K-T Boundary Asteroid Event Sharply Tightened

To contact us Click HERE




What this means is that the errorhas been reduced by a full order of magnitude and this will now apply acrossmany other geological questions.  Mostsatisfying though is this result.  We allknow in our heart of hearts that the impact did it for the megafauna at the endof the cretaceous.  Yet a million yearerror bound does not make anyone brave. Now that we have narrowed it to 11000 years and it is still there tells us that it is almost impossible to have an alternative.
We will also now recover anaccurate global spectrum of associated geology with a clear idea of directassociations.  Recall most such processesactually last thousands of years to begin with. This is more than accurate enough.
It will still take years to playout but it is good to see it well begun with this question.
Asteroid Impact That Killed the Dinosaurs: New Evidence
By Charles Choi
http://news.yahoo.com/asteroid-impact-killed-dinosaurs-evidence-191146621.html
The idea that a cosmic impact ended the age of dinosaurs in what is nowMexiconow has fresh new support, researchers say.
The most recent and most familiar mass extinction is the onethat finished the reign of the dinosaurs — the end-Cretaceous orCretaceous-Tertiary extinction event, often known as K-T. The only survivorsamong the dinosaurs are the birds.
Currently, the main suspect behind this catastrophe is acosmic impact from an asteroid or comet, an idea first proposed by physicist Luis Alvarez and his son geologist Walter Alvarez. Scientists later found that signs of this collision seemed evident near the town of Chicxulub (CHEEK-sheh-loob) in Mexico in the form of a gargantuan crater more than 110 miles (180 kilometers) wide. The explosion, likely caused by an object about 6 miles (10 km) across, would have released as much energy as 100 trillion tons of TNT, more than a billion times more than the atom bombs that destroyed Hiroshima and Nagasaki.
However, further work suggested theChicxulub impact occurred either 300,000 years before or 180,000years after the end-Cretaceous mass extinction. As such, researchershave explored other possibilities, including other impact sites, such as the controversialShiva crater in India, or even massive volcanic eruptions, such asthose creating the Deccan Flats in India.
Timing of an impact
New findings using high-precision radiometric dating analysis of debriskicked up by the impact now suggest the K-T event and the Chicxulubcollision happened no more than 33,000 years apart. In radiometric dating,scientists estimate the ages of samples based on the relative proportions ofspecific radioactive materials within them.
"We've shown the impact and the mass extinction coincided as muchas one can possibly demonstrate with existing dating techniques,"researcher Paul Renne, a geochronologist and director of the BerkeleyGeochronology Center in California, told LiveScience.
"It's gratifying to see these results, for those of us who've beenarguing a long time that there was an impact at the time of this massextinction," geologist Walter Alvarez at the University of California atBerkeley, who did not participate in this study, told LiveScience. "Thisresearch is just a tour de force, a demonstration of really skillfulgeochronology to resolve time that well."
The fact the impact and mass extinction may have been virtuallysimultaneous in time supports the idea that the cosmic impact dealt the age ofdinosaurs its deathblow.
"The impact was clearly the final straw that pushedEarth past the tipping point," Renne said. "We have shown thatthese events are synchronous to within a gnat's eyebrow, and therefore, theimpact clearly played a major role in extinctions, but it probably wasn't justthe impact."
The new extinction date is precise to within 11,000 years.
"When I got started in the field, the error bars on these eventswere plus or minus a million years," added paleontologist William Clemensat the University of California at Berkeley, who did not participate in thisresearch. "It's an exciting time right now, a lot of which we canattribute to the work that Paul and his colleagues are doing in refining theprecision of the time scale with which we work."
Final blow
Although the cosmic impact and mass extinction coincided in time, Rennecautioned this does not mean the impact was the only cause of the die-offs. Forinstance, dramaticclimate swings in the preceding million years, including long coldsnaps in the general hothouse environment of the Cretaceous, probably broughtmany creatures to the brink of extinction. The volcanic eruptions behind theDeccan Traps might be one cause of these climate variations.
"These precursory phenomena made the global ecosystem much moresensitive to even relatively small triggers, so that what otherwise might havebeen a fairly minor effect shifted the ecosystem into a new state," Rennesaid.
The cosmic impact then proved the deathblow.
"What we really need to do is to understand better what was goingon before the impact — what was the level of ecological stress that existedthat allowed the impact to be the straw that broke the camel's back?"Renne said. "We also need better dates for the massive volcanism at the Deccan Flats to better understand when it first startedand how fast it occurred."
The scientists detailed their findings in the Feb. 8 issue of the journal Science.