Iridium is considered significant in the context of the dinosaur extinction primarily due to its association with the Cretaceous-Paleogene (K-Pg) boundary, which marks the end of the non-avian dinosaurs around 66 million years ago. The significance of iridium stems from the following points:
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Rare Element on Earth: Iridium is a rare metal on Earth's surface but is more abundant in asteroids and comets. Its presence in higher concentrations in certain geological layers suggested that an extraterrestrial event might have occurred.
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K-Pg Boundary Layer: Scientists discovered a distinct layer of clay rich in iridium at the K-Pg boundary, which was found in many locations around the world. This layer contrasts sharply with the sedimentary layers above and below it and provides physical evidence of a major event.
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Impact Hypothesis: The discovery of the iridium-rich layer supported the hypothesis that a large asteroid or comet impact was responsible for the mass extinction event that wiped out approximately 75% of Earth's species, including the non-avian dinosaurs. This idea was further reinforced by the identification of the Chicxulub crater in the Yucatán Peninsula, which dates to the same period.
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Mass Extinction and Environmental Changes: The hypothesis posits that the impact would have caused massive wildfires, tsunamis, and significant changes in the Earth's climate, leading to "nuclear winter" conditions. This drastic alteration of ecosystems would be detrimental to many species, including the dinosaurs.
In summary, the high levels of iridium found at the K-Pg boundary provide crucial evidence supporting the impact hypothesis for the mass extinction event, making iridium an important element in understanding the demise of the dinosaurs.
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