Topic 2 Inside The Earth Flashcards
Wegener’s conclusion to Mountain ranges
“Mountain ranges with the same rock types, structures, and ages are now on opposite sides of the Atlantic Ocean. The Appalachians of the eastern United States and Canada, for example, are just like mountain ranges in eastern Greenland, Ireland, Great Britain, and Norway. Wegener concluded that they formed as a single mountain range that was separated as the continents drifted.
Ancient fossils of the same species of extinct plants and animals are found in rocks of the same age but are on continents that are now widely separated. Wegener proposed that the organisms had lived side by side, but that the lands had moved apart after they were dead and fossilized. He suggested that the organisms would not have been able to travel across the oceans.”
Excerpt From: “Unit 2 Inside the Earth.” v1.0. iBooks.
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Continental Drift
“Identical rocks, of the same type and age, are found on both sides of the Atlantic Ocean. Wegener said the rocks had formed side-by-side and that the land had since moved apart.”
Evidence of continental drift
“Grooves and rock deposits left by ancient glaciers are found today on different continents very close to the equator. This would indicate that the glaciers either formed in the middle of the ocean and/or covered most of the Earth. Today glaciers only form on land and nearer the poles. Wegener thought that the glaciers were centered over the southern land mass close to the South Pole and the continents moved to their present positions later on.
Coral reefs and coal-forming swamps are found in tropical and subtropical environments, but ancient coal seams and coral reefs are found in locations where it is much too cold today. Wegener suggested that these creatures were alive in warm climate zones and that the fossils and coal later had drifted to new locations on the continents.”
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Scientists reaction to Wegener’s theory
“Scientists argued that there was no way to explain how solid continents could plow through solid oceanic crust. Wegener’s idea was nearly forgotten until technological advances presented even more evidence that the continents moved and gave scientists the tools to develop a mechanism for Wegener’s drifting continents.”
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Oldest sea floor
“The oldest seafloor is near the edges of continents or deep sea trenches and is less than 180 million years old. Since the oldest ocean crust is so much younger than the oldest continental crust, scientists realized that seafloor was being destroyed in a relatively short time.”
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Sea Floor Spreading Hypothesis
“In this hypothesis, hot buoyant mantle rises up a mid-ocean ridge, causing the ridge to rise upward.
The hot magma at the ridge erupts as lava that forms new seafloor. When the lava cools, the magnetite crystals take on the current magnetic polarity. As more lava erupts, it pushes the seafloor horizontally away from ridge axis.
The magnetic stripes continue across the seafloor.
As oceanic crust forms and spreads, moving away from the ridge crest, it pushes the continent away from the ridge axis.
If the oceanic crust reaches a deep sea trench, it sinks into the trench and is lost into the mantle.
The oldest crust is coldest and lies deepest in the ocean because it is less buoyant than the hot new crust.”
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Plate Boundaries
“Plate boundaries are the edges where two plates meet. Most geologic activities, including volcanoes, earthquakes, and mountain building, take place at plate boundaries. How can two plates move relative to each other?
Convergent plate boundaries: the two plates move towards each other.
Divergent plate boundaries: the two plates move away from each other.
Transform plate boundaries: the two plates slip past each other.
The type of plate boundary and the type of crust found on each side of the boundary determines what sort of geologic activity will be found there.”
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Ocean continent
“Ocean-continent: When oceanic crust converges with continental crust, the denser oceanic plate plunges beneath the continental plate. This process, called subduction, occurs at the oceanic trenches. The entire region is known as a subduction zone. Subduction zones have a lot of intense earthquakes and volcanic eruptions. The subducting plate causes melting in the mantle. The magma rises and erupts, creating volcanoes. These coastal volcanic mountains are found in a line above the subducting plate. The volcanoes are known as a continental arc.”
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Ocean-ocean
“Ocean-ocean: When two oceanic plates converge, the older, denser plate will subduct into the mantle. An ocean trench marks the location where the plate is pushed down into the mantle. The line of volcanoes that grows on the upper oceanic plate is an island arc.”
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Continent-continent
“Continent-continent: Continental plates are too buoyant to subduct. What happens to continental material when it collides? Since it has nowhere to go but up, this creates some of the world’s largest mountains ranges. Magma cannot penetrate this thick crust so there are no volcanoes, although the magma stays in the crust. Metamorphic rocks are common because of the stress the continental crust experiences. With enormous slabs of crust smashing together, continent-continent collisions bring on numerous and large earthquakes.”
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Divergent Plate Boundaries
“Divergent Plate Boundaries
Plates move apart at mid-ocean ridges where new seafloor forms. Between the two plates is a rift valley. Lava flows at the surface cool rapidly to become basalt, but deeper in the crust, magma cools more slowly to form gabbro. So the entire ridge system is made up of igneous rock that is either extrusive or intrusive. Earthquakes are common at mid-ocean ridges since the movement of magma and oceanic crust results in crustal shaking. The vast majority of mid-ocean ridges are located deep below the sea.”
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Transform Plate Boundaries
“Transform plate boundaries are seen as transform faults, where two plates move past each other in opposite directions. Transform faults on continents bring massive earthquakes.”
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Examples of plate boundaries
“A transform plate boundary between the Pacific and North American plates creates the San Andreas Fault, the world’s most notorious transform fault.
Just offshore, a divergent plate boundary, Juan de Fuca ridge, creates the Juan de Fuca plate.
A convergent plate boundary between the Juan de Fuca oceanic plate and the North American continental plate creates the Cascades volcanoes.”
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What type of stress is found at different plate boundaries
“Stress is the force applied to an object. In geology, stress is the force per unit area that is placed on a rock. Four types of stresses act on materials.
A deeply buried rock is pushed down by the weight of all the material above it. Since the rock cannot move, it cannot deform. This is called confining stress.
Compression squeezes rocks together, causing rocks to fold or fracture (break). Compression is the most common stress at convergent plate boundaries.
Rocks that are pulled apart are under tension. Rocks under tension lengthen or break apart. Tension is the major type of stress at divergent plate boundaries.
When forces are parallel but moving in opposite directions, the stress is called shear. Shear stress is the most common stress at transform plate boundaries”
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Strain or deformation
“When stress causes a material to change shape, it has undergone strain or deformation. Deformed rocks are common in geologically active areas.”
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