112lect25 - GY 112 Lecture Notes D. Haywick (2006) 1 GY 112...

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GY 112 Lecture Notes D. Haywick (2006) 1 GY 112 Lecture Notes Cambrian Explosion Lecture Goals : A) Phanerozoic time frame (Paleozoic Era) B) Why a Cambrian “explosion” C) Introducing our ancestors Textbook reference: Levin 7 th edition (2003), Chaptes 10; Levin 8 th edition (2006), Chapter 12 A) The Time Frame Welcome to the Phanerozoic . This eon is the most critical one as far as life is concerned for several reasons. There is an abundant fossil record in the Phanerozoic, one that allows geologists to piece together a pretty good evolutionary story. The diverse fossils also provide geologists with very fine time resolution. We can resolve events on a sub-million year basis (compare this with our resolution of Archean or Proterozoic events – we were lucky to date events to the nearest +/- 10 million years!). The other thing to note about the Phanerozoic is that it is the last of the 4 geological eons. That makes it special because you are living in it. Because of the importance of the Phanerozoic, we are going to spend a lot of time (the rest of the course!) looking at it. To make life even easier, we divide the Phanerozoic into 3 eras . The first of these, the Paleozoic (245 to 550 MA), is the subject for the lecture today (and several others to follow). Today, we will simply set the scene for the more detailed lectures to follow. The Paleozoic lasted 300 million years, which, compared to the span of the Proterozoic, was a comparatively brief period; however, a lot happened over that time. It started with a evolutionary bang ( Cambrian explosion ) and ended with the largest extinction event ever ( Permian-Triassic Extinction event ). We saw the arrival of fish and other marine animals, terrestrial plants, amphibians, reptiles Era Cenozoic (0 to 65 MA) Mesozoic (65 to 245 MA) Phanerozoic Paleozoic (245 to 550 MA) Note: This lecture will provide you with a brief overview or summary of the material that we will be covering over the next several weeks in the lectures and the labs. The Paleozoic was a pivotal time in the Earth’s history and a LOT of stuff went on over the 300 million years it spanned. A tremendous amount of data has now been collected about the fossils and tectonic history of the Paleozoic. We can only touch on the basics in this class. If you are interested in learning more, see me and I’ll point you to some excellent books and papers that are available in South’s library.
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GY 112 Lecture Notes D. Haywick (2006) 2 and insects. In short, the ancestors of everything showed up. There were several major extinctions besides the Permian-Triassic event (see arrows on the diagram to left from http://exobio.ucsd.edu). The subdivisions of the Paleozoic (geological periods ) reflect the evolution and demise of fossil life on the planet. As a matter of fact, most of the geological periods have informal age designations based upon fossil content. The Silurian and the Devonian are known as the Age of the Fishes . Non-USA based geologists refer
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112lect25 - GY 112 Lecture Notes D. Haywick (2006) 1 GY 112...

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