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Copy of Plate Tectonics
Transcript of Copy of Plate Tectonics
areas where plates move toward each other and collide
area where two plates slide against each other
Where an oceanic and continental plates collide, the oceanic plate plunges beneath the less dense continental plate. As the plate descends, molten rock forms and rises toward the surface, forming volcanoes
areas where two plates move away from each other
As a result of pressure, friction, and plate material melting in the mantle, earthquakes and volcanoes are common near convergent boundaries. When two plates move towards one another, they form either a subduction zone or a continental collision.
Along these boundaries, lava spews from long fissures and geysers spurt superheated water. Frequent earthquakes strike along the rift. Beneath the rift, magma—molten rock—rises from the mantle. It oozes up into the gap and hardens into solid rock, forming new crust on the torn edges of the plates. Magma from the mantle solidifies into basalt, a dark, dense rock that underlies the ocean floor. Thus at divergent boundaries, oceanic
crust, made of basalt, is created.
Alfred Wegener, German meteorologist
In 1912, Wegener hypothesized that all of the continents were at one time connected as one large landmass which he called
. Furthermore, his hypothesis stated that about 200 million years ago it broke apart and began slowly moving to their current positions. His hypothesis is referred to as "
In the 1960's, scientists developed a new theory that expanded Wegener's idea of continental drift. According to the theory of
, Earth's crust and part of the upper mantle are broken into sections. These sections, called plates, move on a plasticlike layer of the mantle.
are made of the crust and a part of the upper mantle. These two parts combined are the
. The plasticlike layer below the lithosphere is called the
. The rigid plates of the lithosphere float and move around on the asthenosphere.
Seafloor spreading helps explain continental drift in the theory of plate tectonics. When oceanic plates diverge, tensional stress causes fractures to occur in the lithosphere. Basaltic magma rises up the fractures and cools on the ocean floor to form new sea floor. Older rocks will be found further away from the spreading zone while younger rocks will be found nearer to the spreading zone.
When the two plates slide against each other at a transform boundary, the plates can slide in opposite directions or in the same direction at different speeds. When one plate slips past another suddenly, earthquakes occur.
are vertical (or nearly vertical) fractures where the blocks have mostly moved horizontally
The Kuril Islands are part of a volcanic island chain produced by the subduction of the Pacific Plate beneath the North American Plate (yes, the N.A. Plate).
When continental plates pull apart, they can form rift valleys. The African continent is separating now along the East African Rift Valley.
Where two continental plates collide, they push up the crust to form mountain ranges
Continents collide as India plows into Asia. The Indian Plain suddenly rises to the peaks of the Himalaya Mountain Range.
Layers of Earth
Earth is made up of three main layers: core, mantle and crust. The innermost layer is the
, which is solid and dense, made of mostly iron. The next layer, working towards the surface, is the outer core. The
is mainly liquid iron and is extremely hot. As the Earth rotates, the liquid outer core spins, creating the Earth's magnetic field. The next layer is the
a dense, hot layer of semi-solid rock approximately 2,900 km thick. The mantle, which contains more iron, magnesium, and calcium than the crust, is hotter and denser because temperature and pressure inside the Earth increase with depth. A portion of the upper mantle, called the
, consist of weak rock that can flow slowly. The outermost layer is the
, which is rigid and very thin. The
is part of the upper mantle and the crust.
In 1960, Hess made his single most important contribution, which is regarded as part of the major advance in geologic science of the 20th century. He suggested that the Earth's crust moved laterally away from long, volcanically active oceanic ridges.
, as the process was later named, helped establish Alfred Wegener's earlier concept of continental drift as scientifically respectable. This triggered a revolution in the earth sciences. Hess's report was formally published in his "History of Ocean Basins," which for a time was the single most referenced work in solid-earth geophysics.
An underwater mountain system that consists of various mountain ranges, typically having a rift valley running down the center
Seafloor spreading is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity