The Earth's Plates Virginia SOL 5.7d K. Benzie Cave Spring Elem.
The Earth's Plates Plate tectonics is the theory that the Earth's crust is broken up into 12 major plates. These plates are slowly drifting on top of the mantle. The plates move both horizontally and vertically. Over billions of years, the location and size of the plates has changed. This movement has caused the formation of mid-ocean ridges, ocean basins, ocean trenches, and mountain ranges. This movement is believed to be caused by the Earth's internal heat.
The Earth's Plates Every continent is thought to be embedded with these plates. If the plates are moving, the continents are moving, too! The idea that the continents are changing their positions is called the continental drift theory. Some plates appear to be drifting almost one inch each year, carrying the continents with them.
The Earth's Plates In 1915, German geologist Alfred Wegener proposed his theory of continental drift. He also proposed that at one time (about 200 million years ago) there had been one supercontinent. He named this supercontinent Pangaea. Pangaea contained all of the Earth's landmasses until it began to break up. The continuous movement of the Earth's plates has since resulted in the locations of the continents as we know them today.
The Earth's Plates To support his theory of continental drift and Pangaea, Wegener offered fossil evidence. He found identical animal fossils on different continents. He found plant fossils on continents where the plants could no longer grow. However, it was only when it was discovered that the sea floor is spreading that Wegener's theory gained the scientific backing that it needed.
The Earth's Plates The movement of the plates affects the surface of the Earth. Mountains, volcanoes, and deep ocean trenches are all a result of the plates coming together. The are three different types of plate boundaries: A. Divergent plates B. Convergent plates C. Transform boundaries
The Earth's Plates Divergent boundaries are found where the plates are moving away from each other. As the plates pull apart, magma rises up from the mantle and forms new rock. Most divergent boundaries are found along the crests of mid ocean ridges. This "pulling apart" leads to underwater volcanoes and sea floor spreading. As plates pull apart on land, valleys dotted with volcanoes develop.
The Earth's Plates Convergent plates are pushing against each other. When plates collide, energy is released and new landforms are produced. Mountains rise and/or volcanoes erupt. Often when plates collide, one plate slips under the other. This is called a subduction zone. The part of the plate that slipped under the other may melt into magma which pushes upward. If enough magma reaches the surface, a volcano erupts.
The Earth's Plates The are three types of convergent plates. Ocean - Ocean Convergence The denser, older plate will sink (subduct) under the younger, lighter plate. Volcanic islands are created at these convergent boundaries. The Philippine Islands are an example. Ocean - Continent Convergence Oceanic plates always subduct. Mountains, like the Andes, are formed at these boundaries. Continent - Continent Convergence Neither plate subducts. Land crumples into mountains. The Himalayas are an example.
The Earth's Plates The final type of boundary is a transform boundary. A transform boundary, or transform fault, occurs where plates slide along each other. Faults are breaks in the Earth's crust that form plate boundaries. When plates scrape and slide past each other, they shake the Earth's surface. As plates grind past each other, they sometimes slip, causing earthquakes. The San Andreas fault is a famous transform boundary.
LLet's review! • wPPPPlate tectonics says that the Earth's crust is broken into 12 • major plates. • wAAccording to the continental drift theory, these plates are • sslowly moving. At one time, all the continents were joined in • oo one supercontinent named Pangaea. • wCConvergent boundaries are where plates collide with each • other. Mountains and volcanoes result from convergent • bbboundaries. • wDDivergent boundaries are where plates pull apart from each • oother. This is what causes sea floor spreading. • wTTransform boundaries are where plates slide past each • oother. TThis is where earthquakes happen. The Earth's Plates