Journal Entry 4(Chapter Four)-Ziomara Aguilar

The author talks about the very popular theory of what killed the dinosaurs, the asteroid theory.
In the 1970s, Walter Alvarez, a geologist had discovered traces of an asteroid, later it was decided that the asteroid had hit the Earth during the Cretaceous period resulting in the extinction of the dinosaurs.

Later in 1980, Walter and his father, Luis Alvarez co-wrote a paper together claiming that the asteroid, which was rich in Iridium,  had collided into earth's surface and killed them at the end of the Cretaceous time period. This asteroid theory is an example of a catastrophist, which is mentioned in the previous chapter. Many scientists did not agree or believe the asteroid theory, they concluded that extinction happened slowly and gradually rather than it happening in a sudden way, the uniformitarian theory. But the asteroid theory was a more plausible theory because it explained both how the dinosaurs went extinct and why there was so much Iridium om Earth.

Kolbert talks about ammonite fossils later in the chapter, she talks to Landman who explains that ammonites also died out along with the dinos when the asteroid struck the earth. And although the Ammonites went extinct, there are organisms today that are very similar to Ammonites.  This is possible due to natural selection, they were able to grow and adapt because the eggs from which they were born changed so that they were more durable.

The theme connected to this chapter is that the Earth is one interconnected system because although the majority of the dinosaurs went extinct, those that did manage to survive were able to adapt and become some of the living organisms we know today.