![]() The upshot of all that work, discussion, and scrutiny was that most lines of evidence seemed to be consistent with the asteroid hypothesis. The evidence relevant to each of these expectations is complex (each is a lesson in the nature of science on its own!) and involved the work of scientists all around the world. Thus, if the asteroid hypothesis were correct (and assuming that the crater was not subsequently destroyed by tectonic action), we would expect to find a gigantic crater somewhere on Earth dating to the end of the Cretaceous. Crater: If a huge asteroid had struck Earth at the end of the Cretaceous, it would have left behind a huge crater.Meteor Crater in Arizona does not date to the KT, but suggests the sort of land form that a massive asteroid would leave behind. Thus, if the asteroid hypothesis were correct, we would expect to find debris beds from tsunamis at the KT boundary. Tsunami debris: If a huge asteroid had struck one of Earth’s oceans at the end of the Cretaceous, it would have caused tsunamis, which would have scraped up sediments from the bottom of the ocean and deposited them elsewhere.Photo credit: Anja Scheffers & Dieter Kelletat. This tsunami-derived ridge of rubble in Portugal are not from the KT, but suggest the sort of tsunami debris we should expect to identify near the KT boundary. Thus, if the asteroid hypothesis is correct, we would expect to find evidence of these shockwaves (like telltale grains of quartz with deformations caused by the shock) at the KT boundary. Shockwaves: If a huge asteroid had struck Earth at the end of the Cretaceous, it would have generated powerful shockwaves.The two sets of planar lamellae in this quartz grain from the KT boundary in the Raton Basin, Colorado, are strong evidence of an impact origin. Thus, if the asteroid hypothesis were correct, we would expect to find glass from the impact at the KT boundary. Glass: If a huge asteroid had struck Earth at the end of the Cretaceous, it would have generated a lot of heat, melting rock into glass, and flinging glass particles away from the impact site.Greenish clay fragments in this KT rock from Belize were once glass shards. Thus, if the asteroid hypothesis were correct, we would expect to find particles from the impact site in the KT boundary layer. Impact debris: If a huge asteroid had struck Earth at the end of the Cretaceous, it would have flung off particles from the impact site.The orange wavy line seen in this wall of a Belize quarry marks the base of a KT debris flow that may have been caused by an asteroid impact. Thus, if the asteroid hypothesis were correct, we would expect to find many extinctions in the fossil record that line up exactly with the KT boundary, and fewer that occurred in the millions of years leading up to the end of the Cretaceous. Extinctions: If an asteroid impact had actually caused a global ecological disaster, it would have led to the sudden extinction of many different groups.The rightmost peak on this graph represents the spike in extinction rates at the KT boundary. In fact, the scientific community picked up the idea and ran with it, exploring many other lines of evidence, all relevant to the asteroid hypothesis. You might think that this would make the hypothesis impossible to test or that relevant evidence would be hard to come by. Scientists were confident that dinosaurs had gone extinct and were confident that a widespread iridium anomaly marked the KT boundary however, they vehemently debated the relationship between the two and the cause of the iridium anomaly.Īlvarez’s team hypothesized a specific cause for a one-time historical event that no one was around to directly observe.
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