Because most rudists lived in the tropics, their die-offs give the impression that the K-T
catastrophe focused there, says Raup.
"I think people who have been supporters of Manson have realized that Manson is probably not responsible for virtually anything we see in the K-T
boundary sediments and that everything is fitting into place for Chicxulub:' says Joel D.
Since the late 1970s, geologists have found numerous signs of an extraterrestrial impact at the K-T
boundary, but until recently they had failed to locate the most important clue: a large crater of the right age.
When scientists from the University of California, Berkeley, began formulating the impact hypothesis back in the 1970s, they viewed the bolide strike as an event that would explain the well-known K-T
"I'm 99 percent sure that this is the K-T
boundary crater," Hildebrand told SCIENCE NEWS.
Researchers have discussed possible climatic implications of a huge meteorite strike at the K-T
boundary for a decade.
The cenotes add to a growing body of evidence pointing to the Yucatan structure as the K-T
In the same issue of NATURE, Jan Smith of the Free University in Armsterdam calls the Haitian fragments the "smoking gun" in the K-T
Shocked mineral grains, which scientists often view as telltale impact evidence, appear in many K-T
sites around the world, particularly in North America.
Berkeley researchers Luis and Walter Alvarez, Frank Asaro and Helen Michel proposed that the impact of a meteorite or comet sent up a global dust cloud that blocked out sunlight and caused a series of catastrophic changes that could explain the K-T
Bada examined a section of the K-T
boundary from Denmark in an effort to identify two of the most common meteoritic amino acids, isovaline and alpha-aminoisobutyric acid.
John McHone and his colleagues at Arizona State University in Tempe report in the March 3 SCIENCE that they have detected a mineral called stishovite in samples collected from the K-T
boundary at Raton, N.M.