Introduction
 Earth is a dynamic, ever-changing planet
 If we could go back in time 200 million yours ago there would be no Grand
Canyon or Himalayas
 More over we would find landmasses with unfamiliar shapes
 Earth scientist have shown that the landmasses are not fixed but slowly migrate across the globe
 Large landmasses have split apart resulting in the formation of oceans
 While the floor of the ocean has been recycled back into the Earth’s interior
 Separate landmasses collided and joined to form a larger continent
 The movement of earth outer rigid layer generates earthquakes
 Volcanoes, mountains, new ocean basins
 Moreover, the changing positions of the continents helps explain ancient climates and distribution of fossils
 The scientific theory which describes the mobile Earth is called plate tectonics
Continental drift
 A revolution in the Earth sciences begin in the early part of the twentieth century when a radical proposal was mad that the continents drifted about the face of Earth
 The development of this revolutionary hypothesis, known as continental drift, is credited to Alfred Wagener, a German meteorologist and geophysics
 Wegener proposed that a supercontinent, which he named Pangaea
 In addition, Wegener suggested that this supercontinent began breaking into smaller landmasses, which drifter to their present position
 Fit of the Continents
 Fossil evidence
 Evidence from Rocks
 Paleoclimatic Evidence
 Wegener first suspected that the continents might have been joined when he noticed the similarities of the coast line of Africa and South America
 South America and Africa
Fossil Evidence
 Scientist have discovered that fossils of the same ancient plants and animals were found on widely separated continents
 Why ore fossils of Mesosaurus found on both sides of the South Atlantis but nowhere else in the world
 Three ideas were proposed to explain the distribution of the fossils

 Rafting, stepping stone islands, and land bridges
 Wegener had a better explanation- he proposed the continent of supercontinent Pangaea
Evidence from rocks
 When working a jigsaw puzzle every
 The picture must be continuous as well
 The picture that must be matched in the continental drift puzzle is represented by ricks of similar types
 And mountain belts
 Mountains of about the same age
 The mount ranges such as the appellation mountain
Paleoclimatic evidence
 Earth science have learned that between 220 and 300 million years ago vast ice sheets covered extensive portions of earth’s landmasses
 Evidence called till glaciers leave behind
 An unsorted mixture of many different sediment sizes
 Below these layer of till lay bedrock that was scratched and polished by glaciers armed
 Most glaciers are in an area that you wouldn’t expect
 Scientist have rejected the idea of the equator becoming cold because during this period large tropical swamps existed in the Northern Hemisphere
 The lush tropical of these lush swamps eventually became the major coalfields of the eastern United States and Europe.
 If the coal is under enough pressure the coal will turn in to a diamond
 Fossils from the coal fields indicate that the environment trees had large fronts
 Scientist realized that the area containing swamp areas and glacier areas when put together are all in one spot
The Great Debate
 Wegener’s continental drift began to attracted attention in 1924
 The continents didn’t break through the ocean floor
 Harold Jefferson said that the ground under water got softer and moved little by little

Continental drift and Paleomagnitism
 The imputes for renewed interest in continental drift came from studies conduct to determine the intensity of direction
 Any one who has used a compass knows that Earth’s magnetic fields has a north pole and a south pole that align closely but not exactly
 Earth’s magnetic field is similar to that produced by a simple bar magnet.
 The technique used to study ancient magnetic field relies on the fact that some rocks contain iron rich minerals serve as fossil compass
 Magnetite is found in basaltic rich rocks
 Magnetic alignment in older lava fields was found to vary widely
 In The past 500 years the magnetic pull has moved
 Either the poles had migrated or the continents shifted
 Poles have remained fixed yet the plates are moving
 The polar magnetism this alone proved that Pangaea did exist because the lava magnetism created
Seafloor spreading
 One reason that Wagener’s continental drift hypothesis was not widely accepted because there was not much known of the ocean floor
 The war ships gave echolocation in 1950-1960 as new echolocation sounding technology was developed
 An echo sounder measures the sound in time and can tell how far is the ocean bottom
 1500 meters per second
 Extensive sampling of the ocean floor did not recover material that was older than 200 million years in age
 Ridges proposes that ridges are located above upwelling portions of large convection cells in the mantle
 As rising material spreads laterally seafloor is carried
 As the crust is pulled apart, molten rock intrudes the fractures
 Older portions of the seafloor are gradually consumed as they descend into the mantle
Plate tectonics: the new paradigm
 According to the plate tectonics model, the uppermost mantle along with the overlying crust, behaves as a strong, ridged layer known as the lithosphere
 This rigid outer shell overlies a weaker region in the mantle known as the asthenosphere
 The temperature and pressure regime in the upper asthenosphere results in a very weak zone that permits the lithosphere to be effectively detached from the layers below.

