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New Evidence Comet Or Asteroid Impact Was Last Straw For Dinosaurs

February 7, 2013
Image Credit: sdecoret / Shutterstock

Alan McStravick for redOrbit.com — Your Universe Online

We´ve had an increasing fascination with comets and asteroids over the past several years. We´ve fictionally sent a rogue group of astronauts to detonate one of these heavenly travelers. We´ve seen the disastrous effect of a potential impact in both movies and on television. We´ve elevated our global anxiety tracking the trajectory of these large, quickly moving celestial bodies. And it seems our vigilance on this matter, with the publishing of a new study, is well founded. In fact, just this month there’s a small asteroid called 2012 DA14 that will come within 17,200 miles of Earth.

Scientists from the Berkeley Geochronology Center (BCG), the University of California, Berkeley, and universities in the UK and the Netherlands have winnowed the precision of the dates regarding the extinction of the dinosaur and the well-known impact that occurred around the same time. Prior to this study, there was a fair amount of skepticism as to whether or not the impact actually had a direct effect on the global mass extinction.

Paul Renne, BGC director and UC Berkeley professor in residence of earth and planetary science, in relating his personal interest in this matter, stated in an e-mail to ABC News, “I wouldn’t say the theory was in trouble, but there have been skeptics and the absolute timing has never quite lined up.”

In fact, the researchers claim the two dates are so close it is now believed the comet or asteroid impact, if not solely responsible for the mass global extinction, was definitely the final nail in the coffin for the existence of the dinosaurs.

“The impact was clearly the final straw that pushed Earth past the tipping point,” said Renne. “We have shown that these events are synchronous to within a gnat´s eyebrow, and therefore the impact clearly played a major role in extinctions, but it probably wasn´t just the impact.”

The impact Renne mentions refers to the Chicxulub crater, located just off the Yucatan coast of Mexico. This 110-mile-wide crater is thought to have been carved into the Earth by an object some six miles across. Chicxulub was first linked to the possible extinction of dinosaurs in 1980 by the late UC Berkeley Nobel Laureate Luis Alvarez and his son, Walter, who is, himself, a UC Berkeley professor emeritus of earth and planetary science. As a result of the impact, debris was cast into the atmosphere. This debris, consisting of tektites, shocked quartz and iridium-enriched dust, can still, to this day, be found around the globe.

Renne and colleagues, in establishing a revision for the dates associated with the impact and mass extinction, have claimed definitively that Chicxulub was formed 66,038,000 years ago. This new date is, within error limits, effectively the same as the date of extinction. The two events are, according to Renne, simultaneous. Their findings, published in tomorrow´s issue of the journal Science, is the culmination of a three year long study to rectify the historical dating of the two events to within error limits.

The method the team employed to bring a more correct dating in-line, known as the argon-argon technique, was initially recalibrated and improved by the researchers. One of the first collection sites, the Hell Creek area in Montana, yielded volcanic ash that was analyzed with the recalibrated argon-argon technique. These collections were important for helping to determine the date of the mass extinction. Hell Creek, located below the extinction horizon, is an excellent source of many dinosaur fossils from both before and after the extinction.

Also collected were tektites from Haiti. Using the same argon-argon technique, these samples were used to determine how long ago the impact in the Caribbean occurred. It was determined, after both site samples were analyzed, the extinction and impact dates are precise to within 11,000 years.

“When I got started in the field, the error bars on these events were plus or minus a million years,” said paleontologist William Clemens, a UC Berkeley professor emeritus of integrative biology who has led research in the Hell Creek area for more than 30 years, but was not directly involved in the study. “It´s an exciting time right now, a lot of which we can attribute to the work that Paul and his colleagues are doing in refining the precision of the time scale with which we work. This allows us to integrate what we see from the fossil record with data on climate change and changes in flora and fauna that we see around us today.”

Even though the impact and extinction dates are basically the equivalent of a blip in geologic time, Renne cautions this doesn´t mean the impact was the sole cause of the mass extinction. Instead, he claims climate variation over a million year period, which included prolonged cold snaps within the Cretaceous hothouse environment, likely brought many creatures right up to the brink of extinction. The team´s contention is the impact likely kicked many of these animals over the edge.

“These precursory phenomena made the global ecosystem much more sensitive to even relatively small triggers, so that what otherwise might have been a fairly minor effect shifted the ecosystem into a new state,” Renne said. “The impact was the coup de grace.

“It’s possible that the impact was enough, but there is ample evidence that other things such as rapid climate swings were going on just beforehand, so it seems likely that the impact tipped the balance of an already-stressed biosphere,” he continued. “I’ve always felt that we should avoid simply saying, ‘OK, Eureka, it was an impact and now we’re done’ — simple answers are often incomplete.”

Up next for Renne and his team is the exploration of other terrestrial phenomena that may have also played a role in the near total global extinction. In particular, a series of Indian volcanic eruptions produced the extensive Deccan Traps. The volcanic rocks will soon receive Renne´s attention as he hopes to re-date the rocks. This re-dating will aid in presenting them with a more precise measure of the overall duration of the eruptions and their space in time with relation to the dinosaur extinction.

“This study shows the power of high precision geochronology,” said coauthor Darren F. Mark of the Scottish Universities Environmental Research Center, who conducted independent argon-argon analyses on samples provided by Renne. “Many people think precision is just about adding another decimal place to a number. But it´s far more exciting than that. It´s more like getting a sharper lens on a camera. It allows us to dissect the geological record at greater resolution and piece together the sequence of Earth history.”

The work was supported by the Ann and Gordon Getty Foundation, UC Berkeley´s Esper S. Larsen Jr. Fund and the National Science Foundation.


Source: Alan McStravick for redOrbit.com – Your Universe Online



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