After lunch, Dr. Donald Prothero of Occidental College talked about various catastrophes from the planet's past.

First up was the hypothesis that a comet or asteroid hitting the Earth killed off the dinosaurs and caused a mass extinction. Prothero surveyed the evidence for an ancient asteroid collision, but noted that the evidence that such an impact killed off the dinosaurs has problems. Among other things, marine reptiles and invertebrates began to die off before the potential impact, while other species were not effected at all by the alleged impact event. From the available evidence, it does not appear that an asteroid impact killed off the dinosaurs. Indeed, of the five mass extinctions in the Earth’s history, only one shows evidence of an impact event, and there is evidence for several substantial asteroid impacts that do not appear to have had any impact on extinction rates.

Prothero notes that scientists have sought to find a single cause for all five major extinction events in the Earth’s history. However, as with asteroid impacts, no single cause is consistent with the all of the evidence. Volcanism and climate change both played a role in prior mass extinctions, but neither is the cause of prior mass extinctions.

Another interesting part of Prothero’s talk was about the prevailing theory for what caused the creation of the Arctic Ice Cap: The closure of the Isthmus of Panama. This was important because it altered ocean circulation. It also led to the intermixing of species that previously had only lived in South America (which had been an island up until this point).

The Earth is currently in an interglacial period, Prothero noted, and anotherglacial period (“Ice Age”). Because prior interglacials have typically lasted less than 10,000 years, the next glacial period should come along relatively soon – were it not for global warming. The likely outcome, Prothero suggests, is either a new glacial or a “super interglacial” produced by anthropogenic global warming. In the latter scenario, the Earth would be as warm as when dinosaurs roamed the Earth and crocodiles lived at the Arctic Circle.

Prothero ended an otherwise interesting talk by suggesting that any “controversy” over global climate change is ginned up by conservative think tanks and corporate-funded scientists, and that there is little in the peer-reviewed literature casting doubt on the threat of climate change.