112lect30 - GY 112 Lecture Notes D Haywick(2006 1 GY 112...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
GY 112 Lecture Notes D. Haywick (2006) 1 GY 112 Lecture Notes Mesozoic Overview Lecture Goals : A) The end of the Paleozoic B) Mesozoic time frame and evolutionary developments C) Paleogeography and key tectonic events Textbook reference: Levin 7 th edition (2003) Chapters 11 & 12; Levin 8 th edition (2006) Chapters 13 & 14 A) The end of the Paleozoic A few lectures ago, I hinted that the Paleozoic came in with a bang (the Cambrian explosion) and went out pretty much the same way. With a bang. The terminal Paleozoic event was the greatest mass extinction recorded in geology 1 . Depending on who you talk to (or whose articles you read), 90 to 98% of the living plants and animals bit the big one (i.e., went extinct). Marine animals were the worst hit. Trilobites (a sub-phylum) entirely went extinct during the Permian (but possibly before the major extinction event). Rugose corals also died off. The mass extinction opened up all sorts of new niches for new animal and plant species to occupy in the Mesozoic. We will discuss these new evolutionary developments a bit later in this lecture. So what caused the extinction? There are a group of scientists who believe that it had to have been extraterrestrial . They claim that the sudden demise of so many species is very similar to what occurred at the end of the Mesozoic which is now generally accepted as a impact-generated extinction event. However, it needs to be clearly stated that no Paleozoic-ending impact site has been located on the planet. If it impacted in the ocean (a likely event given that the Earth is 70% water covered), no record of this impact will ever be found. Ocean crust is a maximum of 200 million years old due to recycling at plate boundaries. Interesting carbon molecules (fullerenes) have been found in some Permian-Triassic sedimentary rocks that may support an impact, but the jury is still out on this one. Others have suggested that a nearby star went supernova (a star blowing up within a few light years of our solar system would bath the Earth in enough radiation to extinguish much of our life). The problem with these hypotheses is that there is no way to test them, at least not yet. That doesn’t mean that they are incorrect, just that they can’t be evaluated. In science, like life in general, we find the exotic more interesting than the mundane. It is more appealing to think that some huge asteroid hit us or that a star exploded as a method of causing a mass extinction then a 1 You always have to remember that the Phanerozoic is the shortest Eon and has the most complete fossil record. The terminal Paleozoic event saw the demise of more marine and terrestrial species then any after it, but this may not be the same as saying it was the worst extinction ever. It is quite possible that “worse” extinctions occurred in the Proterozoic, but little was preserved to record them.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
GY 112 Lecture Notes D. Haywick (2006) 2 more traditional explanation like climate change. The biggest mass extinction occurred
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

Page1 / 7

112lect30 - GY 112 Lecture Notes D Haywick(2006 1 GY 112...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online