The geological and gravimetric (see above) evidence is compelling that this particular impact did severe damage to the earth's biosphere. Some paleontologists argue that dinosaurs were in a state of decline in speciation throughout the Cretaceous Era, and that the impact merely was the last straw. But as I understand what I have been reading, even this idea is under debate because of some recent fossil evidence that shows no real change in the number of dinosaur species all the way up to the stratum where evidence for the impact can be seen.
Because 65 million years had passed since the hypothetical impact, scientists decided to shift the search underground. A crater that old would almost certainly have been filled in. Just by chance, a Mexican oil company drilling off the coast of Yucatan discovered what appeared to be a crater about one kilometer (0.6 miles) under the surface near the village of Chicxulub. When core samples were analyzed, they showed the crater to be about 180 kilometers (112 miles) in diameter and 65 +/- 0.4 million years old.
As an astronomer, it is hard for me to comprehend that an object the size of the Yukatan Impactor traveling at 30 kilometers/sec, could not have had a devastating effect on the biosphere on a global scale. Unless the paleontologists have some conclusive evidence, I feel they might be quibbling over details. The 'dinosaurs' may have been in a state of decline for millions of years prior to the 'K-T Event' but this impact in the Yukatan would have had such a catastrophic global effect that it would surely have finished them off within a few weeks.
As for when the next one might occur, we know of thousands of objects in the kilometer size range. Fortunately they have stable orbits by most calculations. But there are many more undiscovered objects out there and most astronomers are certain from statistical inference, that many of them have 'earth' written on them. In my lifetime, I fully expect another 'Tunguska' event like the one in 1909. That will be more than sufficient to level New York City or Paris. These happen every 100 years or so, but like the San Francisco Earthquake, they can happen tomorrow, or in 30 years. That's statistics for you!
For more about the Chicxulub Impact Structure you can visit the Chicxulub Eseismic Experiment web page which was still on lime in May,2000. Note. Altavista searches under 'Chicxulub' seem to be more productive in finding information on this subject.
Copyright 1997 Dr. Sten Odenwald
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