Paleozoic

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Published on October 3, 2007

Author: Julie

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The Paleozoic (Book chapters 10-12):  The Paleozoic (Book chapters 10-12) 570 Ma - 245 Ma Includes Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian Started with simplest multi-celled life Ended with the biggest extinction in the fossil record Paleozoic Time and Environments:  Paleozoic Time and Environments The Paleozoic can be divided into two cycles, each very similar Early Paleozoic - Cambrian, Ordovician, Silurian Late Paleozoic - Devonian, Carboniferous, Permian Paleozoic Time and Environments (continued):  Paleozoic Time and Environments (continued) Both Early and Late Paleozoic began with marine transgressions - shallow seas invade continents Both ended with a cyclic regression - more land exposed, less shallow marine habitat QUESTION: What controls sea level? First, some definitions... Sea Level:  Sea Level There are two kinds of sea level change: Eustatic = Global sea level change - e.g. add/remove water or increase/reduce ocean basin size Isostatic = Local sea level change - e.g. raise or lower local landmass - post-glacial rebound in Alaska Eustatic Sea Level Change:  Eustatic Sea Level Change Add or remove water - e.g. ice meteorites, volcanic activity, Ice sheets - the more ice there is on land, the less water there is in the oceans. Temperature - the warmer the ocean is, the less dense the ocean water is, and the higher sea level will be Eustatic Sea Level Change:  Eustatic Sea Level Change Plate Tectonics - a big factor in the Paleozoic transgressions and regressions How does plate tectonics affect sea level? Oceanic crust is hot when formed Hot crust is less dense, so it rides up higher on the asthenosphere due to isostasy Crust cools at a fairly constant rate upon exposure to the ocean Eustatic Sea Level Change and Plate Tectonics:  Eustatic Sea Level Change and Plate Tectonics If the oceanic crust is spreading rapidly (e.g. East Pacific Rise), then the oceanic crust will be less dense, and the ocean bottom will be shallower. This forces water up onto land. If the oceanic crust is spreading slowly (e.g. Mid-Atlantic Ridge), then the oceanic crust will be more dense, and the ocean bottom will be deeper. This draws water back down into the ocean basin Eustatic Sea Level Change and Plate Tectonics:  Eustatic Sea Level Change and Plate Tectonics What if you have a single supercontinent (e.g. Rodinia, Pangea) rather than a bunch of smaller continents? Typically, more continents mean more ocean ridges, and a younger average age for oceanic crust. That means you have shallower ocean basins and higher sea level. Paleozoic Time and Environments (continued):  Paleozoic Time and Environments (continued) Paleozoic contained both steady, slow sedimentation and also orogeny - episodes of mountain building Much of the Appalachians were built during the Paleozoic through a series of orogenies Isostatic sea level change:  Isostatic sea level change Sometimes the land moves up or down, usually through isostasy Remember, isostasy is when a plate floats higher or lower due to changes in thickness, density, or mass Examples of isostatic change include areas of sediment accumulation offshore (land sinks) and areas where ice was recently removed (land rises) Paleozoic Plate Tectonics:  Paleozoic Plate Tectonics The Proterozoic ended just as an early supercontinent (Rodinia) was breaking apart Oceans proceeded to widen and become better established as the Early Paleozoic passed Plate Tectonics Movie - Here Major Tectonic Events of the Appalachian Region:  Major Tectonic Events of the Appalachian Region Grenville Orogeny - 1.1 billion years ago - occurred when North America collided with another continent (Laurasia). Formed mountains, but only their roots still exist. Iapetus Ocean - 650 million years ago - North America pulled apart from the rest of Laurasia, creating an earlier version of the Atlantic. Major Tectonic Events of the Appalachian Region:  Major Tectonic Events of the Appalachian Region Iapetus lasts for about 200 million years. As it is closing, a subduction zone and island arc form. Major Tectonic Events of the Appalachian Region:  Major Tectonic Events of the Appalachian Region Taconic Orogeny - 445-435 million years ago - Iapetus closes, and an off-shore volcanic island arc (related to subduction - like Japan today) slams into North America, creating more mountains. These mountains begin to erode, creating thick sediments (4000 feet thick in some places - Catskill delta) across the east coast. Major Tectonic Events of the Appalachian Region:  Major Tectonic Events of the Appalachian Region Acadian Orogeny - 375-355 million years ago -Iapetus begins closing for good, and a new mountain range is forced up east of the fast-eroding Taconic mountains. Major Tectonic Events of the Appalachian Region:  Major Tectonic Events of the Appalachian Region Acadian mountains continue to erode, producing tons of sediments across the east coast. Alleghenian Orogeny - 320-220 million years ago -Iapetus finally closes completely as the northwestern part of Africa rams into North America (forming part of Pangea). This creates our modern Appalachian mountains. Major Tectonic Events of the Appalachian Region:  Major Tectonic Events of the Appalachian Region After the orogenies - 220 million years ago to the present - Pangea breaks up, forming the new Atlantic. The rifting of Africa