TPO 39At the end of the Triassic period 200 million years ago there was a mass extinction event that caused the extinction of more than half of all living species It was this extinction event that allowed dinosaurs to become the dominant species for the

Contrary to the three theories presented by the reading passage, the lecture explains why none of these three were practical.

Firstly, the passage mentions that the extinction might be caused by the decline of sea levels, as it could destroy the lives living in the shallows and on the coast, hence breaking the whole food chain. However, the lecture argues that though the sea levels were indeed downed, the period of this change, which is about several million years, was long enough for these lives to adapt to the environmental change gradually.

Secondly, the passage points out that climate cooling caused by the sulfur dioxide released by the volcanoes could also be the reason. Again, the lecture disagrees as the sulfur dioxide can only stay in the atmosphere for decades, as it will combine with water and become rainfall back to the ground. A few decades are relatively a short time for such extinction to happen.

Lastly, the passage asserts that asteroid strikes that throw up large amounts of debris contenting soil and rock, shadowing the sky and blocking out sunlight for months, could have caused this extinction, too. Opposing this idea, the lecture notes that although some scientists believe in this theory, there are no sites of crater found to support this. The only crater discovered can be dated back to twelve million years before the extinction, which is relatively impossible to be the actual cause.