact_extinction_010222-2.html
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