German meteorologist Alfred Wegener is often credited as the first to develop a theory of plate tectonics, in the form of continental drift.
Scientists discovered later that Pangea fragmented early in the Jurassic Period. The heat source is thought to be the decay of radioactive elements. How this convection propels the plates is poorly understood. Some geologists argue that upwelling magma at spreading centres pushes the plates, whereas others argue that the weight of a portion of a subducting plate one that is forced beneath another may pull the rest of the plate along.
The Ring of Fire is a long horseshoe-shaped earthquake-prone belt of volcanoes and tectonic plate boundaries that fringes the Pacific Ocean basin. For much of its 40,km 24,mile length, the belt follows chains of island arcs such as Tonga and Vanuatuthe Indonesian archipelagothe PhilippinesJapanthe Kuril Islandsand the Aleutiansas well as other arc-shaped features, such as the western coast of North America and the Andes Mountains.
The skin has been broken into many different plates because of differences in the density of the rock and differences in subsurface heating between one region and the next. The concept of plate tectonics was formulated in the s. According to the theory, Earth has a rigid outer layer, known as the lithospherewhich is typically about km 60 miles thick and overlies a plastic moldable, partially molten layer called the asthenosphere.
The lithosphere is broken up into seven very large continental- and ocean-sized plates, six or seven medium-sized regional plates, and several small ones. These plates move relative to each other, typically at rates of 5 to 10 cm 2 to 4 inches per year, and interact along their boundaries, where they converge, diverge, or slip past one another. Plate motions cause mountains to rise where plates push together, or converge, and continents to fracture and oceans to form where plates pull apart, or diverge.
The theory of plate tectonics is based on a broad synthesis of geologic and geophysical data. It is now almost universally accepted, and its adoption represents a true scientific revolution, analogous in its consequences to quantum mechanics in physics or the discovery of the genetic code in biology.
What Is the Theory of Plate Tectonics?
For details on the specific effects of plate tectonics, see the articles earthquake and volcano. A detailed treatment of the various land and submarine relief features associated with plate motion is provided in the articles tectonic landform and ocean.
In essence, plate-tectonic theory is elegantly simple.
While the interiors of the plates are presumed to remain essentially undeformed, plate boundaries are the sites of many of the principal processes that shape the terrestrial surface, including earthquakes, volcanismand orogeny that is, formation of mountain ranges. For a deeper discussion of plate-driving mechanisms, see Plate-driving mechanisms and the role of the mantle. Plate tectonics.Shiratorizawa x manager reader
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Submit Feedback. Thank you for your feedback. Plate tectonics geology. Written By: Tjeerd H.Plate tectonics is a theory that was first proposed in the early s by scientist Alfred Wegener, but was not said to be true until the s. When Alfred Wegener first proposed the theory of continental drift, he described the tectonic plates, or the continents, as puzzle pieces fitting together. He continued to explain his theory after realizing the Earth's surface changing significantly over time while noticing that continents which, at one point, were not separated, were.
This was also noted by paleontologists when fossils of the same species were found on different continents, now separated. Their combined observations determined that the Earth's lithosphere had, in fact, been moving over time.
Was this helpful? Yes No I need help 1 Controversy. Not everyone agreed with Wegener's theory, as there wasn't really a way to prove why the continents were moving, other than his observation.
Many other scientists believed it was due to the Earth's temperatures, causing continents to contract. Was this step helpful? Yes No I need help 2 Disproved.Train simulator 2019 joystick
Wegener originally proposed that Earth's continents pushed against the ocean floors, although he was unable to identify the direct cause of continental drift. For that reason, geologists deemed his theory false; however, it did lay the groundwork for the development of plate tectonics and over time, additional evidence was gathered.
Yes No I need help 3 Seismometers. After World War II, several seismometers were installed all over the world, in order to monitor nuclear testing. This is what ultimately lead to the discovery of tectonic plates.
Their findings showed that earthquakes and volcanoes formed along the edges of tectonic plates. Yes No I need help 4 s. In the s is when the plate tectonic theory started to gain acceptance across the world. Yes No I need help The Plates The tectonic plates are found in the Earth's lithosphere, which is the outermost shell, or in other words, the crust and the mantle combined. The lithosphere is broken up into seven or eight major tectonic plates, as well as several minor ones.Steve J.
Baedke home e-mail: Baedkesj jmu. Lynn S. Fichter home e-mail: Fichtels jmu. The drawing above is a cross section of the earth showing the components that lie within plate tectonic theory. The cross section should really be curved to correspond to the earth's curvature, but it has been straightened out here.
Note the continental craton stable continent in the middle of the drawing. Note the line under the craton; that is the lower boundary of the plate.Kris kross overalls
Everything above that line is the plate. All similar lines in the cross section mark the bottom of the plates. Technically, everything above that line is lithosphere, the rigid, brittle shell of the earth.
Everything below is asthenospherethe hot, plastic interior of the earth. Within the asthenosphere are convection cellsslowly turning over hot, plastic rock. The convection cells bring heat from the earth's interior out to the surface, but slowly.
