"The Sixth Extinction" Chapter 4- Matthew Batista

By studying limestone sequences in Gubbio, Walter Alvarez discovered that species seemed to become extinct abruptly, but dismissed it due to his uniformitarianism view. By clocking the sediment with iridium, a common element in meteorites, Luis Alvarez (Walter's father) discovered massive amounts of iridium. Kolbert states, “Iridium is extremely rare on the surface of the earth but much more common in meteorites”(75). The Alvarez began to theorize why this could be and they finally came to the conclusion that “an asteroid six miles wide collided with the earth”(75). This sudden change in the environment caused multiple well adapted species to be unable to survive. When I think of the idea of dinosaurs going extinct it’s hard to think that this idea was recently created. New Jurassic movies are coming out every year and we forget that everyday we are learning new things about our world. 

Connecting back to the previous chapter, the ideology of both Lyell and Darwin still dominated the way of thinking. This meant that when the Alvarezes came out with a idea that went against uniformitarianism they received a lot of backlash. However, as more evidence came out people “gradually did come to to change their minds”(82). Connecting to the theme “Environmental problems have a cultural and social context,” the idea of extinction kept changing over the years. For years, people believed that extinction happened gradually but again Cuvier’s ideology came back and it shows how there was societal background to how we now understand extinction, an environmental issue. 

Kolbert explains that the main cause of the Cretaceous extinction event was not the impact of the asteroid but it was the dust created by the impact. The debris from the impact incinerated anything in its path(86). One class of animals that were affected by effects of the asteroid's impact, are the ammonites. Kolbert explains that, even though ammonites were fit for their current environment, a single moment can completely change which traits are advantageous and which are lethal. In the case of the ammonites, one possibility of their extinction was that “the resulting hatchlings… had no means of locomotion; they just floated near the surface of the water…”(90). This means that that toxins at the ocean surface could have killed the hatchlings. Even though, this chapter talked about natural “catastrophes” it’s also important to bring it back to the idea of human caused extinctions. Just like animals we don’t know how a sudden change in our climate will affect us. As global warming continues, we have no idea if we can handle the change and just because we strive now it doesn’t mean it will continue.