The Sixth Extinction: Chapter 4

     In Chapter 4, Kolbert introduces us to Walter Alvarez, who discovered that a huge asteroid had hit the Earth during the Cretaceous period, causing the mass extinction of dinosaurs. While studying plate tectonics in Italy, he found out that the clay contained huge amounts of iridium, indicating that it came from an asteroid. The Alvarez theory, stated that at the end of the Cretaceous period an iridium asteroid struck the Earth, causing mass extinction of the dinosaurs. Many scientists rejected the theory as they said that extinction is a slow, gradual process. However, scientists discovered layers of shocked quartz and sandstone from the same period. They then found a huge crater in Mexico from the end of the Cretaceous era. Walter then concluded that the dust of the asteroid was responsible for the mass extinction of the dinosaurs. Large creatures like the dinosaurs were the first to go, followed by sea creatures and mammals. The mass-extinction of the dinosaurs brings up the concept of “preservation potential”, a way of scientists measuring the likelihood that a species will go extinct based on its population. Kolbert then meets with Neil Landman, who shows Kolbert a fossil site where there is a layer of iridium, rock, and soil at the site, along with hundreds of ammonite fossils. Landman explains that the ammonites died out very quickly, but the nautiluses survived and still exist today because they lay large, robust eggs that can survive sudden changes in temperature or water pressure. Kolbert then concludes that every life form on the planet came from a species that survived the mass extinction, but today’s species aren’t extinction proof because they survived a “past extinction”.

     (C) The debate on the Alvarez theory reminds me of the debate in the previous chapter about catastrophism vs. uniformitarianism. On pages 78-79 it states, "... Lyell concluded that the unaccounted- for interval must have been a long one... he observed that the disappearance of the ammonites seemed to be 'wonderfully sudden'... he dismissed the ammonites and what they seemed to be saying." (R) Alvarezes’ theory of the dinosaurs’ extinction shows the differences between catastrophism and uniformitarianism. However it also proves both of the theories right. For many millions of years, ammonites, dinosaurs, and other animals had been a part in the slow, gradual process of natural selection. But the arrival of an asteroid changed the natural selection process, making it almost impossible to survive on the Earth. The theme that connected the most to this chapter was: energy conversions underlie all ecological processes. I thought of the asteroid as an energy form that changed everything on the Earth. As it said in the book, it caused mass extinction to species like the dinosaurs and ammonites, however it also caused changes in the surroundings, as the surviving species such as the nautiluses and many other species found it very hard to adapt to their "new" environment. Because of this natural selection and survival of the fittest will come to a play later on due to many species not wanting to be extinct.

By: Mousumi Dhar