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Ch. 1 Dynamic and Evolving Earth ESCI 518 Fall 2004 Earth is a Dynamic and Evolving Planet • changes in its surface • changes in life Historical Geology • in historical geology we study – changes in our planet – how and why past events happened – implication for today’s global ecosystems • 3 main ideas of historical geology – plate tectonics – evolution – uniformitarianism Plate Tectonic Theory • Lithosphere is broken into individual pieces called plates • Plates move over the asthenosphere – as a result of underlying convection cells Theory of Organic Evolution • provides a framework for understanding the history of life • Darwin’s On the Origin of Species by Means of Natural Selection, published in 1859 • revolutionized biology Central Thesis of Evolution • all present-day organisms – are related – descended from organisms that lived during the past • Natural Selection is the mechanism that accounts for evolution – results in the survival to reproductive age of those organisms best adapted to their environment History of Life • Fossils are the remains or traces of onceliving organisms – demonstrate that Earth has a history of life – most compelling evidence in favor of evolution Geologic Time • human perspective – seconds, hours, days, years • ancient human history – hundreds or even thousands of years • geologic history – millions, hundreds of millions, billions of years Geologic Time Scale • resulted from the work of many 19th century geologists who – pieced together information from numerous rock exposures – constructed a sequential chronology based on changes in Earth’s biota through time • the time scale was subsequently dated in years – using radiometric dating techniques Geologic Column and the Relative Geologic Time Scale Absolute ages (the numbers) were added much later. Geologic Time Scale Uniformitarianism • Uniformitarianism is a cornerstone of geology – present-day processes have operated throughout time – physical and chemical laws of nature have remained the same through time • to interpret geologic events – we must first understand present-day processes and their results How Does the Study of Historical Geology Benefit Us? • survival of the human species depends on understanding how Earth’s various subsystems work and interact – how we consume natural resources and interact with the environment determines our ability to pass on this standard of living to the next generation – our standard of living depends directly on our consumption of natural resources that formed millions and billions of years ago • study what has happened in the past, on a global scale, to try and determine how our actions might affect the balance of subsystems in the future Latest Precambrian / Early Paleozoic Supercontinent Rodinia, centered about the south pole, breaks apart. North America (Laurentia), Baltica, and Siberia moved North. Marine Invertebrates. North America: arc on the south. Baltica and Siberia moved in from the SE. Texas (505-570 Ma): Flat plain; remnants of eroded collisional belt (Llano). Shallow marine seas across much of Texas. Sandy sediment onshore, limestone offshore. Trilobites, brachiopods. http://vishnu.glg.nau.edu/rcb/globaltext.html Latest Precambrian / Early Paleozoic Supercontinent Rodinia continues to break apart. Pieces move north. -Fish. -Glaciation. North America: Numerous plates and continental blocks move in from the south and east. The Taconic arc collides, forming the Taconic orogeny. Texas 438-505 Ma: Shallow marine seas across much of inland Texas. Warm-water limestone. Corals, brachiopods. http://vishnu.glg.nau.edu/rcb/globaltext.html Middle / Late Paleozoic Remains of Rodinia (Gondwana) move northward to collide with Laurasia -- creating the super continent Pangaea and the Tethys Ocean. First land-plants. Baltica collides with North America in the Caledonian-Acadian orogeny. Texas 403-438 Ma: Shallow marine seas across much of west Texas limestone. Corals, brachiopods. http://vishnu.glg.nau.edu/rcb/globaltext.html Middle / Late Paleozoic Most drifting Rodinia blocks assembled into the super continent of Laurussia. Amphibians. Fish really get going. Ferns. Glaciation. North America: Caledonian-Acadian orogeny marks assemblage of Laurussia. Gondwana closed in from the south. An arc formed along western North America. Texas 360-408 Ma: shallow marine sandstones and limestones in west Texas. http://vishnu.glg.nau.edu/rcb/globaltext.html Middle / Late Paleozoic Gondwana, with a large, developing glacier, nears southern Laurussia. Fern-forests. North America: The Antler arc collides with western North America creating the Antler orogeny. Texas 320-360 Ma: shallow marine seas inland. Shales and limestones. http://vishnu.glg.nau.edu/rcb/globaltext.html Middle / Late Paleozoic Rodinia blocks of Laurussia and Siberia collide to form Laurasia. Reptiles. North America: Gondwana collides from the south. The resulting Appalachian, Ouachita, Marathon, Ural, Variscan, and Hercynian orogenies formed some of the largest mountains of all time. The Ancestral Rockies form. Texas 286-320 Ma: Ouachita Mountains. Collision formed inland basins filled by seas. Limestone, sandstone, shale. http://vishnu.glg.nau.edu/rcb/globaltext.html Latest Paleozoic / Early Mesozoic The