In chapter four, Kolbert begins by showing the town of Gubbio. In this town, there is a narrow gorge, called the Gola del Bottaccione that has bands of limestone along its walls. Geologist Walter Alvarez discovered remnants of the famous asteroid that ended the cretaceous period in a layer of clay. He took a sample of this clay for further observation. Forams are shells that sink to the ocean floor after an animal died. They are used as index fossils which provides more information about dating. From the cretaceous period, the forams were large and abundant but above that layer, there were no forams. Alvarez usually believed in uniformitarianism, but this discrepancy made him think that this possibly happened suddenly. His father was a well known scientist and he brought the idea to use iridium to get more information about the clay, since they are abundant in asteroids. The layer of clay had an extreme amount of iridium in it. This led them to the conclusion that after an asteroid collided with the Earth, it released energy and debris that spread around the Earth which caused a mass extinction. This theory was heavily dismissed by other scientists who believed that extinction was a gradual process. Nevertheless, there was more proof that supported Alvarez’s theory. For example, the book states, “The first independent corroboration came in the form of tiny grains of rock known as ‘shocked quartz.’... In 1984, grains of shocked quartz were discovered in a layer of clay from the Cretaceous- Tertiary boundary in eastern Montana.” (80)
This chapter connects to the theme, The earth itself is one interconnected system. This is because the catastrophic asteroid that caused a mass extinction has effects that are found all around the world. Ammonites are extremely peculiar to scientists since they aren’t sure about how exactly they look but the sudden asteroid collision was too powerful to withstand and they went extinct. Ammonite fossils can be used in order to date certain fossils.
No comments:
Post a Comment