Were the continents always located in the same position? http://www.wwnorton.com/co llege/geo/egeo/flash/2_1.swf http://www.classzone.co m/books/earth_science/t erc/content/visualizatio ns/es0806/es0806page0 1.cfm?chapter_no=08 Drift animations
In 1912 a German meteorologist named Alfred Wegener noticed that the continents fit together like puzzle pieces. He proposed that the continents were joined together in the past, in a large land mass called Pangaea. http://www.sci.csuhayward.edu/~lstrayer/geol2101/2101_Ch19_03.pdf
Over time, the continents drifted apart – Wegener named his theory “Continental Drift”.
He supported his theory with four pieces of evidence. 1. Puzzle like fit of continent edges http://maps.google.com
2. Matching fossils of plants and animals on once connected land areas. Fossils of Glossopteris are found in Permian rocks of South Africa, India, Australia, South America, and Antarctica
3. Rock similarities and ages Mountains in South America and Antarctica are believed to have formed as part of the same mountain chain.
4. Climate evidence (Glacial evidence in Africa, South America, Australia, and India and tropical plant fossils in Arctic areas) Fossils found in Antarctic soil indicate that the now frigid continent was once lush with trees and ferns, and home to dinosaurs, amphibians, and later, marsupials.
Wegener’s theory made sense, but no one wanted to accept it until they knew HOW the continents moved.
In the 1960’s, a Princeton University scientist named Harry Hess, discovered how the continents drifted. Continental Drift Whiplash
Seafloor Spreading Magma in the mantel rises and pushes the plates apart, forming new oceanic crust. http://education.sdsc.edu/optiputer/flash/seafloorspread.htm
Supporting evidence of seafloor spreading 1. Magnetic iron particles record the time of the rock formation. http://www.wwnorton.com/college/geo/egeo/flash/2_3.swf http://www.wwnorton.com/college/geo/egeo/flash/2_3.swf 2. Rocks farther away from the opening age at the same rate on both sides. http://www.wwnorton.com/college/geo/egeo/flash/2_5.swf http://www.wwnorton.com/college/geo/egeo/flash/2_5.swf
A map of the ocean floor provides even more evidence http://maps.google.com/ http://maps.google.com/
Iceland shows seafloor spreading above the water, which makes it easier to study
Plate Tectonic Theory Theory of Plate Tectonics -Earth’s crust is broken into plates which float and move.
Earth’s crust made of many plates is similar to the panels on the outside of a soccer ball.
There are about 13 plates covering Earth’s surface
Plate Boundaries (edges) When the plates move, their boundaries, or edges, can scrape and collide. http://www.wwnorton.com/college/geo/egeo/flash/2_6.swf
Convergent Boundary Plates move toward each other
Convergent Boundary When two continental plates move into each other, the plates combine and form mountains. (India into Asia) http://www.classzone.com/books/earth_science/terc/content/visualizations/es1105/es1105page01.cfm?chapter_no=visualization
Convergent Boundary When an oceanic plate runs into a continental plate, the heavier oceanic plate subducts (sinks) back into the mantle. Volcanic mountains are created along this edge.
Oceanic plate into continental Example: Pacific plate (oceanic) subducts (sinks) under Japan (continental). http://maps.google.com/ http://maps.google.com/
When both diverging plates are both oceanic, it is called seafloor spreading (Mid-Atlantic Ridge)
When both diverging plates are continental it is called rift valley formation (Africa) http://highered.mcgraw- hill.com/olcweb/cgi/pluginpop.cgi?it=swf::640::480::/sites/dl/free/0072402466/30425/19_21.swf::Fig.%2019.21% 20-%20Evolution%20of%20a%20Divergent%20Plate%20Boundary
Transform Boundary Plates slide past each other
Asthenosphere A plastic-like layer found below the lithosphere. The rigid oceanic and continental plates of the lithosphere sit on top
The Asthenosphere is heated by the hot Outer Core
Convection Current Hot material rises, cooler material sinks, creating a current, called a Convection Current core mantle crust
When the asthenosphere moves, it carries the lithospheric plates (divergent, convergent, and transform motions) Convection currents cause plate motion http://www.absorblearning.com/media/attachment.action?quick=12p&att=2775
Every time these plates move we get earthquakes, volcanic eruptions, and possibly tsunamis