Chapter 4 - Admir Basic

In Chapter 4 of The Sixth Extinction, Elizabeth Kolbert opens up the chapter with the small town of Gubbio. This was the town in which geologist Walter Alvarez discovered traces of an asteroid that future scientists believed hit the Earth during the Cretaceous Period. Walter was advised by his father, Luis Alvarez to record information on the clay layers for iridium in order to find out where the clay originated from and to use radioactive dating. The clay was found with enormous amounts of iridium that was dated all the way back to the Cretaceous Period. They argued that an asteroid hit the planet at the end of the Cretaceous Period killing the dinosaurs. Many scientists disagreed with their theory of mass-extinction until it proved to be a viable explanation for the fossil gap. It explains the richness of iridium in the clay layers and why there was a huge gap in time for the fossil record. The author meets with Neil Landman who shows her a fossil site filled with ammonite fossils and rocks rich in iridium. He explained that during the Cretaceous Period, ammonites were wiped out by the mass extinction while nautiluses survived and exist today. Ammonites lay fragile eggs that are vulnerable to sudden changes in condition whereas nautiluses lay eggs that can handle rapid changes in outdoor conditions. Most of the current species that exist today derive from species that survived previous mass extinction. Ironically, species that survive one mass extinction cannot survive all mass extinctions. In the case of the Ammonites, the small eggs allowed the ocean waters to distribute the species all over the globe to survive a mass extinction. However, the rapid climate changes in the Cretaceous mass extinction proved too much for the fragile ammonite eggs to bear and therefore became extinct. As Landman told the author in page 91, “their hatchlings would have been like plankton, which for all of their existence would have been terrific. What better way to get around and distribute the species?” [(R) Landman wrapped up the demise of the ammonites perfectly. Throughout their existence, their small eggs proved to be major advantages for resilience to catastrophes since their species would be distributed across the globe. However, when a certain event like the asteroid affects the whole planet, the small eggs became huge disadvantages that led to their demise due to global cooling. This connects to the theme that Earth is an interconnected system since biogeochemical systems vary in ability to recover from disasters.]