Plate tectonics

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Plate tectonics

Plate Tectonics

I, Alfred Wegner, was a scientist that made the hypothesis that all of the continents started as one super continent, Pangaea.

Nobody believed my theory, but we found fossils of species like Glossopteris and Mesosarus on completley different continents, which was unlikley because these plants and animals could not cross the ocean, which meant at some time, these lands were once connected. Glaciation was also found. Glaciation is finding remains of glaciers on warm climate land. For exapme samples of ice was found in South Africa and India, which means they were once in a cold area and drifted.

My original theory was that the continents drifted apart because they simply plowed through the ocean. But other scientists needed proof. They came to the conclusion that the Earths' mantle, and the crust, are moving. They move because of intense heat beneath the surface, and this heat causes the two to slide apart, making the crust (continents) drift.

*There are different plate boundries, divergent and convergent. divergent are when two plates are shifting away from each other. And then there are convergent boundaries which are commonaly known in three different forms. Subduction is when the lighter plate rubs on top of the denser plate below it.

*When you have an ocean to oceanic plate boundary, island arcs can be found. An island arc is a chain of volcanoes underwater that erupt above the surface to make islands.

*Around an oceanic to continental plate boundary, a volcanic arc can form. A volcanic arc is volcanoes on top of tectonic plates, that when they erupt, the lava doesn't go above the surface, it flows out and instantly cools from the cold water.

Continent to Continent

Continent to Ocean

Oceanic to Oceanic

*On continent to continent boundries subduction can't happen becasue the plates are aroud the same density, so the plates fold and push up the land creating mountains.

Transform Plate Boundary is a strike slip, two plates rubbing together parallel to each other moving in opposite direction, fault but it is deeper than the lithosphere.

Sea floor spreading helps explain continental drift. When oceanic plates diverge stress causes a fracture to the earth's lithosphere. Harry Hess was a geologist and a navy submarine comander during the time of World War 2. His missions included to study the deep parts of the opcean floor. In 1946 he discovered hundreds of mountains, possibly islands had sunken, had made the pacific ocean floor. In 1960 he had made a proposition that the continents moving was a result of sea floor spreading. Vine and Matthews: Geophysicist Fredrick John Vine and geologist Drummon Matthews realized that if the seafloor spreading theory made by Harry Hess was true, then the rocks that had surrounded the mid oceanic ridges would show symemetric patterns of magnatism. Paleomagnetism is the measure of magnetic fields. The imaginary movement of the earth's magnetic poles relative to a continent that is not moving. The magnetic reversals are when the earth's magnetic field flips.Throughout history the magnetic field has flipped from normal to reverse and back to normal. In the past 5 million years, the magnetic field has flipped about 30 times. Basaltic basaltic magma is created by the melting of the earth’s mantle and doesn’t have as much silica as andesitic or rhyolitite magma. Andesitic magma is created by earth’s crust when it melts and has more silica than basalitic magma.Plate tectonics tell us that the earth’s rigid outer shell is broken into a mosaic of oceanic and continental plates which can slide over the asthenosphere.Mantle convection is a slow motion of the earth’s mantle caused by convection currents carrying heat from the interior of the earth to the surfaceHot spots are volcanic region where rocks melt to generate magma. For example the Yellowstone hot spot has been active for 15 years. When a hot spot lies beneath a continental plate, hot spots generate enormous volumes of layers and layers of lava.

Faults: When rocks break due to force. Folds when rocks bend due to force. Also there are areas around the earth where compression/ stress from plates cause fractures called faults and the North American plate lies east of the fault. And because both plates push together, it causes a fault. By the way the state of California is moving it will be up near Alaska in the next million years.Earthquakes: An earthquake is when the surface of the Earth is shaking because of rapid movement of the rocky outer layer of the earth. A focus is where the point of the earthquake originates from. Shallow earthquakes show us that earthquakes are formed if the focus of a quake is near the surface of the earth (0-40 miles deep). A deep focus point is when the deep point is within the earth (40-100 miles deep).A rift valley forms from earth’s crust that spreads/splits apart. (picture)Oceanic trenches: deepest part of the ocean. Trenches are formed from plate tectonics that slip underneath each other also known as subduction.

Harry Hess

By: Emily Krabbe and Sophia Morin



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