Chicxulub Crater

http://en.wikipedia.org/wiki/Chicxulub_crater

Alan: I am surprised that the Chicxulub meteor was only six miles in diameter, creating a crater 112 miles wide. "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.'"

February 8, 2013

Scientists say they are a step closer to proving the death blow for dinosaurs 66 million years ago was a gigantic comet or asteroid that struck near Mexico

Although a catastrophic impact has long been thought to be involved earlier work left doubts about just when the object, estimated at some 10km in diameter, struck in relation to when dinosaurs disappeared.

But in a study published in the US journal Science, researchers used updated techniques to get a more precise date for the impact -- 66,038,000 million years ago -- which they said was accurate 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 who was not directly involved in the study.

The researchers also updated their estimate for the time the mass dinosaur extinction, and found that the date was within the same margin of error -- in other words, at around the same time as the asteroid impact.

'We have shown that these events are synchronous to within a gnat's eyebrow,' said Paul Renne, of the Berkeley Geochronology Centre at the University of California, Berkeley.

'The impact was clearly the final straw that pushed Earth past the tipping point,' he said.

But there were other factors as well, he said, including dramatic climate variation over the previous million years, which probably brought many species to the brink of extinction.

'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,' he said.

'The impact was the coup de grace.'

The dinosaur extinction -- which wiped out the large land-based behemoths as well as many ocean creatures -- was first linked to an asteroid or comet strike in 1980, by UC Berkeley professor Luis Alvarez and his son Walter.

The impact created a crater, now called Chicxulub, some 177km wide in the Caribbean, off the coast of Mexico.                                                               

"Dinosaur-Killer" Asteroid Crater Imaged for First Time National Geographic News March 7, 2003 A high-resolution map from NASA's Shuttle Radar Topography Mission (SRTM), released yesterday, has provided the most telling visible evidence to date of a 112-mile (180-kilometer) wide, 3,000-foot (900-meter) deep impact crater, the result of a collision with a giant comet or asteroid on one of Earth's all-time worst days. The existence of the impact crater, Chicxulub, was first proposed in 1980. In the 1990s, satellite data and ground studies allowed it to gain prominence among most scientists as the long sought-after "smoking gun" responsible for the demise of the dinosaurs and more than 70 percent of Earth's living species 65 million years ago. The relatively obscure feature is all but hidden in the flat limestone plateau of Mexico's Yucatán Peninsula. But using 3-D measurements of the Earth made with instruments on board an orbiting Space Shuttle, the remnants of the crater can now be seen clearly. "There are spectacular features that pop out in these maps as never before, and more subtle features, like Chicxulub, become apparent for the first time," said Michael Kobrick, SRTM project scientist at NASA's Jet Propulsion Laboratory (JPL), Pasadena, California. "In fact, much of the surface expression of Chicxulub is so subtle; if you walked across it you probably wouldn't notice it. That's where the view from space becomes invaluable, " Kobrick said. The Chicxulub data show a subtle, yet unmistakable, topographic indication of the impact crater's outer boundary: a semicircular trough 10 to 15 feet (3 to 5 meters) deep and 3 miles (5 kilometers) wide. Scientists believe the impact, centered off Yucatán's coast in the Caribbean, disturbed the subsurface rocks, making them unstable. The rocks were subsequently buried by limestone sediments, which erode easily. The crater rim's instability caused the limestone to fracture along the rim, forming the trough. Exactly how the Chicxulub impact caused Earth's mass extinctions is not known (see links below). Scientists imagine three possible scenarios: Some think the impact threw massive quantities of dust into the atmosphere which blocked the sun and arrested plant growth. Others believe sulfur released by the impact lead to global sulfuric acid clouds that blocked the sun and also fell as acid rain. Another possibility is that red-hot debris from the falling asteroid or comet triggered global wildfires. In February, NASA finished processing the SRTM mission's North America data set and delivered it to the National Imagery and Mapping Agency (NIMA). More than eight terabytes of data recorded aboard the Space Shuttle Endeavourwere refined into 200 billion research-quality measurements of Earth's landforms. NIMA will perform additional data finishing and send it to the U.S. Geological Survey's Earth Resources Observation Systems Data Center, Sioux Falls, South Dakota, for final archiving and distribution. Read More About Chicxulub: Researchers Rethink Dinosaur Die Off Scenario Fires From Asteroid May Have Spared Some Regions Could This Happen Again? Read: Is a Large Asteroid Headed for Impact With Earth in 2880? National Geographic Resources on Comets and Asteroids News Stories: NASA Should Lead Asteroid Defense, Group Says Comets: How Big A Threat To Earth? Surprise Comet Streaks Into Solar System NASA Practices Satellite Flyby of Asteroid Prehistoric Asteroid "Killed Everything" Unusually Well Preserved Crater Found in North Sea First Evidence for Early Meteorite Bombardment of Earth Fossil Leaves Suggest Asteroid Killed Dinosaurs U.S. Summons Experts to Draft Asteroid Defense Plan Comets May Have Led to Birth and Death of Dinosaur Era What Caused Argentina's Mystery Craters? Fighter Jet Hunts for "Vulcanoid" Asteroids Universe Reborn Endlessly in New Model of the Cosmos Chesapeake Bay Crater Offers Clues to Ancient Cataclysm Was Moon Born From Planet's Crash Into Earth? Mass Extinction That Led to Age of Dinosaurs Was Swift, Study Shows Interactive Features: Virtual Solar System Asteroids: Deadly Impact