1 History – Abraham Ortelius • In the 1500’s a Dutch mapmaker, Abraham Ortelius noticed the continents across the Atlantic Ocean fit together like a puzzle. • He proposed that North America and South America had separated from Europe and Africa by earthquakes and floods. Abraham Ortelius’ Map 2 3 History – Edward Suess • Edward Suess was an, Austrian geologist, in the late 1800’s, proposed the southern continents had once been joined together in a single landmass. • He named this Gondwanaland. 4 Gondwanaland 5 History – Alfred Wegener • In 1912 a German meteorologist, Alfred Wegener, had an idea about continental movement. • His hypothesis was called Continental Drift. 6 History – Alfred Wegener • His hypothesis proposed that the continents had once been joined as a single landmass, called Pangaea. • “Pangaea” is a Greek word meaning “all the Earth” 7 Pangaea 8 History – Alfred Wegener • Wegener believed that Pangaea began to break apart 250 million years ago. • The continents have been continuously moving since then to where they are today. 9 Wegener’s Evidence – Rocks • Believed there should be similar rock types on opposite sides of the Atlantic Ocean. • Appalachian Mountains are very similar to the Scottish Highlands. • Rocks in Brazil matched those in Africa, with a similar age of around 2.2 billion years old. 10 Wegener’s Evidence – Rocks 11 Wegener’s Evidence - Fossils • Plants Seeds too heavy to blow across the ocean Seeds too fragile to float across the ocean • Animals – Land animals could not swim – Freshwater animals could not swim in the ocean (salt water) – Couldn’t have evolved the same way in two different locations. Wegener’s Evidence – Fossils 12 13 Wegener’s Evidence – Climate • Glacier deposits found in Africa, India, Australia, and South America Wegeners Skeptics 14 • Many scientists rejected Wegener’s hypothesis because he could explain what happens in continental drift, but he could not explain… HOW DO THE CONTINENTS MOVE??? 15 History – Arthur Holmes • In 1929 a geoscientist, Arthur Holmes, proposed that convection occurred in the mantle. • This convection could push and pull plates together or apart. • Still NO evidence! 16 Heat Transfer • There are three main ways that heat can be transferred: – Conduction – Convection – Radiation • Have you ever burned your hand on the stove or a curling iron? – Is it different than getting a sunburn? Conduction 17 • Conduction = the transfer of heat as a result of direct contact • This is the reason you get burnt when touching the hot stove or curling iron. Convection 18 • Convection = the transfer of heat through the physical movement of the heated substance. • As the water is heated the molecules move faster and farther apart, making the fluid less dense, and forcing it to move to the top. – What happens when the fluid cools? 19 Radiation • Radiation = the transfer of heat in the form of electromagnetic waves. • This is the reason why when standing near a campfire your front side feels warm, but your backside is cold. • This is also the type of heat transfer that occurs when you get sunburns in the summertime. 20 History – Harry Hess • Harry Hess was a professor of geology and developed the seafloor spreading hypothesis. • He used paleomagnetism and seafloor mapping to help prove convection currents as a source for “continental drift” Finding Evidence 21 • Scientists first tried to map the ocean floor by using sonar. – A device that bounces sound waves off terrain at the bottom of the ocean. These waves bounce back and depending on how long the waves travel we can determine the depth. • The invention of the Magnetometer – A device that detects small changes in the magnetic field in rocks on the ocean floor. Magnetometer and Sonar 22 23 Seafloor Spreading • In the early 1960’s Harry Hess suggested that seafloor spreading causes new rock to form on our ocean floor. • Seafloor Spreading = the process by which molten material adds new oceanic crust to the ocean floor • Seafloor Spreading and Magnetic Reversals 24 Mid Atlantic Ridge 25 Paleomagnetism • Paleomagnetism = the study of Earth’s magnetic field through rocks, clay, and sediments. • Periodically, Earth’s magnetic field reverses polarity. These reversals have occurred at random points in Earth’s history. • Scientists can study rocks with iron-bearing minerals at the bottom of the oceans to see the alignment of Earth’s magnetic field. 26 PROOF 27 • This proved that new sea floor was being created at mid-ocean ridges. • Through paleomagnetism scientists discovered there are identical magnetism on opposite sides of the ridges. • Paleomagnetism/Seafloor Spreading • Finally, we have PROOF!!! Quick Recap 28 • 1500 – Abraham Ortelius suggests continents look like puzzle pieces. • 1800 – Edward Suess suggests the southern continents were once connected and called Gondwanaland. • 1912 – Alfred Wegener suggests a hypothesis called continental drift, claiming all the continents at one time were connected in a supercontinent, Pangaea. • Bill Nye on Sea Floor Spreading • https://www.youtube.com/watch?v=GyMLlLx bfa4 Quick Recap 29 • 1929 – Arthur Holmes suggested that convection occurred in Earth’s mantle and could drive the movement of plates. • 1960 – Harry Hess develops the seafloor spreading hypothesis and finally gives proof for continental drift. 30 Plate Tectonics • Plate Tectonics = a theory that describes the large scale movements of Earth’s lithosphere • The theory of plate tectonics was built on the ideas of continental drift and seafloor spreading. • Earth’s lithosphere is broken down into 8 large plates and several smaller plates that move in different directions and at different speeds. 31 Types of Boundaries • Plate Boundaries = places where two or more plates interact in the lithosphere of Earth • There are three basic types of boundaries: – Divergent – Convergent – Transform 32 Divergent Boundaries • Divergent boundary = plates move away from one another • Most of these boundaries are situated along mid ocean ridges. • The typical spreading rate is about 5 cm/year, but can range from 2-20 cm/year 33 Divergent Boundaries • Continental crust can begin to rift from upward movement of hot rock from mantle. • Uplift results in extension that stretches the crust. Divergent Boundaries 34 • Extension of the crust is accompanied by episodes of faulting and volcanism. • This results in rift valleys like the East African Rift Valley. 35 East African Rift Valley DIVERGENT EAST AFRICAN RIFT Divergent Boundaries 36 • As the spreading continues, the rift valley will widen and deepen, extending out to the sea. • The valley then becomes a narrow linear sea – Red Sea, Gulf of California 37 Divergent Boundaries • The rifting will continue until a full blown ridge system is created forming an ocean basin – Atlantic Ocean 38 Convergent Boundaries • Convergent boundary = plates move into or collide with one another • There are three forms of convergent boundaries: 1. Oceanic Crust - Continental Crust Collisions 2. Oceanic Crust - Oceanic Crust Collisions 3. Continental Crust - Continental Crust Collisions Ocean – Continent Collision 39 • Denser oceanic crust is subducted forming a trench and volcanoes. ANDES MOUNTAINS CONVERGENT Andes Mountain Range 40 Andes Mountain Range 40 Oceanic Crust – Oceanic Crust 41 Collision • Similar to oceanic – continental collisions except that volcanoes can form islands Mariana Trench 42 MARIANAS TRENCH CONVERGENT Continental Crust– Continental Crust 43 Collision • Usually preceded by subduction until continents smash into one another. • Results in thickening of crust forming very high mountains. Himalayan Mountains 44 Himalayan Mountains 44 HIMALAYAN CONVERGENT MOUNTAINS Transform Boundaries 45 • Transform boundary = plates grind past one another • A great example of this is the San Andreas Fault in California. 46 San Andreas Fault SAN ANDREAS FAULT TRANSFORM 46 San Andreas Fault 36 History • http://www.slideshare.net/gp c2717/plate-tectonics-history- and-boundaries • http://www.imaginiquebengal s.com/condriplatec.pdf.