Dinosaurs the Topic Must Be

Dinosaurs

The topic must be related to the asteroid theory of dinosaur destruction: Fossil and geological evidence

What killed the dinosaurs? This question has obsessed paleontologists and laypeople alike. One dramatic and popular theory is that a massive asteroid's collision with the earth was the source of the destruction of 65-70% of the entire planet's species, including the dinosaurs, 65 million years ago. A crater 112-mile-wide called Chicxulub was discovered in 1978 in Mexico's northern Yucatan that "suggested a massive extra-terrestrial impact" (New blow against dinosaur-killing asteroid theory, geologists find, 2009. National Science Foundation). Scientists discovered levels of iridium 30 times higher than normal around the layer of sedimentary rock laid down at the time of the dinosaur's extinction. The metal, while rare on Earth, is common in asteroids (Hypothesis: Asteroid impact, 2009, PBS). The impact of a giant asteroid may have created massive tsunamis and clouds of carbon gasses. The clouds would have blocked the sun's rays, rapidly cooling the earth to such an extreme many animals rapidly became extinct, including the cold-blooded dinosaurs. The greenhouse gases created by the impact may have then caused temperatures to skyrocket above pre-impact levels, again bringing death and destruction from temperature extremes to many more species (Hypothesis: Asteroid impact, 2009, PBS).

Yet researchers have found little evidence of massive, immediate species extinction in the Yucatan. Between four and nine meters of sediments were deposited at about two to three centimeters per thousand years after the impact. 52 species were present in sediments below the impact layer and the same 52 were still present in layers above. "The mass extinction level can be seen in the sediments [well] above this interval" (New blow against dinosaur-killing asteroid theory, geologists find, 2009. National Science Foundation). "Advocates of the Chicxulub impact theory suggest that the impact crater and the mass extinction event only appear far apart in the sedimentary record because of earthquake or tsunami disturbance that resulted from the impact of the asteroid (New blow against dinosaur-killing asteroid theory, geologists find, 2009, National Science Foundation). But the problem with the post-impact tsunami interpretation "is that this sandstone complex was not deposited over hours or days by a tsunami. Deposition occurred over a very long time period. The study found that the sediments separating the two events were characteristic of normal sedimentation, with burrows formed by creatures colonizing the ocean floor, erosion and transportation of sediments, and no evidence of structural disturbance" which means that there is no reason to believe that the asteroid impacted normal life in measurable fashion very quickly, or that fossil evidence of the asteroid's impact had been disrupted (New blow against dinosaur-killing asteroid theory, geologists find, 2009, National Science Foundation).