supercontinent Pangeae dominates the Permian Earth, lying across the equator. Extinctions! Trilobites go away. North America: A new arc approaches western North America. A new spreading center forms as Cimmeria rifts from Gondwana and opens the Tethyian Ocean. The western fringe of Pangaea lay along the eastern margin of the Pacific "ring of fire” subduction zone. Texas 245-286 Ma: Shallow marine inland of mountains. Reefs. Evaporites. Red shales. http://vishnu.glg.nau.edu/rcb/globaltext.html Latest Paleozoic / Early Mesozoic Mammals. North America: Arc collision along western edge forms the Sonoman orogeny. As the Tethys Ocean expands, Cimmeria (Turkey, Iran, and Afghanistan) move northward towards Laurasia. Texas 208-245 Ma: shales and sandstones in NW. Start opening the GOM - red sandstone, shale, evaporites. http://vishnu.glg.nau.edu/rcb/globaltext.html Middle Mesozoic Pangaea rotates; different components at different rates / in different directions -- rifts form. Birds. North America: Southern North Atlantic Ocean opens, continuing west into the Gulf of Mexico. The Cordilleran arc develops along Pacific margin. Arc forms on western side. Nevadan orogeny begins. Cimmeria begins collision with Laurasia - Cimmerian orogeny. Texas 144-208 Ma: Change in sediment direction. Shallow water deposition / evaporites in GOM. http://vishnu.glg.nau.edu/rcb/globaltext.html Middle Mesozoic The Atlantic continues to expand as Pangaea breaks up. The Cimmerian orogeny continues. North America: Arcs and micro continents slam into western region. Laramide orogeny in Rockies. Texas 66-144 Ma: Influx of sediment from Rockies. Shallow Cretaceous sea way across Texas. Shallow liestones, shales. http://vishnu.glg.nau.edu/rcb/globaltext.html Late Cretaceous / Present Rifts separate Africa and South America and then India, Australia, Antarctica. North America rifts from Europe. Old Gondwana lands(Africa, India, Australia) move north toward Eurasia, closing the Tethys Ocean and forming the Alpine-Himalayan mountains. The Atlantic lengthens / widens, the Sevier orogeny continues, and the Caribbean arc forms. Texas 65-144 Ma: continuing shallow limestone and shale deposition to the southeast (from Rockies). http://vishnu.glg.nau.edu/rcb/globaltext.html Paleocene / Eocene Himalayan Orogeny. Alps and Pyrenees form. The modern patterns of Planet Earth appear. Atlantic continues to open. Rocky Mountains grow. Texas 65 - 35 Ma: shale and sandstone in southeast region prograde shoreline (from the Rockies). Volcanic activity in Panhandle. http://vishnu.glg.nau.edu/rcb/globaltext.html Oligocene and Miocene Orogeny continues in the Mediterranean region and India nears its junction with southern Asia. Antarctica isolated. Southwestern North America intercepts the East Pacific Rise and a great extensional event, the Basin and Range orogeny begins. Texas 35-5 Ma: continued sandstone/shale deposition and progradation of shoreline (erosion of Rockies) http://vishnu.glg.nau.edu/rcb/globaltext.html Present Note: Best data set available. http://vishnu.glg.nau.edu/rcb/globaltext.html Fossils • Fossils are the remains or traces of prehistoric organisms – Any evidence of past life • Most common in sedimentary rocks – and in some accumulations of pyroclastic materials, especially ash • They are extremely useful for determining relative ages of strata – geologists also use them to ascertain environments of deposition • Fossils provide some of the evidence for organic evolution – many fossils are of organisms now extinct How do Fossils Form? • Remains of organisms are called body fossils – mostly durable skeletal elements such as bones, teeth and shells – rarely we might find entire animals preserved by freezing or mummification Trace Fossils • Indications of organic activity including tracks, trails, burrows, and nests are called trace fossils • A coprolite is a type of trace fossil consisting of fossilized feces that may provide information about the size and diet of the animal that produced it Trace Fossils • A land-dwelling beaver, Paleocastor, made this spiral burrow in Nebraska Trace Fossils • Fossilized feces (coprolite) of a carnivorous mammal – specimen measures about 5 cm long and contains small fragments of bones Body Fossil Formation • The most favorable conditions for preservation of body fossils occurs when the organism – possesses a durable skeleton of some kind – and lives in an area where burial is likely • Body fossils may be preserved as – unaltered remains, meaning they retain their original composition and structure,by freezing, mummification, in amber, in tar – altered remains, with some change in composition or structure by being permineralized, recrystallized, replaced, carbonized Unaltered Remains • Insects in amber • Preservation in tar Unaltered Remains • 40,000-yearold frozen baby mammoth found in Siberia in 1971 – hair around the feet is still visible Altered Remains • Petrified tree stump in Florissant Fossil Beds National Monument, Colorado Altered Remains Carbon film of a palm frond Carbon film of an insect Fossil Record • The fossil record is the record of ancient life preserved as fossils in rocks • The fossil record is very incomplete because of: – – – – bacterial decay physical processes scavenging metamorphism • In spite of this, fossils are quite common