Bio171-F11-Lec 28 - Biology 171 Friday Lecture 28 History...

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Unformatted text preview: Biology 171 Friday, November 11, 2011 Lecture 28: History of Life on Earth & Fossil Record Announcements Text Reading Lecture 28 : Chapter 27 (479-492) Lecture 29 : Chapter 28 (496-516) Age of the Earth Pre-Cambrian Life Concordance of Evidence Cambrian Explosion Post-Cambrian Diversification Mass-Extinction events Next week in Discussion: Frogs & Phylogeny Exam 3 – Wed. Nov. 16 8-10 PM. How Old Is the Earth? Meteorites formed 4.58 Gya (billions of years ago), and the Moon formed 4.51 Gya. Earth must be about the same age, but no direct radiometric dating is possible because Earth was initially molten. Events at plate boundaries. At some plate boundaries, such as oceanic ridges, the plates separate, and molten rock wells up in the gap. The rock solidifies and adds crust symmetrically to both plates, causing seafloor spreading. At subduction zones, where plates move toward each other, the more dense plate dives below the less dense one, forming a trench. Samples of the earth's oldest rocks are extremely rare because rock is constantly recycled or sinks to the hot mantle of the Earth. MYA Zircon crystals with ages >4000 Ma have been found in these rocks, including a 4,404 +/- 8 Myr zircon. The rocks themselves are younger (3800 Ma). The oldest dated material on Earth. Using the Fossil Record The fossil record is the only source of direct evidence about what prehistoric organisms looked like, where they lived, and when they existed. Paleontologists —scientists who study fossils—recognize that they are limited to asking questions about tiny and scattered segments on the tree of life. Yet analyzing fossils is the only way scientists have of examining the physical appearance of Using the Fossil Record The fossil record is the only source of direct evidence about what prehistoric organisms looked like, where they lived, and when they existed.lived, and when they existed....
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This note was uploaded on 11/22/2011 for the course BIO 171 taught by Professor Josephinekurdziel during the Fall '08 term at University of Michigan.

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Bio171-F11-Lec 28 - Biology 171 Friday Lecture 28 History...

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