Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Geomagnetic reversal wikipedia , lookup
Paleontology wikipedia , lookup
Physical oceanography wikipedia , lookup
Geochemistry wikipedia , lookup
Biogeography wikipedia , lookup
Abyssal plain wikipedia , lookup
Oceanic trench wikipedia , lookup
History of geology wikipedia , lookup
Large igneous province wikipedia , lookup
Geological history of Earth wikipedia , lookup
CONTINENTAL DRIFT http://www.tectonics.caltech.edu/movi es/outreach/sumatra/pangaea.mov The Story of Alfred L. Wegener There once was a German Geologist who noticed similar rocks & fossil remains were found on continents which seemed to fit together He called this “super” continent called Pangaea In 1912 Wegener published the first version & died defending his theory PANGAEA the large landmass that included all of Earth’s present day continents WEGENERS CONTINENTAL DRIFT Alfred Wegener in the early 1900’s proposed the hypothesis that continents were once joined together in a single large land mass he called Pangaea (meaning “all land” in Greek). WEGENERS CONTINENTAL DRIFT He proposed that Pangaea had split apart and the continents had moved gradually to their present positions - a process that became known as continental drift. Pangaea about 200 million years ago, before it began breaking up. Wegener named the southern portion of Pangaea Gondwana, and the northern portion Laurasia. The continents about 70 million years ago. Notice that the breakup of Pangea formed the Atlantic Ocean. India’s eventual collision with Eurasia would form the Himalayan Mountains. The position of the continents today. The continents are still slowly moving, at about the speed your fingernails grow. Satellite measurements have confirmed that every year the Atlantic Ocean gets a few inches wider! Support for Continental Drift 1. SHAPE OF THE CONTINENTS Continents fit together like puzzle pieces Support for Continental Drift 1. SHAPE OF THE CONTINENTS Wegener was not the only one to notice the fit of the continents. 1858: Antonio Pelligrini depicted Africa and South America connected. He was one of the first scientists to publish maps depicting the apparent fit of the continents. Support for Continental Drift 2. FOSSIL EVIDENCE SAME FOSSILS: DIFFERENT CONTINENTS Mesosaurus was incapable of swimming across a large ocean. Evidence for Continental Drift Lystrosaurus: mammal like reptile, herbivore, about the size of a small dog. Mesosaurus: freshwater reptile, carnivore. Glossopteris: extinct seed fern was about 12 ft (3.6 m) tall. Cynognathus: metrelong predator of the Lower Triassic. It was one of the more mammal-like of the "mammal-like reptiles", Support for Continental Drift 3. ROCK EVIDENCE – Mountain ranges SAME ROCK: DIFFERENT RANGE Existing mountain ranges separated by vast oceans contain rocks of identical mineral content. A prime example are the Appalachian Mountains in the eastern U.S and the Caledonian Mountains in the British Isles. Support for Continental Drift 3. ROCK EVIDENCE – Mountain ranges Rock sequences (meaning he looked at the order of rock layers) in South America, Africa, India, Antarctica, and Australia show remarkable similarities. Wegener showed that the same three layers occur at each of these places. Picture from http://volcano.und.edu/vwdocs/vwlessons/plate_tectonics/p art4.html Support for Continental Drift 4. GLACIAL SCARS/ CLIMATE CHANGE SAME SCARS: DIFFERENT CONTINENTS • The land area that shows evidence of this glaciation now lies near the equator in a subtropical or tropical climate. Support for Continental Drift 5. LOCATION OF COAL tropical DEPOSITS/ CLIMATE • Large swamps existed CHANGE during the same time in the Northern Hemisphere with lush vegetation which eventually became the coal fields of the eastern U.S., Europe, and Siberia. Support for Continental Drift 5. LOCATION OF COAL DEPOSITS/ CLIMATE CHANGE Coal deposits have been found in temperate and polar regions; however, coal is formed in tropical regions. CONTINENTAL DRIFT IN DOUBT Why didn’t people believe in continental drift? People couldn’t image how the earth could be millions of years old People couldn’t image a force great enough to move the continents Wind and currents could possibly move fossils Theory was not accepted by scientists CONTINENTAL DRIFT IN DOUBT