Movement is about 10 centimeters a year. When the convection cells reach the base of the lithosphere they release heat to the surface at the divergent plate boundary to escape to space. The cooled plastic rock then turns sideways and moves parallel to the earth's surface before descending back into the earth at subduction zones to become reheated.
It is this turning over of the convection cells the drives the plate movements. Observe that 7 different plates are labeled in the cross section. Plates are combinations of two units, continents and ocean basins. It is possible a plate could be a continent alone, but for this to occur all edges of the continent would have to be a plate boundary very rare, perhaps not practically possible.From the deepest ocean trench to the tallest mountain, plate tectonics explains the features and movement of Earth's surface in the present and the past.
Plate tectonics is the theory that Earth's outer shell is divided into several plates that glide over the mantle, the rocky inner layer above the core. The plates act like a hard and rigid shell compared to Earth's mantle. This strong outer layer is called the lithosphere, which is km 60 miles thick, according to Encyclopedia Britannica.
The lithosphere includes the crust and outer part of the mantle. Below the lithosphere is the asthenosphere, which is malleable or partially malleable, allowing the lithosphere to move around. How it moves around is an evolving idea. Developed from the s through the s, plate tectonics is the modern version of continental drifta theory first proposed by scientist Alfred Wegener in Wegener didn't have an explanation for how continents could move around the planet, but researchers do now.
There are nine major plates, according to World Atlas. These plates are named after the landforms found on them. The largest plate is the Pacific Plate at 39, square milessquare kilometers. Most of it is located under the ocean. It is moving northwest at a speed of around 2.
The driving force behind plate tectonics is convection in the mantle. Hot material near the Earth's core rises, and colder mantle rock sinks. The convection drive plates tectonics through a combination of pushing and spreading apart at mid-ocean ridges and pulling and sinking downward at subduction zones, researchers think.
Scientists continue to study and debate the mechanisms that move the plates. Mid-ocean ridges are gaps between tectonic plates that mantle the Earth like seams on a baseball. Hot magma wells up at the ridges, forming new ocean crust and shoving the plates apart. At subduction zonestwo tectonic plates meet and one slides beneath the other back into the mantle, the layer underneath the crust.
The cold, sinking plate pulls the crust behind it downward. Many spectacular volcanoes are found along subduction zones, such as the "Ring of Fire" that surrounds the Pacific Ocean. Subduction zones, or convergent margins, are one of the three types of plate boundaries. The others are divergent and transform margins. At a divergent margin, two plates are spreading apart, as at seafloor-spreading ridges or continental rift zones such as the East Africa Rift.
Transform margins mark slip-sliding plates, such as California's San Andreas Faultwhere the North America and Pacific plates grind past each other with a mostly horizontal motion. While the Earth is 4.Dhara 12 kya hai
The oldest ocean rocks are found in the northwestern Pacific Ocean and the eastern Mediterranean Sea. Fragments of continental crust are much older, with large chunks at least 3. With clues left behind in rocks and fossils, geoscientists can reconstruct the past history of Earth's continents.
Most researchers think modern plate tectonics began about 3 billion years agobased on ancient magmas and minerals preserved in rocks from that period. Some believe it could have started a billion years after Earth's birth, at around 3. As the continents jostle around the Earth, they occasionally come together to form giant supercontinentsa single landmass. One of the earliest big supercontinents, called Rodinia, assembled about 1 billion years ago.
Its breakup is linked to a global glaciation called Snowball Earth. A more recent supercontinent called Pangaea formed about million years ago. Africa, South America, North America and Europe nestled closely together, leaving a characteristic pattern of fossils and rocks for geologists to decipher once Pangaea broke apart.
The puzzle pieces left behind by Pangaea, from fossils to the matching shorelines along the Atlantic Ocean, provided the first hints that the Earth's continents move. Plates bumping into each other can also cause mountain ranges.Plate tectonics is the scientific theory that attempts to explain the movements of the Earth's lithosphere that have formed the landscape features we see across the globe today.
By definition, the word "plate" in geologic terms means a large slab of solid rock. The theory of plate tectonics itself says that the Earth's lithosphere is made up individual plates that are broken down into over a dozen large and small pieces of solid rock.plate tectonics
These fragmented plates ride next to each other on top of the Earth's more fluid lower mantle to create different types of plate boundaries that have shaped the Earth's landscape over millions of years. Plate tectonics grew out of a theory that was first developed in the early 20th century by the meteorologist Alfred Wegener. InWegener noticed that the coastlines of the east coast of South America and the west coast of Africa seemed to fit together like a jigsaw puzzle.
Further examination of the globe revealed that all of the Earth's continents fit together somehow and Wegener proposed an idea that all of the continents had at one time been connected in a single supercontinent called Pangaea. He believed that the continents gradually began to drift apart around million years ago - this was his theory that became known as continental drift.
The main problem with Wegener's initial theory was that he was unsure of how the continents moved apart from one another. Throughout his research to find a mechanism for continental drift, Wegener came across fossil evidence that gave support to his initial theory of Pangaea. In addition, he came up with ideas as to how continental drift worked in the building of the world's mountain ranges. Wegener claimed that the leading edges of the Earth's continents collided with each other as they moved causing the land to bunch up and form mountain ranges.
