Ken Bork, Ph.D., presented his lecture “The Day the Dinosaurs Died” at Yavapai College on Tuesday, Feb. 28, as part of their Osher Lifelong Learning Institute Brown Bag program.
Bork started his lecture by reminding the audience of Charles Darwin’s hypothesis that extinction is a key feature of organic evolution, as it opens up the path for diversification for species that fill ecological niches.
Most extinctions are slow and cumulative; however, the death of the dinosaurs was fast and cataclysmic.
Bork shared the work of physicist Luis Alvarez, Ph.D., and his Lawrence Berkeley National Laboratory team, who contributed to a scientific revolution in the 1980s. The geochemical evidence they found — an iridium spike found in rocks worldwide — pointed to an impact event. Although not a visible line, the iridium line clearly distinguished the Cretaceous–Paleogene boundary, or the periods before and after when the dinosaurs flourished.
Scientists and the public were slow to accept the idea of a rapid extinction, but Bork noted that bolide impacts are not as rare as we might think, showing the audience a graph with the locations of hundreds of craters worldwide, such as Meteor Crater near Holbrook, an excellent local example.
Current consensus is that the asteroid responsible for the extinction of the dinosaurs struck the Yucatan Peninsula in Mexico, forming the 124-mile-wide, 20- mile-deep Chicxulub crater, which was first described in 1991.
The asteroid involved was about seven miles in diameter, approximately the size of Mount Everest or Manhattan, and was traveling at a speed of 45,000 miles per hour. It most likely broke up while entering the earth’s atmosphere, as investigators taking core samples at 10-foot intervals down to 2,000 feet below the crater’s surface found evidence of shattered granite suggesting the asteroid was vaporized.
Bork also called the audience’s attention to the information preserved in microfossils, which he called “teeny clocks,” such as discoasters and foraminifera. These organisms were small enough that they were preserved during the impact. Investigators further found shocked quartz at the site, which is only formed during the intense pressures and temperatures of an impact event.
According to Bork, the collision released an amount of energy equivalent to 4.5 billion atomic bombs going off in one instant. The result was winds so powerful they blew down forests, triggered tsunamis worldwide, filled the atmosphere with soot, halted photosynthesis and acidified the oceans, leading in turn to a total ecosystem collapse.
On the first day following the impact, the atmosphere would have had a temperature of about 500 degrees Fahrenheit and the sky would have turned almost black from the injection of debris into the atmosphere.
Addressing the question of why some species survived the extinction, a concept known as differential extinction, Bork pointed out that those organisms that survived were decomposers and detritus consumers. Seeded plants also survived. Researchers estimate that full recovery of the planet’s ecosystems took between 4 million and 10 million years, although plankton recovered within a mere 30,000 years. Mammals continued to diversify during the period.
Bork finished by showing the audience a humorous diagram expressing how an individual’s knowledge of dinosaurs evolves during their lifetime. Dinosaur knowledge apparently peaks when they are 4 years old, declines when they get a paleontology degree and later peaks again when they have a 4-year-old of their own.
