What is plate tectonics?
The Earth’s surface is covered by rigid, moving land masses called plates. Some plates, such as the North American Plate and the Eurasian Plate, are moving together. The study of the formation and movement of these plates is called Plate Tectonics. The Earth’s crust and mantle were thought to represent two different materials. now we have learned that they are both similar in rock composition and physical properties. Both make up a layer known as the lithosphere. The lithosphere is composed of igneous rock basalt. Continental crust is composed more of igneous rock granite. Granite is less dense than basalt and therefore continents only occur in the denser part of the lithosphere. The lithospheric plates are resting on a layer called the asthenosphere. The asthenosphere rock is partially melted, so the layer is able to flow. The flow makes up large slow moving convection currents. Within these currents, material will expand and rise while heating, but will contract and sink while coolin
Plate tectonics is the study of how the Earth’s plates are driven and shaped by geological forces that keep them in constant motion. It would appear as though the outermost crust of the Earth is one solid shell. In reality it is cracked into several large pieces or slabs called plates that average 50 miles thick (80 km). These plates float on a partially molten mantle beneath. The molten layer is believed to be in a constant state of convection driven by heat from the Earth’s inner core. Convection cells, which are circular in nature, act like conveyer belts that slowly move the plates floating above. Currently there are 14 main plates and many smaller subplates. The main plates are: • Pacific plate • Juan de Fuca plate • North American plate • South American plate • Caribbean plate • Cocos plate • Nazca plate • Scotia plate • Antarctica plate • African plate • Arabian plate • Eurasian plate • Indian-Australian plate • Philippine plate Continents and seabeds alike sit atop these slabs
According to the theory of plate tectonics, the earth’s crust is broken into a number of large irregularly shaped slabs of rock called “plates.” The plates move slowly on the surface of the earth, much like large icebergs in an arctic lake. There are two types of plates: continental and oceanic. They are composed of different materials. Continental plates consist of relatively lightweight minerals such as quartz and feldspar. An example of a continental plate is the North American plate. Oceanic plates consist of heavier and more dense minerals like basalt. An example of an oceanic plate is the Pacific plate. Alaska is situated in a unique and complex tectonic setting. At the southern edge of the state lies the boundary between the North American and Pacific plates. The Pacific plate is moving northwestward relative to, and being subducted under, the North American plate at an average rate of 5-7 centimeters per year. In southeastern Alaska, the plate boundary is defined by a series of
The theory of plate tectonics has revolutionized the thinking of geologists. This is a unifying theory that explains many seemingly unrelated geologic processes. Plate tectonics was first seriously proposed as a theory in the early 1960’s although the related idea of continental drift was proposed much earlier. The Plates The outer part of the earth is broken into rigid plates approximately 62 miles thick. These outer plates are called lithosphere and include rocks of the earth’s crust and upper mantle. Below the rigid lithosphere is the asthenosphere, a zone around the earth that is approximately 90 miles thick and behaves like a plastic because of high temperature and pressure. The lithosphere plates move over the plastic asthenosphere at a rate of an inch or more per year. Eight large plates and a few dozen smaller plates make up the outer shell of the earth. The internal heat of the earth is the most likely cause of plate movement; this heat is probably generated by the decay of ra
There are really only two processes: one that forms the physical earth, and another that beats up the surface and tears it apart through weathering and erosion. The formational process is called tectonics, and is manifested to those of us living on earth by earthquakes, volcanos, and mountain building in general. The earth is really just a sphere of liquid rock (magma) which has cooled to the solid state where exposed to the coldness of space. We call this cold and rigid outer shell the crust, and it is actually rather thin in comparison to the overall diameter of our planet. Because of the heat and pressure beneath the surface, this crust is constantly being subjected to stresses which break it up. The earth’s crustal sections are called plates, and they vary from small to continental in size. Immense forces cause these rigid plates to slowly move about the surface, where they are constantly running into each other. Tectonic activity is common at these plate boundaries, of which there