He used India moving into the Asian continent to form the Himalayas as an example. Eventually, Wegener came up with an idea that cited the Earth's rotation and its centrifugal force toward the equator as the mechanism for continental drift.
He said that Pangaea started at the South Pole and the Earth's rotation eventually caused it to break up, sending the continents toward the equator. This idea was rejected by the scientific community and his theory of continental drift was dismissed as well. InArthur Holmes, a British geologist, introduced a theory of thermal convection to explain the movement of the Earth's continents.
He said that as a substance is heated its density decreases and it rises until it cools sufficiently to sink again.
According to Holmes it was this heating and cooling cycle of the Earth's mantle that caused the continents to move. This idea gained very little attention at the time. By the s, Holmes' idea began to gain more credibility as scientists increased their understanding of the ocean floor via mapping, discovered its mid-ocean ridges and learned more about its age.The theory of plate tectonics states that the Earth's surface, the upper mantle and crust, was once made up of enormous rock plates that broke into smaller pieces approximately million years ago.
These smaller, broken plates form a more fluid rock surface in the mantle. Over time, the plates move and morph into natural land boundaries. This explains natural land phenomena, such as earthquakes and tsunamis. Inmeteorologist Alfred Wegener proposed the first plate tectonics theory: all of the continents, at one time, were connected and formed a single super-continent called Pangaea.
This explains why the coastlines of the continents appear to fit together like pieces of a puzzle. During hundreds of millions of years, the plates have moved and changed position.
Learn About the History and Principles of Plate Tectonics
Sometimes they move together, sometimes they separate and move apart and sometimes they move past each other. When the plates move past each other, they sometimes touch and make one plate rise up as the other slides down.
That up-down movement causes an earthquake, which results in a land fault or crack. If the movement happens in a large body of water, it can create giant water waves called tsunamis. Home Science. What Drives Plate Tectonics? Why Do Earthquakes Happen?The model builds on the concept of continental driftan idea developed during the first decades of the 20th century.
The geoscientific community accepted plate-tectonic theory after seafloor spreading was validated in the late s and early s. The lithosphere, which is the rigid outermost shell of a planet the crust and upper mantleis broken into tectonic plates.
The Earth's lithosphere is composed of seven or eight major plates depending on how they are defined and many minor plates. Where the plates meet, their relative motion determines the type of boundary: convergentdivergentor transform.
Earthquakesvolcanic activitymountain -building, and oceanic trench formation occur along these plate boundaries or faults. Tectonic plates are composed of oceanic lithosphere and thicker continental lithosphere, each topped by its own kind of crust.
Along convergent boundaries, subductionor one plate moving under another, carries the lower one down into the mantle ; the material lost is roughly balanced by the formation of new oceanic crust along divergent margins by seafloor spreading.
In this way, the total surface of the lithosphere remains the same. This prediction of plate tectonics is also referred to as the conveyor belt principle.
What Is the Theory of Plate Tectonics?
Earlier theories, since disproven, proposed gradual shrinking contraction or gradual expansion of the globe. Tectonic plates are able to move because the Earth's lithosphere has greater mechanical strength than the underlying asthenosphere.
Lateral density variations in the mantle result in convection ; that is, the slow creeping motion of Earth's solid mantle. Plate movement is thought to be driven by a combination of the motion of the seafloor away from spreading ridges due to variations in topography the ridge is a topographic high and density changes in the crust density increases as newly formed crust cools and moves away from the ridge. At subduction zones the relatively cold, dense oceanic crust is "pulled" or sinks down into the mantle over the downward convecting limb of a mantle cell.
The relative importance of each of these factors and their relationship to each other is unclear, and still the subject of much debate. The outer layers of the Earth are divided into the lithosphere and asthenosphere. The division is based on differences in mechanical properties and in the method for the transfer of heat.
The lithosphere is cooler and more rigid, while the asthenosphere is hotter and flows more easily. In terms of heat transfer, the lithosphere loses heat by conductionwhereas the asthenosphere also transfers heat by convection and has a nearly adiabatic temperature gradient. This division should not be confused with the chemical subdivision of these same layers into the mantle comprising both the asthenosphere and the mantle portion of the lithosphere and the crust: a given piece of mantle may be part of the lithosphere or the asthenosphere at different times depending on its temperature and pressure.
The key principle of plate tectonics is that the lithosphere exists as separate and distinct tectonic plateswhich ride on the fluid-like visco-elastic solid asthenosphere. Tectonic lithosphere plates consist of lithospheric mantle overlain by one or two types of crustal material: oceanic crust in older texts called sima from silicon and magnesium and continental crust sial from silicon and aluminium.
Because it is formed at mid-ocean ridges and spreads outwards, its thickness is therefore a function of its distance from the mid-ocean ridge where it was formed. The location where two plates meet is called a plate boundary. Plate boundaries are commonly associated with geological events such as earthquakes and the creation of topographic features such as mountainsvolcanoesmid-ocean ridgesand oceanic trenches.
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