Everyone agreed that Wegener’s evidence was compelling. But wouldn’t we feel the movement? Also, wouldn’t there be evidence to show that the continents were still moving today? Wegener was a meteorologist and his theory was not well accepted. (He died on an expedition in Greenland collecting ice samples) BUT by the 1960’s evidence would prove continental drift is TRUE and…. The story continues (as does all good science!) Seafloor Spreading One reason scientists had a hard time with Wegener’s theory is that there was no mechanism for the continents motion. Then comes along seafloor spreading! Seafloor Spreading Picture from USGS http://pubs.usgs.gov/gip/dynamic/HHH.html In the 1960’s, a scientist named Henry Hess made a discovery that would vindicate Wegner. Using new technology, radar, he discovered that the seafloor has both trenches and mid-ocean ridges. Henry Hess proposed the sea-floor spreading theory. Seafloor Spreading Hess proposed that hot, less dense material below Earth’s crust rises toward the surface at the midocean ridges. Then, it flows sideways, carrying the seafloor away from the ridge in both directions. Picture from http://library.thinkquest.org/17457/platetectonics/4.php Seafloor Spreading As the seafloor spreads apart at a mid-ocean ridge, new seafloor is created. The older seafloor moves away from the ridge in opposite directions. This helped explain how the crust could move—something that the continental drift hypothesis could not do. Evidence for Spreading In 1968, scientists aboard the research ship Glomar Challenger began gathering information about the rocks on the seafloor. Scientists found that the youngest rocks are located at the mid-ocean ridges. Mechanism for Plate Tectonics Seafloor Spreading provided insight to the mechanism for how the continents moved. The magma which pushes up at the midocean ridge provides the new land pushing the plates, and the subduction zones The mechanism that gobble up the land on made continental drift the other side of the was convection plates. currents! Picture from http://library.thinkquest.org/17457/platetectonics/2.php Plate Tectonic Theory Both Hess’s discovery and Wegner’s continental drift theory combined into what scientists now call the Plate Tectonic Theory. Theory of plate tectonics: • The Earth’s crust and part of the upper mantle are broken into sections, called plates which move on a plastic-like layer of the mantle Tectonic plates move. The boundaries created where they meet are called FAULTS Three types of plate boundary Divergent Convergent Transform There are three types of plate movement boundaries 1. Divergent Also known as seafloor spreading Plates are separating from each other as a new land mass forms This is seen at midocean ridges and rifts Plate separation is a slow process. For example, divergence along the Mid Atlantic ridge causes the Atlantic Ocean to widen at only about 2 centimeters per year. Picture from www.geology.com Author Hobart M. King Rift Valleys are areas where the crust is pulling away slowly. There are three types of plate movement boundaries 2. Convergent Two continental plates collide. & crumple the edges of the plates & form mountains. We can see the end result of the collision between the Indian & Eurasian plates which are the Himalayan Mountains. Picture from USGS Picture from www.geology.com Author Hobart M. King Continent-Oceanic Crust Collision SUBDUCTION is another type of a convergent plate movement. Subduction Oceanic crust and lithosphere subducts underneath the continental crust and lithosphere Oceanic lithosphere heats and dehydrates as it subsides The melt rises forming volcanism E.g. The Andes Ocean-Ocean Plate Collision When two oceanic plates collide, one runs over the other which causes it to sink into the mantle forming a subduction zone. The subducting plate is bent downward to form a very deep depression in the ocean floor called a trench. The worlds deepest parts of the ocean are found along trenches. E.g. The Mariana Trench is 11 km deep! There are three types of plate movement boundaries 3. Transform Two plates slide past each other Example: San Andreas Fault in California Picture from www.geology.com Author Hobart M. King Divergent Convergent Transform Plate Tectonic Theory Plate Tectonics explains Earthquakes Mountains Volcanoes