and North America produces pull-apart basins which fill with sediments from the new mountains. There is also basaltic volcanism as dikes come up through the fractures in the rifting crust. Latest Proterozoic Life:  Latest Proterozoic Life At the end of the Proterozoic (Precambrian) life was just shifting toward multicelled forms - remember Ediacaran fauna Here are some pictures... Vendian organisms:  Vendian organisms Dickinsonia - Ediacara Hills - from UCMP web site Worm (Annelida) or coral (Cnidaria)? Vendian organisms:  Vendian organisms Tribrachidium - Ediacara Hills - from UCMP web site Annelida? Echinodermata? Something completely weird? Vendian organisms:  Vendian organisms Kimberella - White Sea (Russia) - from UCMP web site Was thought to be jellyfish at first, now new structures and symmetry point to mollusc Vendian organisms:  Vendian organisms Arkarua - Ediacara Hills - from UCMP web site Echinodermata? Has the right symmetry Cambrian Life:  Cambrian Life Base of the Cambrian is easy to spot in most places - set at the place where you first get shelled fossils There were a few Precambrian shelled species, but the “Cambrian Explosion” produced many more All phyla with hard parts (except Bryozoa) began in Cambrian, and many without hard parts too. Cambrian organisms:  Cambrian organisms Trilobite - from UCMP web site Dominant animal of the Cambrian (and much of Paleozoic) Cambrian organisms:  Cambrian organisms Brachiopods - from UCMP web site Dominant animal of the Cambrian (and much of Paleozoic) Remember, these guys had stalks Burgess Shale:  Burgess Shale Rich fossil beds in British Columbia What’s good about organic-rich shale for fossils? Shale has small clay-sized grains, which means the area was low-energy - less destruction of dead organisms, even soft ones Organic rich means the area where the organisms landed was anoxic - reduces decay and breakdown of dead organisms Walcott Quarry Burgess life discovered 1909 Quarry began 1910:  Walcott Quarry Burgess life discovered 1909 Quarry began 1910 Photo by Andrew MacRae from University of Calgary Burgess Shale web page: http://www.geo.ucalgary.ca/~macrae/Burgess_Shale/ Burgess Shale:  Burgess Shale Walcott initially described the burgess species by fitting them in to existing phyla Not a stupid thing to do - that’s how taxonomy works However, it turns out that the Burgess organisms represented a number of forms not seen before or since Burgess Shale Animals:  Burgess Shale Animals Photo by Andrew MacRae from University of Calgary Burgess Shale web page: http://www.geo.ucalgary.ca/~macrae/Burgess_Shale/ Anomalocaris claw - organism was up to 60 cm long Burgess Shale Animals:  Burgess Shale Animals From National Museum of Natural History (Smithsonian) Anomalocaris - about 60 cm long Burgess Shale Animals:  Burgess Shale Animals Photo by Andrew MacRae from University of Calgary Burgess Shale web page: http://www.geo.ucalgary.ca/~macrae/Burgess_Shale/ Marella Burgess Shale Animals:  Burgess Shale Animals Photo by Andrew MacRae from University of Calgary Burgess Shale web page: http://www.geo.ucalgary.ca/~macrae/Burgess_Shale/ Ottoia - worm-like organism Burgess Shale Animals:  Burgess Shale Animals Rendering by necrosis: http://www.bekkoame.or.jp/~necrosis/html/pageframe.htm Paediumias clarki Burgess Shale Animals:  Burgess Shale Animals Rendering by necrosis: http://www.bekkoame.or.jp/~necrosis/html/pageframe.htm Marella Burgess Shale Animals:  Burgess Shale Animals From National Museum of Natural History (Smithsonian) Wiwaxia - from 0.3-5 cm long Burgess Shale Animals:  Burgess Shale Animals From National Museum of Natural History (Smithsonian) Amiskwia - about one inch long Burgess Shale Animals:  Burgess Shale Animals From National Museum of Natural History (Smithsonian) Opabinia - Had five eyes! About 3 inches long + 1 inch tube nose Burgess Shale Animals:  Burgess Shale Animals From National Museum of Natural History (Smithsonian) Hallucigenia - about 1 cm long - which end is the head? Burgess Shale Animals:  Burgess Shale Animals From National Museum of Natural History (Smithsonian) Hallucigenia - incorrect reconstruction It’s walking on its protective spines Burgess Shale Animals:  Burgess Shale Animals From National Museum of Natural History (Smithsonian) Hallucigenia - actual photograph - note that it shows only one set of legs Concepts from Burgess:  Concepts from Burgess Cambrian was a time when many new forms appeared, many soft-bodied and not well preserved, but only a few survived Sparked a debate between punctuated equilibrium (Punk Eek) and continuous evolution What is the role of contingency versus fitness? How do we define fitness? What is our concept of evolution?:  What is our concept of evolution? What is our concept of evolution?:  What is our concept of evolution? What is our concept of evolution?:  What is our concept of evolution? What is our concept of evolution?:  What is our concept of evolution? Rise and fall of great faunal groups :  Rise and fall of great faunal groups Families Slide47:  Wikipedia image Slide48:  Wikipedia image Periodicity Sepkoski and others discovered a 62 million-year periodicity to their extinction records (R and W are background estimates) :  Periodicity Sepkoski and others discovered a 62 million-year periodicity to their extinction records (R and W are background estimates) Rhode and Muller, 1994. Cycles in Fossil Diversity. Slide51:  Some were 6-8 feet long - yikes

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