What Killed the Dinosaurs?
Friday, March 22nd, 2013March 22, 2013
Scientists at the 44th Lunar and Planertary Science Conference (LPSC) held this week announced that the object that hit Earth 65 million years ago, leading to massive extinctions of species across the planet, may have been smaller than previously believed. Scientists have long thought that the object that impacted Earth was a huge, relatively slow-moving asteroid. This belief was based in part upon the stratum (layer) of Earth discovered by the American physicist Luis Alvarez and and his son, geologist Walter Alvarez. This layer, called the Cretaceous-Paleogene Boundary (at one time called the Cretaceous-Tertiary, or K-T boundary), contains a large amount of the chemical element iridium (Ir). The element is very rare in Earth’s crust but is common in such space bodies as asteroids and meteorites.
The iridium layer was not the only evidence that led scientists to think a large asteroid had struck Earth. There is also evidence of the impact. The Chicxulub crater in Mexico’s Yucatan Peninsula, is more than 112 miles (180 kilometers) in diameter and dates to the same geologic time period as the iridium layer; most scientists think the object that caused this crater is the object that spread a layer of iridium over the Earth and led to the extinction of the dinosaurs and many other animals and plants. Based on the level of iridium deposited and the size of the crater, scientists thought that only a large asteroid could have caused such an event.
Professor Jason Moore, a paleoecologist at Dartmouth College, presented findings at the 2013 conference showing that the geochemistry of the Chicxulub crater shows lower iridium levels than originally reported and lower levels than he believes could be created by a body as large as an asteroid. Dr. Moore believes that a body that could leave as little iridium and leave such a huge crater could not be a large asteroid. Moore believes the body that created the crater in Mexico was a small, fast-moving comet.
Comet or asteroid, the effect on the dinosaurs was devastating. Except, of course, for a group evolved from feathered dinosaurs that still does very well on Earth–the vertebrate class Aves, or birds.
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