What killed the dinosaurs?

According to a recent detailed study of melted impact sediments derived from the Chicxulub crater an ancient impact structure buried deep beneath Mexicos Yucatan peninsula an asteroid crash-landing 65 million years ago may have no connection with the dinosaurs abrupt demise. The popular killer asteroid theory was first proposed by father and son research team Luis and Walter Alvarez in the 1980s. Now a study conducted at the University of Utrecht in the Netherlands shows that the Chicxulub event apparently happened 300,000 years too early to be the smoking gun of the Cretaceous Period mass extinctions. A careful geochemical fingerprinting of natural glass spherules found in layers of sediments from northeast Mexico, Texas, Guatemala, Belize, and Haiti all point back to Chicxulub as their source. But our analysis places the impact at about 300,000 years before the infamous extinctions marking the boundary between the Cretaceous and Tertiary periods the K-T boundary layer, said Dr. Markus Harting of the University of Utrecht. The K-T boundary contains large amounts of the metal iridium. Meteors and asteroids contain a higher percentage of iridium than the crust of the Earth. Harting skillfully employed electron microscopy to discover that Chicxulub impact glass spherules were reworked by erosion; the spherules migrated, thanks again to Mother Nature, close to the K-T boundary. Its akin to a flood moving ballistic evidence from a murder scene meters away from the scene of the crime. Investigators will read the reworked evidence and draw false conclusions about how and where the crime occurred. The sediments are offering clues as to what happened during the 300,000 years between the Chicxulub impact event and the K-T boundary die-offs in short, nothing happened, said Harting. The K-T iridium layer belongs to a totally different event. If the Chicxulub impact didnt cause the K-T iridium layer, what did? One possibility, said Harting, is that Earth and perhaps the entire solar system passed through a thick cloud of cosmic dust 65 million years ago. Did Hartings hypothetical cosmic cloud kill off the dinos? You probably have a time when lots of meteorites are coming down and never touching the ground, said Harting. Instead they burned up as shooting stars, depositing their iridium in the atmosphere. There it was quickly rained out, washed into lakes and oceans and buried in contemporary sediments. Models of the Chicxulub impact depend on the so-called nuclear winter scenario, in which the Earth, smothered by gaseous and particulate impact debris, cooled off dramatically. First, the Cretaceouss forests died off, then it was the land animals turn. Yet sun-loving animals like crocodiles and turtles appear to have glided right through without any ill effects, Harting said. According to geologist Ann Cairns of the Geological Society of America, Hartings evidence is perhaps the silver lining to Chicxulub's fall from the status of most-massive-of-all-murderers: Even giant impacts aren't necessarily global catastrophes. Whats in the sky: Planets are front and center in the night sky this month. Mars and Saturn are close together for most of the month; look low in the west in early evening. Lou Varricchio, M.Sc., lives in Vermont. A former NASA science writer, he is a community journalist and Vermonts NASA/JPL solar system ambassador.

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