There are still many scientists that believe an asteroid or comet (bit.ly/1XdMXqq), estimated at about 6 miles (10 kilometers) across, was to blame for the wipe out of the dinosaurs. Buried underneath the Yucatan Peninsula in Mexico, the Chicxulub (pronounced CHEEK-she-loob) crater is estimated to have created an initial hole 60 miles (100km) wide and more than 18 miles (30km) deep before collapsing to form a final crater more than 110 miles (180 km) wide and 12 miles (20 km) in depth.
Recently this theory has been challenged by more evidence researchers have been uncovering. A group of scientists led by Prof Gerta Keller of Princeton and Prof Wolfgang Stinnesbeck of the University of Karlsruhe found a series of geological clues in the rock formations where the iridium layer (bit.ly/1w9erCF) was separated from the spherule layer (bit.ly/1M9ymq0) by many meters of sandstone. They also found evidence of ancient worm borrows. In conclusion, the team theorize there must be a gap of some 300,000 years between the deposition of the spherules (from the crater) and the iridium (from the impact). The Chicxulub impact was too old therefore there had to have been two different impacts. That other crater has yet to be discovered.
In April, a $10 million drilling project will be constructed, sponsored by the International Ocean Discovery Program (IODP) and the International Continental Scientific Drilling Program, offshores in the Gulf of Mexico. Scientists and researchers will try to sink a diamond-tipped bit into the very center of this crater and retrieve rock cores that they hope will contain clues to novel microbial life and how ecosystems come back after such a tragedy. They also plan to drill into a circular ridge around the center of the crater's rim, called a "peak ring," to gain more information on how they form.
There are only two craters confirmed larger than Chicxulub that should also have peak rings: the 2-billion-year-old Vredefort crater in South Africa, and the 1.8-billion-year-old Sudbury crater in Canada. However, as University of Texas, Austin Sean Gulick, geophysicist and co-chief of this project says “Chicxulub is the only preserved structure with an intact peak ring that we can get to, all the other ones are either on another planet or they’ve been eroded.”
Although this is the first attempt at an offshore drilling, in the 1950s geologists for Pemex (Mexico’s national oil company) drilled several exploratory wells then lost interest when they found volcanic rocks instead of oil-bearing sediments. Then in 1991, Alan Hildebrand, a geologist at the University of Calgary in Canada, found quartz crystals shocked by an impact in the Pemex well core samples that had been sitting around for more than a decade. In 2005, a remote-sensing campaign, led by co–chief scientist Joanna Morgan of Imperial College London and Gulick, used small seismic explosions to illuminate the subterranean structures and pinpoint the best spot to reach the peak ring.
The researchers now are interested not only in the structure of the peak ring rocks but also what life they might host. Remote sensing has already suggested that the peak ring is less dense than expected for a granite - a sign that the rocks are porous and fractured in places. It is possible that these fractures, in the wake of the impact, were filled with hot fluids. They will count and culture any microbes found living in the fractures, and sequence their DNA. They could find genes showing that descendants of those that lived after the impact derive their energy not from carbon and oxygen, like most microbes, but from iron or sulfur deposited by the hot fluids percolating through the fractured rock.
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