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Wegners theory of continental drift

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caleb morgan

on 13 December 2013

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Transcript of Wegners theory of continental drift

Caleb Morgan
Dr. turner
5th period

Theory of plate tectonics
The Theory that explains why and how continents move and the study of the formation of earths features
Wegners theory of continental drift
Alfred Wegner Proposed the idea that the continents were once a super continent ( all the Continents today formed together as one land mass) broke apart and slowly drifted apart into the positions they are in today
1.)Fossils-similarities along the coast line of each continent
2.) Rock formations-Ages and types of rocks in the coastal areas matched closely to that of other continents that are widely separated
3.) Climatic- geologist have discovered ancient glaciers in southern africa
Problems with Wegners Theory

The proposed mechanism the continents moved on ( plowing through the rock on the ocean floor) was easily dismissed by geologic evidence
Earths crust and rigid, upper part of the mantle

The lithosphere forms the thin outer shell of earth. It is broken into several blocks called tetonic plates, that ride on a deformable layer of mantle
is a layer of "plastic" rock just below just below the lithosphere

plastic rock is a solid rock layer that is under great pressure and flows very slowly , like putty does
How plates move
Mantle convection system - they move because of the intense heat in the Earth’s core that causes molten rock in the mantle layer to move. It moves in a pattern called a convection cell that forms when warm material rises, cools, and eventually sink down. As the cooled material sinks down, it is warmed and rises again
Three types of plate boundaries
Divergent Boundaries - two plates move away from each other

Convergent Boundaries - form when two plates collide

Transform Boundaries - two plates slide past each other
state of gravitational equilibrium between the earth's lithosphere and asthenosphere such that the tectonic plates "float" at an elevation which depends on their thickness and density
Isostatic Adjustments
When the plates loose/gain weight or mass and rise/sink in/out of the mantle
Enormous pressure put on the plates from constant heating and cooling of magma inside of the earth
Transform Boundary
Sea Floor spreading
Subduction zones
Oceanic + Oceanic crust
Continental + ocean crust
Volcano information
a mixture of molten or semi-molten rock, volatiles and solids that is found beneath the surface of the Earth,
Collision Zones
Continental + continental
When two oceanic plates collide, the younger of the two plates, because it is less dense,* will ride over the edge of the older plate

Earthquake Information
The elastic rebound theory is an explanation for how energy is spread during earthquakes. As rocks on opposite sides of a fault are subjected to force and shift, they accumulate energy and slowly deform until their internal strength is exceeded. At that time, a sudden movement occurs along the fault, releasing the accumulated energy, and the rocks snap back to their original undeformed shape.
Reverse Faults
Reverse faults are exactly the opposite of normal faults. If the hanging wall rises relative to the foot wall, you have a reverse fault. Reverse faults occur in areas undergoing compression (squishing). If you imagine undoing the motion of a reverse fault, you will undo the compression and thus lengthen the horizontal distance between two points on either side of the fault.

Strike-Slip Faults
are vertical (or nearly vertical) fractures where the blocks have mostly moved horizontally. If the block opposite an observer looking across the fault moves to the right, the slip style is termed right lateral; if the block moves to the left, the motion is termed left lateral
tends to pull something apart. It is the stress component perpendicular to a given surface, such as a fault plane, that results from forces applied perpendicular to the surface or from remote forces transmitted through the surrounding rock.
Sheer Stress
stress component parallel to a given surface, such as a fault plane, that results from forces applied parallel to the surface or from remote forces transmitted through the surrounding rock
Other Related Landforms
Dome Mountain
Hot spots
is the Process in which continents break apart

New small continents may form because of this

Scientist think as heat from the mantle builds up beneath the continent , the continental lithosphere becomes thinner and weaker eventually causing a rift to form
Super Continent Theory
Super Continent Cycle- The process in which super continents form and break apart
Pangaea - Super Continent that formed about 300 million years ago

Panthalassa - The single large oan that surrounded Pangaea
Pangaea and panthalassa
Terrane - piece of the lithosphere that has a unique geologic history that differ from the histories of the surrounding lithosphere

Accretion - a terrane becomes part of a continent at a convergent boundary

Part of a plate breaks off and becomes part of another plate
How plate movements alter climate and evolution
Climate - Geologic evidence shows that ice once covered most of the continental surface but once the Super continent broke apart and started to drift, global temperatures changed and much of the ice melted