 Thus the weak rock within the upper asthenosphere allows Earth’s rigid outer shell to move
 The lithosphere is broken into numerous segments, called plates, that are in motion with respect to one another, thereby continually changing shape and size
 Seven major lithospheric plates are recognized
 South American plate
 North American plate
 Pacific plate
 Australian- Indian plates
 Antarctic plate
 Eurasian plate
 And African plate
 The largest is the Pacific plate which encompasses a significant portion of the
Pacific Ocean basin
 Most of the large plates include an entire continent plus a large area of ocean floor.
 Intermediate size plate include
 Philippian plate
 Arabian plate
 Scotia plate
 Caribbean plat
 Nazca plate
 Cocos plate
 And Juan de Fuca plate
 Interactions of the plates sre n there boundaries
 There are three types of plate boundaries
 Divergent plate boundaries where two plates move apart resulting in upwelling of material from the mantle the create new seafloor
 Convergent plate boundaries: where two plates move together, resulting in oceanic lithosphere descending beneath an overriding plate, eventually to be reabsorbed into the mantel
 Although the total surface area of Earth does not change
 The individual plate may diminish or grow in size
 The Antarctic plate is mostly bounded by divergent boundaries and is growing larger
 The pacific plate is shrinking
 The African plate will eventually split
 Every plate has all three plate boundaries
Divergent plate boundaries
 Most divergent plate boundaries are located along the crest of oceanic crust

Oceanic ridges
 Along a well developed divergent plate boundaries the sea floor is elevated forming the oceanic ridge
 The oceanic ridge represents 20% of Earth’s surface
 The ocean ridge can be 1000 to 4000 km wide
 Along the axis of some ridges segments is a deep down faulted stretch called a rift valley
 The average spreading is 5 cm slow is 2cm
 The oldest ocean floor is 200 million years old
 The ocean is growing symmetrically
Continental rift
 Spreading centers mostly under water
 Continental rifting =extensional forces, up warping
 Faulting the rift is up warping the rift valley creating a continent like the Red sea
 Also like lake Victoria
Earth’s interior 2/6/13
 Heat from the Earth’s interior is the major source of energy for the movement of Earth’s outer shell
 Scientist have determined the Earth’s interior is divided into four layers
 The inner core is a solid iron rich sphere having a diameter of 2432 kilometers (1511 miles)
 The outer core is a liquid metallic layer that is about 2270 km (1410 miles)
 Earth’s magnetic field is thought to be generated by vigorous churning of the iron-rich material in the hot, fluid outer core. Movement of outer core creates the magnetic field.
 The mantle is a solid rocky layer having a thickness of about 2885km (1789 miles.
 Over 82 percent of Earth’s volume is contained within the mantle, a thick shell of rock composed of silicate materials that are rich in iron and magnesium
 The outer crust is a very thin outer layer that ranges from 7-70km
 The crust is made up of two crusts oceanic (basalt) and continental (granite)
 The continental crust is about 35-70 km
 Oceanic crust is about 7km (5 miles)
 Continental rocks are less dense than oceanic crust
 There is an Asthenosphere and a lithosphere
 Asthenosphere is located within the upper mantle between 100 to 600 km and is composed of hot rocky material that the movment is very slow
 The lithosphere is part of the crust and goes lower
 Behaves as a strong ridged layer because it is composed of solid rock

 Weak rock allows the ridged outer shell to move
Convergent plate boundaries 2/27/13
 Convergent plate margins occur where two plates collide and the motion is accommodated by on plate sliding under
 Also called Subduction zones because the lithosphere is descending in to the asthenosphere
 Deep ocean trenches develop between two convergent plates
 The oceanic plate is more dense than the continental plate so the plate descend in to the asthenosphere
 Some oceanic plate descends fairly beep sometimes
 Density of the plate is what determines which goes under (more compact and temperature change)
 As it gets older the oceanic plate will more likely sink because it is more cool
 Older oceanic plate will descend almost 90 degree because of the density
 as one is decending the plate pulls the continent with it. It changes position.
 There are three types of convergent boundaries
 Oceanic and oceanic
 Oceanic and continental
 Continental and continental

Oceanic continental convergence
 When the oceanic lithosphere go 100 km the plate rock starts to melt
 Peridotite has low water content
 Different amounts of water in rock effects how it melts
 Seismic evidence predicts that under average conditions of temperature and pressure the upper mantle consists of solid
 There are different depths to melt different times
 100 km melts wet peridotite at roughly 400 degrees
 Hot mixture gradually rises toward the surface in tear shape form
 Basaltic magma separates from the un-melted components and continues to ascent
 Basaltic magma rises to the surface because it is less dense and hot
 Magma sometimes melt other continental rock
 Andesitic magma reaches the surface they erupt explosively generating large columns of ash
 Andesitic rock name came from the Andes mountains in south America