* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Plate Tectonics Chapter Challenge sample
Survey
Document related concepts
Geomagnetic reversal wikipedia , lookup
Spherical Earth wikipedia , lookup
Ocean acidification wikipedia , lookup
Geochemistry wikipedia , lookup
History of geomagnetism wikipedia , lookup
Age of the Earth wikipedia , lookup
Oceanic trench wikipedia , lookup
Physical oceanography wikipedia , lookup
History of Earth wikipedia , lookup
Abyssal plain wikipedia , lookup
History of geology wikipedia , lookup
Mantle plume wikipedia , lookup
Geological history of Earth wikipedia , lookup
Transcript
Floating…on the Plates of the World By: Rachel Aldrich The Interior Structure of the Earth The Earth is made up of four main layers: ► Crust ► Mantle ► Outer core ► Inner core The Crust Continental crust forms Earth’s continents, and is generally 30-50 km thick. Some continental crust is as old as four billion years. Oceanic crust is found under the Earth’s oceans, and is only 5-10 km thick. All oceanic crust is younger than 200 million years old. The Mantle The mantle is located under Earth’s crust. The upper layer of the mantle, which moves like a rigid block that carries the crust with it, is called the lithosphere. The asthenosphere is below the lithosphere. It acts like a stiff liquid on which the less dense plates of the lithosphere “float.” Earth’s plates are composed of the lithosphere! Evidence for Movement Fossil Evidence Fossils of the freshwater reptile Mesosaurus were found in South American and Africa Remains of Glossopteris, a tropical fern, have been found in Australia, India, Antarctica, South America and Africa How could these organisms be found in so many different places that are separated by oceans today? Puzzle Fit Earth’s continents fit together like the pieces of a puzzle. They must have been joined together at some time in the past! Climate Clues Fossils of tropical plants were found on the island of Spitsbergen in the Arctic Ocean. All of these places must have had tropical climates in the past and were located close to the equator. Glacial evidence has been discovered in Africa, South America, India and Australia. Rock Evidence Parts of the Appalachian Mountains of the eastern U.S. are similar to mountains found in Greenland and western Europe. Rock structures found in eastern South America are similar to those found in western Africa. These areas must have been connected in the past! More Evidence for Movement Magnetic striping on GPS satellites the ocean floors monitor the shows that the movement of seafloor spreads apart Earth’s at mid-ocean ridges. lithospheric Magnetite rocks obtain plates. the polarity of Earth’s magnetic field as new ocean crust forms. The stripes are a record of past magnetic pole reversals, or paleomagnetism. Scientists drilling into the ocean floor found that the age of rock becomes increasingly older further from the center of the ridge. Plate Boundaries There are three types of plate boundaries: 1. 2. 3. Divergent Convergent Transform Divergent Plate Boundaries These are places where Earth’s lithospheric plates are moving away from each other. Mid-ocean ridges are found in all of the ocean basins. As the plates spread apart a crack, or rift forms. Magma rises up to fill the crack, creating mid-ocean ridges. An example is the MidAtlantic Ridge, a 10,000-mile long stretch of underwater volcanoes that runs through the Atlantic Ocean. Convergent Plate Boundaries Recall that there are two types of crust: •Continental These are places where Earth’s plates a moving toward each other. •Ocean Therefore, there are three types of convergent boundaries: •ocean/ocean •ocean/continental •continental/continental When two oceanic plates converge, one plate stays at the surface, and the other dives down beneath it at some angle in a process called subduction. Ocean trenches and island arc volcanoes are formed at ocean/ocean convergent boundaries. When an ocean plates collides with a continental plate, the denser ocean plate slides under the lessdense continental plate. Island arc volcanoes and ocean trenches form at the edge of the continental plate. As an oceanic plate travels from a mid-ocean ridge to a subduction zone, hundreds of meters of sediment is scraped off the ocean floor and added to the edge of the continental plate. The growth of a continent along its edge in this way is called continental accretion. When two continental plates collide, no subduction takes place because the lithosphere is much less dense than the mantle. Instead, the plates collide and crumple up, forming mountain ranges. The zone where two continents have met and become welded into a single continent is called a suture zone. An example of this can be found where the Indian Plate collided with the Eurasian Plate, creating the Himalayas. Transform Plate Boundaries These are places where plates slide past each other. The San Andreas Fault is a transform plate boundary that forms between the North American Plate and the Pacific Plate. How Do the Plates Move? Wegener and other scientists had discovered evidence to support the idea of moving plates and the existence of Pangaea. However, they could not explain HOW or WHY the plates moved. Flow of Matter and Energy within the Earth The temperature of the Earth increases with depth. Sources of Earth’s heat include: •The original heat of Earth’s formation •Impacts by meteorites early in Earth’s history •Decay of radioactive elements Temperature affects the density of materials. As rocks in Earth’s mantle are heated enough, their density increases. The less dense rock rises to the surface slowly over time. When plates of the lithosphere diverge, lava oozes out of the cracks, creating new seafloor. As the lithospheric plates continue to diverge over time, the new seafloor moves further away from the ridge and cools. As it cools, it becomes more dense and sinks back into the mantle, where it is heated and rises again. This pattern of heating and rising, cooling and sinking in Earth’s mantle is known as thermal convection. Many scientists today believe that these convection cells in the mantle are the driving force for the movement of lithospheric plates.