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THE EARTH Interior Crust layer of rock that forms Earth’s skin includes dry land and ocean floor most places 5- 40 km thick in a few places, under mountains, can be as thick as 70 km similar to skin of onion Mantle made of hot rock, but solid nearly 3000km thick three regions: Lithosphere upper part similar to crust- rigid 100km Asthenosphere hotter and ↑ pressure like soft tar Lower Mantle Hotter, but still solid Core made mostly of iron and nickel two parts: liquid outer core solid inner core heat has melted metals in outer core pressure in inner core is so great molecules cannot spread out to the liquid formation this results in the metals being forced into the solid state recent evidence has shown inner core may contain O, S, Si Earth’s Magnetic Field believe that movement of liquid outer core creates magnetic field remember that Earth acts like a giant bar magnet the field around the magnet is the magnetosphere Convection is the flow that transfers heat within a fluid heating and cooling of the fluid, changes in the fluid’s density, and the force of gravity combine to set convection currents in motion these currents continue as long as heat is added Convection Convection in Earth in Earth’s mantle large amounts of heat are transferred by convection currents heat from the core and the mantle itself causes currents this rising and sinking happens over thousands/ millions of years there may also be currents in the outer core this plus the nickel and iron cause the magnet in the Earth Continental Drift in 1910 a German scientist, Wegener hypothesized that all the continents were once joined together in a single landmass and have since drifted apart •this idea that the continents/ crust moves is called CONTINENTAL DRIFT •the one continent has been called Pangaea •he gathered evidence from different areas to support his idea • Pangaea -All continents one land mass surrounded by ocean Evidence for Continental Drift He could see the evidence, but could not explain the way the earth’s crust moved. evidence is from: land features fossils climate change Land Features rocks and formations of rocks support the evidence of continental drift the theory of Pangaea rock formations in Africa (west) line up with one in South America (east) Brazil has coal fields with identical layers found in Africa Glacial erosion also exists in SA, Africa, India, and Australia that match similar patterns Fossils similar fossils have been found in SA and Africa Glossopteris is an extinct fern This fossil found in rocks approx 250 my old and is found in Africa, India, and Antarctica seeds from these plants were too large to be dispersed by wind from one continent to the other the seeds could only be dispersed in smaller areas like joined lands Climate Change salt, coal, and limestone support evidence that continents had very different climates long ago it is not due to climate change, but rather change in position of the lands today most salt deposits range from 10-30ْ latitude rock salt has been found in MI coal is only formed in warm swampy climates today coal deposits have been found in Antarctica limestone from coral reefs found in Texas and central US Wegener’s theory of Continental Drift was rejected at the time Other geologist acknowledged the evidence But they did not know or understand how the continents could move (no known mechanism) Lithosphere A portion of the earth that includes the crust and the upper part of the mantle that acts as one unit in its motion Can be different in its composition and softness Earth’s Layers Earth’s Upper Layers MOVEMENT OF THE CRUST Observation meets theory! Mid-Ocean Ridges cracks or vents found on the Earth’s crust of the ocean floor (oceanic crust) these areas rise above the surrounding crust underwater mountains, but most are under hundreds of meters below surface a few are above the water (island of Iceland, islands in the Philippines) underwater volcanoes discovered through sonar Sea Floor Spreading in 1960 Hess, an American geologist, proposed the sea floor spreads apart along both sides of a mid-ocean ridge as new crust is added the ocean floor is like a conveyor belt, carrying the continents along with them Mid-Ocean Ridge New crust being made Trenches if this theory is true the mid-ocean ridges produces new crust through volcanic eruptions and the floor spreads slowly at some point the floor (conveyor belt) must return at ocean trenches the crust undergoes SUBDUCTION subduction is the process by which ocean floor sinks beneath a deep-ocean trench and back into the mantle new oceanic crust is hot coming out of ridge, but it cools as it moves away and then sinks this takes ten of million of years because of this process the ocean floor is renewed every 200M years the Pacific Ocean is shrinking the Atlantic Ocean is growing see figure Evidence for Ocean Floor Spreading Molten Material Magnetic Stripes Drilling Samples Molten Material in 1960 a very small specialized sub, ALVIN, examined some ridges it found rocks shaped like pillows such rocks only form when material hardens quickly after erupting under water Magnetic Stripes earth is like a gigantic magnet oddly at times the poles reverse themselves last time 780,000 years ago the rocks in the oceanic crust made up of iron hold this record of the magnetic field as it comes out of ridge using sensitive instruments scientist can record the magnetic memory of the rocks the ocean floor shows stripes of these fields Drilling Samples Glummer Challenger, a drilling ship, sent drilling pipes through the water 6Km deep samples from sea floor were aged farther away from a ridge the samples were older youngest around a ridge Sea Floor Spreading Subduction Trench Subduction PLATE TECTONICS Putting it all together The Theory in 1965 a Canadian scientist, Wilson, discovered there are cracks in the continents similar to those on the ocean floor he saw the lithosphere was broken into pieces he called PLATES (both oceanic and continental plates) Wilson combined the knowledge of plates, seafloor spreading, and continental drift to come up with one unifying theory Plate Tectonics the theory of PLATE TECTONICS explains the formation, movement, and subduction of Earth’s plates pieces of Earth’s lithosphere are in slow constant motion driven by the convection currents of the mantle during subduction gravity pulls one edge of a plate down into the mantle the rest of the plate also moves as the plates move, collide, pull apart, or grind past each other amazing changes occur in Earth’s surface Earth’s Plates Plate Boundaries the edges of plates meet at plate boundaries, deep in lithosphere FAULTS occur at these points Faults are breaks in the Earth’s crust where rocks have slipped past each other (major points of earthquakes) Plate Boundaries there are three types of boundaries: Divergent Convergent Transform Divergent the point where two plates move apart most occur along mid-ocean ridges where sea-floor spreading occurs some do happen on land on land, a huge rift valley forms e.g. Great Rift Valley in Africa Convergent place where plates come together, collisions this results in a collision the density of plates will determine what will happen oceanic crust becomes cooler and denser as it spreads away from the mid-ocean ridge Pressure of water also condenses oceanic crust In general oceanic plates (OP) more dense than continental plates (CP) When 2 OP plates converge the denser sinks under the other less dense plate When OP and a CP collide, the OP is more dense than CP and will slide under the CP when 2 CP collide they are too close in densities for subduction instead the plates collide and squeeze the crust into huge mountain ranges Transform a place where two plates slip past each other no subduction occurs no crust is created or destroyed high earthquake activity at these points all this moving of the plates containing ocean and continents have shaped the surface of the Earth since its formation