Part 2 Plate Tectonics

Sculptors of the Earth : 

Sculptors of the Earth Plate Tectonics

The Idea : 

The Idea In 1915 Alfred Wegener, a German scientist, proposed the idea of continental drift The theory proposed that the continents had once been joined to form a single supercontinent The supercontinent was called Pangaea which means “all land”

The Idea : 

The Idea

The Idea : 

The Idea

The Idea : 

The Idea

The critics : 

The critics Wegener got his idea when he noticed how many continents looked like puzzle pieces that could be put together However, this was not enough to convince others who correctly stated that erosion continually changes shorelines over time

The Evidence : 

The Evidence Matching Fossils This includes several fossil organisms found on different landmasses Prime example is the Mesosaurus found in western Africa and Eastern South America

The Evidence : 

The Evidence If Mesosaurus had been a good enough swimmer to change continents, then its remains should have been more widespread instead of just being found in what could have one time been a single area

The Evidence : 

The Evidence Rock types and structures This evidence can be found in the form of several mountain belts that end on one coastline and then reappear on a landmass across the ocean An excellent is Appalachian mountains in USA that disappear in Newfoundland and then reappear in the British Isles and Scandinavia The now separate mountain ranges have been found to be of the same age with similar rocks and structures showing they were once the same range

The Evidence : 

The Evidence

The Evidence : 

The Evidence Ancient Climates Wegener found glacial deposits showing that between 200 and 300 million years ago ice sheets covered large areas of the southern hemisphere Layers of glacial till were found in southern Africa, South America, India, and Australia Many of these areas now lie near the equator!

The Evidence : 

The Evidence While ice was covering areas that are now near the equator, areas that are now not near the equator had lush jungle forestation In what is now the northern hemisphere, evidence has been found to show the areas had lush vegetation, and swamps These areas became part of the coal we now mine in places like Pennsylvania

The Evidence : 

The Evidence

The Evidence : 

The Evidence Paleomagnetism As lava cools, it becomes magnetized parallel to the magnetic field The discovery of strips of alternating polarity, which lie as mirror images across the ocean ridges, is among the strongest evidence of seafloor spreading

The Evidence : 

The Evidence Scientists have found a close link between deep-focus earthquakes and ocean trenches as well as the absence of deep-focus earthquakes along the oceanic ridge system

The Evidence : 

The Evidence Ocean drilling Core samples have shown that the crust nearest to ocean ridges is the youngest, while the oldest is near the continental margins

The Evidence : 

The Evidence Hot Spots Hot spots support the idea that the plates move over the Earth’s surface and show the direction of the movement Prime example is the Hawaiian Island chain

The Evidence : 

The Evidence

The Evidence : 

The Evidence Later, with new technologies that allowed us to map the ocean floors, collect data on earthquakes, and on the magnetic field, a new theory arose Plate tectonics Proposes that Earth’s outer shell consists of individual plates that interact in various ways and thereby produce earthquakes, volcanoes, mountains, and the crust itself

Plate Tectonics : 

Plate Tectonics

Plate Tectonics : 

Plate Tectonics There are three main types of plate boundaries Divergent boundaries Convergent boundaries Transform fault boundaries

Plate Tectonics : 

Plate Tectonics Divergent boundaries Plates spread apart Results in the upwelling of material from the mantle to form new lithosphere

Plate Tectonics : 

Plate Tectonics Creation of new lithosphere produces new sea floors or

Plate Tectonics : 

Plate Tectonics It can separate land areas

Plate Tectonics : 

Plate Tectonics Convergent Boundaries Two plates move toward each other An ocean plate can move toward an ocean plate An ocean plate can move toward a continental plate A continental plate can move toward another continental plate

Plate Tectonics : 

Plate Tectonics Creations of convergent boundaries Subduction zones are areas where an oceanic plate is forced under another plate and into the mantle Ocean plate to ocean plate Ocean trenches created as well as volcanic island arcs Aleutian Islands in Alaska Oceanic plate to continental plate Oceanic trenches created as well as continental volcanic arcs and associated mountains Continental plate to continental plate Creates complex mountains Himalayas and Rockies

Plate Tectonics : 

Plate Tectonics

Plate Tectonics : 

Plate Tectonics Transform fault boundaries Two plates grind past each other without the production or destruction of lithosphere

Plate Tectonics : 

Plate Tectonics Most transform faults are found in the oceans, but a few are on land such as the San Andreas fault With time the western California side of the fault will become an island off the coast and eventually reach Alaska

Plate Motion : 

Plate Motion What causes the plates to move? Convection occurring in the mantle is the basic driving force for plate movement Unequal distribution of heat within the Earth causes the thermal convection in the mantle that drives the plate movement

Plate Motion : 

Plate Motion Two other methods which work together are called Slab-Pull and Ridge Push Ridge Push As magma is exposed in ridges at the surface and cools, this pushes the plates apart Slab Pull As the dense oceanic crust is subducted under another plate, it pulls the slab (plate) along with it Gravity is the key force in this method

50,000,000 years from now : 

50,000,000 years from now