"The Sixth Extinction" Chapter 4

In the late nineteen-seventies, Walter Alvarez, a geologist, uncovered the first pieces of evidence that an asteroid ended the Cretaceous period, thus causing the extinction of dinosaurs and many other species. The impact of the asteroid is located within a clay layer in Gubbio (KT boundary layer) that had been “gouged out by hundreds of fingers, a bit like the toes of the bronze St. Peter in Rome…” (Kolbert, 72) This metaphor helps to depict how despite the fact that this layer of clay has a lot of significance in the scientific world, it does not remain untouched nor undisturbed. This left me to wonder: Why exactly is this clay layer available to the public? Is it because many past scientists did not believe in the catastrophe of the asteroid that they had to make it visible to everyone?

The history of the world lies in the rocks and minerals found within the surface of the Earth because they contain fossils. For instance, forams are marine creatures that form calcite shells, which end up reaching the ocean floor once the animal that lives in those shells dies. Because forams are ubiquitously found, they are used as index fossils to determine the age of the rock it is found in. This is extremely helpful to scientists because they are able to compare what different limestones consist of, and determine if a type of fossil had disappeared within a layer of rock. If a particular fossil did not appear after a layer, this would mean that the group of organisms it belonged to disappeared. The controversy that comes with that is the manner in which that organism became extinct because many did not believe in the event that an asteroid hit the planet.

Walter Alvarez and his father, Luis Alvarez were distinguished scientists that set out to understand the components of limestone in terms of proving that the asteroid had indeed occurred. Iridium was used in this process because cosmic dust comes from meteorites and if there was more cosmic dust within the layer that was said to be from the Cretaceous period, then more iridium would be found there. When sampling layers of clay that were affected by meteorites, the results demonstrated abundant amounts of iridium. This helped to prove that the asteroid did hit the Earth, hence causing a mass extinction. However, many continued to not believe in the findings of Alvarez because they could not agree that a mass extinction was caused by an immediate event, or catastrophe. These opposing scientists argued that a mass extinction was a gradual process where the population of the organisms would decrease, making them rare, and then they would all die out.

This opposition to the Alvarez-extinction theory lessened overtime when new pieces of evidence were discovered. For example, a hundred-mile-wide crater was...rediscovered, beneath the Yucatan Peninsula.” (Kolbert, 80) This helped to back up the mass extinction theory because the Chicxulub crater could not be interpreted any other way. Its size was visible enough to anyone that the asteroid could have caused tremendous destruction, such as a mass extinction. At this point, people started to look at the evidence and they were gradually changing their minds and supporting Alvarez. Parallel to the extinction of the dinosaurs, Neil Landman discovered that during the same period, ammonites died out fairly quickly; once again proving that the asteroid and its cosmic dust resulted in a lot of damage and extinctions.