Evolution- as continents rift or mountains form , populations of organisms are separated and even isolated and may evolve and adapt to their new enviroment
Divergent Boundary
A fault in which the hanging wall has moved downward relative to the foot wall.
Normal faults
The Process by which new oceanic lithosphere forms as magma and rises to the earth's surface and solidifies at a mid-ocean ridge
Pacific ridge
The study of the alignment of magnetic minerals in rock,
When two oceanic plates collide, the younger of the two plates, because it is less dense,* will ride over the edge of the older plate
When two plates slip past each other
systems of linear collapsed valleys caused by the movement of underlying salt layers toward the Colorado River canyon
can be formed from hot molten material (magma) rising from the Earth's mantle into the crust that pushes overlying sedimentary rock layers upward to form a "dome" shape.
Dome Mountain, New Mexico, near the Colorado boarder.
existed below the plates that would provide localized sources of high heat energy (thermal plumes) to sustain volcanism
Convergent Boundary
Folded mountain
the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other planet-like bodies. The field also includes studies of earthquake effects, such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, oceanic, atmospheric, and artificial processes (such as explosions
Seismograph - an instrument designed to measure and record vibrations in the earth
Focus - directly below the epicenter
Epicenter - point on the Earth's surface that is directly above the hypocenter or focus, the point where an earthquake or underground explosion originates
Normal faults in volcanic ashes and paleo-soils, El Salvador
Himalayas, asia
Seismic waves
Body waves
A body wave is a seismic wave that moves through the interior of the earth, as opposed to surface waves that travel near the earth's surface
primary waves
is a seismic body wave that shakes the ground back and forth in the same direction and the opposite direction as the direction the wave is moving
Surface Waves
are shear waves that are transverse in nature. These waves arrive at seismograph stations after the faster moving P waves during an earthquake and displace the ground perpendicular to the direction of propagation.
surface waves
are the waves that travel along the Earth's surface
The two principal types of seismic waves are P-waves (pressure; goes through liquid and solid) and S-waves (shear or secondary; goes only through solid - not through liquid). The travel velocity of these two wave types is not the same (P-waves are faster than S-waves). Thus, if there is an earthquake somewhere, the first waves that arrive are P-waves. In essence, the gap in P-wave and S-wave arrival gives a first estimate of the distance to the earthquake. As we know from physics, all waves change direction when they pass through layers of different density (refraction). That is what makes light collect in a magnifying glass, and that is also what makes seismic waves travel in curved paths through the Earth (because of the increasing pressure, materials are more dense towards the core, travel velocity of seismic waves increases). Refraction of seismic waves causes them to curve away from a direct path. Reflection causes them to glance off certain surfaces (e.g. core mantle boundary) when they hit it at too shallow of an angle. The result of this behavior, in combination with the fact that S-waves can not travel through liquids, is the appearance of seismic shadows, opposite of the actual earthquake site.
canyon lands, utah , USA
Fault Block Mountain
Yosemite valley Sierra Nevada
mountains are formed when large areas of bedrock is broken and forced up by tectonic shifts in the fault
North pacific ocean
Oceanic + oceanic

measure of the energy of an earthquake

measure of earthquake impact
Mercalli intensity scale
seismic scale used for measuring the intensity of an earthquake. It measures the effects of an earthquake, and is distinct from the moment magnitude
are waves of energy that travel through the Earth's layers, and are a result of an earthquake, explosion, or a volcano that imparts low-frequency acoustic energy
is a series of water waves caused by the displacement of a large volume of a body of water, generally an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explosions (including detonations of underwater nuclear devices), landslides, glacier calvings, meteorite impacts and other disturbances above or below water all have the potential to generate a tsunami.
3 conditions
1 when rock is heated.
2 when pressure released.
3 when rock changes composition.
refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling
Common locations
Along oceanic ridges
Ring of Fire
area where a large number of earthquakes and volcanic eruptions occur in the basin of the Pacific Ocean.
pyroclastic materials -are clastic rocks composed solely or primarily of volcanic materials
viscosity - Measure of a fluid and its resistance to gradual deformation by shear stress or tensile stress. For liquids, it corresponds to the informal notion of "thickness
There are three different metatypes of eruptions. The most well-observed are magmatic eruptions, which involve the decompression of gas within magma that propels it forward. Phreatomagmatic eruptions are another type of volcanic eruption, driven by the compression of gas within magma, the direct opposite of the process powering magmatic activity. The last eruptive metatype is the phreatic eruption, which is driven by the superheating of steam via contact with magma; these eruptive types often exhibit no magmatic release, instead causing the granulation of existing rock
Types of volcanoes
shield volcano is a type of volcano usually built almost entirely of fluid lava flows

A cinder cone or scoria cone is a steep conical hill of tephra (volcanic debris) that accumulates around and downwind from a volcanic vent

stratovolcano, also known as a composite volcano, is a conical volcano built up by many layers (strata) of hardened lava, tephra, pumice, and volcanic ash

caldera is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption. They are sometimes confused with volcanic craters.
Pyroclastic material
Erta ale
Shield Mountain
Mt. Hood ,Oregon
Composite Volcano
Cinder Cone Volcano
Veyo, Utah
Caldera Volcano
Mount Kaguyak , Alaska
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