Plate Tectonics
What Makes Up The Structure Of The Earth?
-the earth is made up of 3 main layers: -core, inner and outer -mantle -crust Crust -Continental crust- is thick, buoyant (less dense than oceanic crust) and oldest -Oceanic crust- is tin, dense (sinks under continental crust) and young. What Is Continental Drift? -Alfred Wegener in the early 1900s proposed that the continents were once joined together in a single large land mass he called Pangea. -He proposed that Pangea had split apart and the continents had moved gradually to their presents positions- a process that became known as continental drift. What Are Wegeners Evidences? #1-Continents fit together like a puzzle. the coastlines to Africa and south america -the best fit includes the continental shelves. #2-Fossils of planets and animals of the same species found on different continents. #3- Rock sequences in south america, Africa, India, Antarctica, and Australia show remarkable similarities. -Wegener showed that the same three layers occur at each of these places. What Is Seafloor Spreading? -in the 1960s a scientist named Henry Hess made a discovery that would vindicate wegener. -using new technology, radar, he discovered that the seafloor has both trenches and mid ocean ridges. -Henry Hess proposed the seafloor spreading theory. -Hess proposed that hot, less dense material below Earths crust rises toward the surface at the mid ocean ridges. -then it flows sideways carrying the seafloor away from the ridge in both directions. |
Plate tectonics- earths crust and part of the upper mantle are broken into sections called plates which move on a plastic like layer of the mantle.
-Plates of lithosphere are moved around by the underlying hot mantle convection cells. What Happens At Tectonic Plate Boundaries? -1 Divergent- spreading ridges as plates move apart new material is erupted to fill the gap. Iceland is an example of continental rifting and has a divergent plate boundary running through its middle. -2 Convergent- 3 styles of theses plate boundaries, continent-continent collision they form mountains, continent-oceanic crust collision also called subduction is where one goes underneath the other one and volcanoes are made. Oceanic-oceanic collision, one runs over the other which causes it to sink into the mantle forming a subduction zone, and forms a trench. -3 Transform- Where plates slide past each other. |
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Geological Time Scale
How Are Fossils Useful To Us?
-Ancient fossil and rock data provide relative dates of past events. -The rock record has contributed to our modern day geologic time scale, a record of Earth’s history from 4.6 bya to the present. How Do We Divide Geological Time? -Eons= largest division (billions of years) -Era= hundreds of millions of years; based on fossilized life forms found in rocks. -Cenozoic (recent life) -Mesozoic (middle life) -Paleozoic (ancient life) -Periods= tens of millions of years; based on life forms that were abundant OR became extinct. -Epochs= smallest division (millions of years) -ONLY in the Cenozoic Era because rocks and fossils are more easily accessed (not buried or destroyed). Why Does Earths Surface Change? -Principle of Uniformitarianism -The processes occurring on Earth today have been occurring since it formed, BUT the rate and intensity have changed. -Ex: erosion, earthquakes, sea levels. Why Are Rocks Stripped? -Principle of Original Horizontality -Sedimentary rocks are deposited in nearly horizontal layers. |
How Do We Know Relative Age?
-Principle of Superposition -Oldest rocks are on the bottom, each successive layer is younger. -Principle of Faunal Succession -Oldest fossils are in the bottom layers, successive layers are younger. -Principle of Cross-Cutting Relationships -An intrusion is younger than a rock it cuts across. What About Gaps In The Rock Record? -Unconformities -Layers get shifted up or down -Layers get eroded Why Does It Matter? -Correlation= matching rock regions in one area to another area. -Helps determine sequence of events in Earth’s history. |