In 1956, Russian astronomer Joseph Shklovsky (1916-85) became the first scientist to consider the extinction was due to a single catastrophic event when he theorized that a supernova (the explosion of a dying star) showered the earth in radiation that could have killed the dinosaurs. Once again, the problem with the theory was explaining why dinosaurs died out and other species did not. Also, scientists said that such an event would have left evidence on the surface of the earth–trace amounts of radiation dating back to the Cretaceous Period. None was found.
Enter Luis Alvarez, a Nobel Prize-winning physicist, inventor and pioneer in the field of radiation and nuclear research. He and his son, noted geologist Walter Alvarez, were conducting research in Italy when they discovered a centimeter-thick layer of iridium-enriched clay at the K-T boundary. Iridium is rare on earth, but more common in space. The Alvarezes published their findings in 1981, postulating that the thin layer of iridium was deposited following the impact of a large meteor, comet or asteroid with the earth. Furthermore, this bolide impact (the meteor, comet or asteroid colliding with the earth’s surface) could have caused the extinction of the dinosaurs. At the time, the Alvarez theory was so far removed from prevailing hypotheses that it was ridiculed. Slowly, though, other scientists began finding iridium evidence at various places around the globe that corroborated the Alvarez theory. There was, however, no smoking gun in the form of an impact site.
Then in 1991, a massive meteor crater 110 miles in diameter was discovered on the edge of the Yucatán Peninsula, extending into the Gulf of Mexico. The Chicxulub Crater, as it was dubbed, was named for a nearby village. Scientists believe the bolide that formed it was roughly 6 miles in diameter, struck the earth at 40,000 miles per hour and released 2 million times more energy than the most powerful nuclear bomb ever detonated. The heat would have broiled the earth’s surface, ignited wildfires worldwide and plunged the planet into darkness as debris clouded the atmosphere. Miles-high tsunamis would have washed over the continents, drowning many forms of life. Shock waves would have triggered earthquakes and volcanic eruptions.
The resulting darkness could have lasted for months, possibly years. It would have plunged the earth’s temperatures into the freezing zone, killing plants and leaving herbivores with nothing to eat. Many dinosaurs would have died within weeks. The carnivores who feasted on the herbivores would have died a month or two later. Overall, the loss of biodiversity would have been tremendous. Only small scavenging mammals that could burrow into the ground and eat whatever remained would have survived. The iridium layer plus the Chicxulub Crater were evidence enough to convince many scientists that the bolide impact theory was credible. It explained much of what previous theories could not.