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Wannier, who is now retired, had been comparing biological debris in beach sands from different areas in an effort to gauge the health of local and regional marine ecosystems. The work involved examining each sand particle in a sample under a microscope, and with a fine brush, separating particles of interest from grains of sediment into a tray for further study.
"I had seen hundreds of beach samples from Southeast Asia, and I can immediately distinguish mineral grains from the particles created by animals or plants, so that's very easy," he said. In the Motoujina sands, collected by Wannier's colleague, Marc de Urreiztieta, he found familiar traces of single-celled organisms known as foraminifera, which come in a variety of forms. They typically have shells and reside in and around seafloor sediment.
Something - Samples - Particles - Particles - Spherule
"But there was something else ... it's so obvious when you look at the samples," he said. "You couldn't miss these extraneous particles. They are generally aerodynamic, glassy, rounded -- these particles immediately reminded me of some spherule (rounded) particles I had seen in sediment samples from the Cretaceous-Tertiary boundary," the so-called K-T boundary now referred to as the Cretaceous-Paleogene (K-Pg) boundary that marked a planetary mass extinction event, including the dinosaurs' die-off, about 66 million years ago.
In 1980, Luis Alvarez, a Nobel Laureate who worked at Lawrence Berkeley National Laboratory (Berkeley Lab) and UC Berkeley, together with his son, geologist Walter Alvarez, proposed a theory, based on a high concentration of iridium in deposits at the K-Pg boundary, that a large meteorite impact caused this massive die-off. Coupled with more recent evidence, scientists now believe that the impact occurred in the region of the Yucatan Peninsula. In meteorite impacts, liquified ground material is ejected into the atmosphere, forming droplets of glassy material that fall back to the ground.
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