Saturday, August 22, 2009

Where did the asteroid hit?

In 1990, Alan Hildebrand, a post- graduate from the University of Arizona, was put in touch will geophysicist Glen Penfield who worked for the major Mexican oil company Petroleos Mexicanos (PEMEX). Penfield believed that he had discovered a potential impact crater site. While looking over the old survey data from PEMEX for the Yucatán region of Mexico, Penfield noticed a huge buried arc of rock. He was excited to find that the 1960s gravity maps of the region revealed another arc, which fitted together with the first to form a huge circle. Deep beneath the little Mexican village of Puerto Chixulub at the tip of the Yucután peninsular, Penfield had found a crater over 100 miles wide, one of the largest impact structures on Earth.
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Penfield was aware that 50 years ago, PEMEX had been in the Yucután region looking for oil. Whilst digging an exploratory well, the workers had come across an unusual layer of igneous volcanic rock called andesite. Together, Hildebrand and Penfield re-examined the samples of andesite PEMEX had collected. Their analysis revealed that the rock contained shock- metamorphosized minerals, further evidence supporting their hypothesis that the Chixulub crater was the K-T impact site. The consensus of the scientific community is that this faded scar bears the mark of the most devastating impact the Earth has ever seen.
So it was 65 million years ago that a 2.6 billion ton asteroid the size of Mount Everest fell from the sky at 40,000 miles per hour. It slammed into the lagoons of New Mexico with the energy of 100 million megatons of dynamite, 200 times more powerful than the biggest nuclear bomb ever detonated on Earth.
A superheated shockwave rushed out from the impact faster than the speed of sound. The crash conjured ferocious fires and raised tsunamis around the Gulf of Mexico. The Earth trembled, volcanoes erupted and hurricane winds ripped through the air. Trillions of tons of debris were thrown up into the atmosphere, hurling down glowing fireballs on the Earth for hundreds of miles around.

The extinction event

Dinosaur fossil: why did dinosaurs become extinct?
The extinction event
In the 1970s, guess work turned into real scientific research thanks to a team at the University of California, Berkley. Geologist Walter Alvarez was examining rock strata in Guppio, Italy when he came across a layer of clay between the Cretaceous and Tertiary eras called the K-T boundary. The Cretaceous rock was full of fossils but rock from the Early Tertiary era had none. This brown-black stratum was formed at the time of the K-T mass extinction event that represented the end of the dinosaurs.
Alvarez took a handful of this K-T boundary clay to his father, the late Noble physicist Luis Alvarez, for analysis. With the help of nuclear chemists Helen Michels and Frank Asaro, they discovered that it contained an abnormally high quantity of the element iridium. This element is very rare in the crust of the Earth, but levels of iridium at the K-T boundary were 200 times higher than usual. Where had it come from? Extraterrestrial bodies such as comets and asteroids are rich in iridium, and to the Alvarez team, this clay bore the distinctive signature of asteroid dust. In 1980, Luis Alvarez and his son proposed that the dinosaur's demise was caused by an asteroid impact.
Since that time, geochemists have discovered iridium anomalies at the K-T boundary at over 100 places around the world. The boundary rock in these sites contains other unmistakable signs of a meteor impact. The scarred rocks show signs of being physically altered, fractured, melted and deformed beneath the intense heat and force of an explosion. For example, shocked minerals such as quartz are common in K-T boundary rock. These form under a sudden pulse of extremely high pressure. Small glass spherules are also present, remnants of superheated melt rock at the impact site, which were blasted as droplets that fell from the sky hundreds of miles around.
An asteroid that left its wounds around the world would have been huge. But where did it hit? The search for a crater site was on.

Death of the Dinosaurs

Dinosaurs dominated our planet for 160 million years. Now, all that remains of these huge creatures are bones. Fossil records show that 65 million years ago, something devastated the Earth's entire ecosystem and dinosaurs suddenly died out along with around 50% of all other species. But what caused their extinction? For many years, this question has remained a mystery shrouded in speculation.