Frank Valoy- Chapter 4: The Luck of the Ammonites

         In chapter 4, Elizabeth Kolbert begins to talk about Walter Alvarez, who found traces of asteroid dust in a thin layer of clay in a gorge at Gubbio. Based on the sequence of the Gubbio limestone, it contradicted Lyell and Darwin’s belief that the disappearance of a species is a gradual process. It was soon discovered that a tremendous amount of iridium was found in these clay samples, indicating that an asteroid once hit Earth and the iridium-filled debris from the hit spreaded all around. (P) When I was reading this part in the chapter, I predicted that the asteroid hitting Earth related to the extinction of the dinosaurs.

  When looking back at the fossil records, it was noticed that large intervals of time was lost. Many became skeptical because this would mean that there was a sudden and drastic change. Supporting evidence of the hypothesis about the asteroid was found such as the presence of shocked quartz in the clay layer. This was considered evidence because shocked quartz is formed by high pressure.

Later on in the chapter, ammonites were introduced. They look like spiral shells with chambers. The animal inside the shell is found in the last and largest chamber. Since the bodies of the ammonites can’t be preserved, many inferences are made about its life and appearance.

Adding on to the hypothesis of the asteroid hitting the Earth, it was believed that the dust (bolide) traveled 45,000 mph at an angle from the Southeast in the Yucatán Peninsula to North America. As a result, many species died out, which explains why there wasn’t a large interval of time in the fossil record because of this catastrophic event. Many land animals died out such as the dinosaurs, birds, and snakes. Many marine species died out like the ammonites.

A quote that I found interesting in this chapter stated, “But mass extinctions were not to be confused with ‘catastrophes’”( Pg. 79). (Q) Would it be safe to say that catastrophes can cause mass extinctions?

  I feel that this chapter overall connects to the theme “Science is a process” because when there wasn’t a large interval of time present in the fossil record, it seemed unusual at first. However, the hypothesis about the asteroid hitting Earth allowed for a better understanding of this sudden change in the fossil record.