Scientists at the American Museum of Natural History and the University of Chicago have explained how a globe-encircling residue formed in the aftermath of the asteroid impact that triggered the extinction of the dinosaurs. The study, which will be published in the April issue of the journal Geology, draws the most detailed picture yet of the complicated chemistry of the fireball produced in the impact.
The residue consists of sand-sized droplets of hot liquid that condensed from the vapor cloud produced by an impacting asteroid 65 million years ago. Scientists have proposed three different origins for these droplets, which scientists call "spherules." Some researchers have theorized that atmospheric friction melted the droplets off the asteroid as it approached Earths surface. Still others suggested that the droplets splashed out of the Chicxulub impact crater off the coast of Mexicos Yucatan Peninsula following the asteroids collision with Earth.
But analyses conducted by Denton Ebel, Assistant Curator of Meteorites at the American Museum of Natural History, and Lawrence Grossman, Professor in Geophysical Sciences at the University of Chicago, provide new evidence for the third proposal. According to their research, the droplets must have condensed from the cooling vapor cloud that girdled the Earth following the impact. Ebel and Grossman base their conclusions on a study of spinel, a mineral rich in magnesium, iron and nickel contained within the droplets. "Their paper is an important advance in understanding how these impact spherules form," said Frank Kyte, adjunct associate professor of geochemistry at the University of California, Los Angeles. "It shows that the spinels can form within the impact plume, which some researchers argued was not possible."
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