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Unformatted text preview: rre Burgess Shale creatures = new phyla h l Phyla tend to have distinct body plans Thus, more *morphological disparity in Cambrian than any other High *morphological disparity = things look really different from each other Contingency
An event that may occur; a possibility Current events are contingent (~dependent) upon past events Changes in the past have lasting repercussions in the future Mass extinctions give opportunities for new groups to become dominant
But perhaps even more important... The Cambrian may have been an particularly important time for a specific body plan to survive and/or become dominant 23 2/19/2008 Addendum: Snowball Earth The evidence
(Note: some slides repeated from lecture material for clarity) The Snowball Earth idea Joe Kirschvink (Cal Tech) in 1992 introduces term "Snowball Earth" Paleomagnetic analyses on glacial deposits indicated glaciers at the equator Postulated glaciers covered the entire Earth including tropics He had no good explanation for initiation and demise of Snowball Earth 24 2/19/2008 The Snowball Earth Hypothesis Paul Hoffman (Harvard) in 1998 proposed a `unified' Snowball Earth hypothesis Earth experienced vary high temperature oscillations in the Neoproterozoic, from very cold ("snowball Earth") to very hot Neoproterozoic ( snowball Earth ) Let's look at the geological evidence... Neoproterozoic glacial deposits
Neoproterozoic g p glacial deposits occur on all modern continen...
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- Spring '08