Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Geomorphology wikipedia , lookup
Spherical Earth wikipedia , lookup
Post-glacial rebound wikipedia , lookup
History of geomagnetism wikipedia , lookup
History of Earth wikipedia , lookup
Oceanic trench wikipedia , lookup
Age of the Earth wikipedia , lookup
History of geology wikipedia , lookup
Mantle plume wikipedia , lookup
Plate Tectonics Table of Contents Earth’s Interior Convection and the Mantle Drifting Continents Sea-Floor Spreading The Theory of Plate Tectonics Plate Tectonics - Earth’s Interior Exploring Inside the Earth • Earth’s surface is constantly changing. It looks very different today than it did millions of years ago. • Geologists (scientists who study rocks) would have to dig down 6,000 kilometers to get to the Earth’s core. • Because this would be impossible, geologists use two main types of evidence to learn about Earth’s interior Plate Tectonics - Earth’s Interior Exploring Inside the Earth – Direct evidence – from rock samples – Indirect evidence – from seismic waves. Plate Tectonics - Earth’s Interior Exploring Inside the Earth • Seismic waves – vibrations that travel through Earth carrying the energy released during an earthquake. – Can detect the structure of the planet by studying the speed and path of the waves – Determined that the Earth is made up of many layers Plate Tectonics - Earth’s Interior A Journey to the Center of Earth • The three main layers of Earth: – crust, the mantle, and the core. – Layers vary greatly in size, composition, temperature, and pressure. • Temperature – the heat is a result of the formation of the planet and radio active materials. – Increases by about 1°C every 40 meters down Plate Tectonics - Earth’s Interior A Journey to the Center of Earth • Pressure – force exerted on a surface divided by the area over which the force is exerted. – Increases as you go deeper into the Earth Pressure increases the deeper you go, like that of a swimming pool Plate Tectonics - Earth’s Interior The Crust • Crust – layer of rock that forms Earth’s outer skin – Includes both dry land and the ocean floor. – Thinnest at ocean floors and thickest at mountains Plate Tectonics - Earth’s Interior The Crust • Two types of crust: – Oceanic crust – the crust that makes up the ocean floor • Made mostly of basalts – dark rock with a fine grained texture – Continental crust – the crust that makes up the continents • Made mostly of granites – light rock with a coarse grained texture Plate Tectonics - Earth’s Interior The Mantle • Mantle – layer of hot semi-solid rock under the crust – Divided into layers based on the physical characteristics – Total about 3,000 km thick Plate Tectonics - Earth’s Interior The Mantle • Two parts to the upper mantle: • Lithosphere –where the upper most part of the mantel and the crust merge – “lithos” Greek for “stone” – About 100 km thick • Asthenosphere – under the lithosphere where rock is heated causing it to be flexible (like plastic) – “asthenes” Greek for “weak” – Still considered a solid Plate Tectonics - Earth’s Interior The Core • Lower mantle – beneath the asthenosphere, very hot solid material • Core – in the center of Earth and made mostly of iron and nickel – Consists of two parts: outer and inner – Total 3,486 km thick • Outer core – molten liquid metal – Scientists think that movements in the liquid outer core create Earth’s magnetic field. • Inner core – dense ball of iron and nickel atoms – So much pressure that it remains a solid Plate Tectonics - Earth’s Interior The Core • The core is made mostly of the metals iron and nickel. It consists of two parts–a liquid outer core and a solid inner core. Plate Tectonics - Earth’s Interior Temperature Inside the Earth • The graph shows how temperatures change between Earth’s surface and the bottom of the mantle. On this graph the temperature at the Earth’s surface is 0oC. Study the graph carefully and then answer the questions. Plate Tectonics - Earth’s Interior Temperature Inside the Earth • Reading Graphs: As you move from left to right on the x-axis, how does depth inside the Earth change? The depth increases. Plate Tectonics - Earth’s Interior Temperature Inside the Earth • Estimating: • What is the temperature at the boundary between the lithosphere and the asthenosphere? About 1,600oC Plate Tectonics - Earth’s Interior Temperature Inside the Earth • Estimating: What is the temperature at the boundary between the lower mantle and the core? About 3,200oC Plate Tectonics - Earth’s Interior Temperature Inside the Earth • Interpreting Data: How does temperature change with depth in Earth’s interior? It generally increases with depth. Plate Tectonics - Earth’s Interior Links on the Structure of Earth • Click the SciLinks button for links on the structure of Earth. Plate Tectonics - Convection and the Mantle Types of Heat Transfer • Heat always moves from a warmer substance to a cooler substance. – Ex: holding an ice cube in your hand • There are three types of heat transfer: radiation, conduction, and convection. Plate Tectonics - Convection and the Mantle Radiation • Radiation – the transfer of energy through space – takes place with no direct contact between a heat source and an object – Ex: Sunlight Plate Tectonics - Convection and the Mantle Conduction • Conduction – the transfer of heat within a material or between materials that are touching – Ex: spoon in a pot of hot soup In conduction, the heated particles of a substance transfer heat through contact with other particles in the substance. Plate Tectonics - Convection and the Mantle Convection • Convection is caused by differences of temperature and density within a fluid. • Density – measure of how much mass there is in a volume of a substance. – Ex: A rock is more dense than the same volume of water. • As a substance is heated, molecules spread apart, causing it to be less dense, and allowing it to rise • As it cools the molecules get closer together, increasing density, and causing gravity to pull it back down. Plate Tectonics - Convection and the Mantle Convection Currents • Heating and cooling of the fluid, changes in the fluid’s density, and the force of gravity combine to set convection currents in motion. Plate Tectonics - Convection and the Mantle Convection Currents • Convection current – movement of a fluid, caused by differences in temperature, that transfers heat from one part of the fluid to another. – Continue as long as heat is added – Without heat, convection currents eventually stop. Plate Tectonics - Convection and the Mantle Convection Currents in Earth • Heat from the core and the mantle itself causes convection currents in the mantle. Plate Tectonics - Convection and the Mantle Mantle Convection • Click the Video button to watch a movie about mantle convections. Plate Tectonics - Convection and the Mantle More on Convection Currents in the Mantle • Click the PHSchool.com button for an activity about convection currents in the mantle. Plate Tectonics - Drifting Continents Continental Drift • Throughout centuries people have been studying maps. During this time many people have noticed the similarities between the coastlines of the continents. • The continents on each side of the Atlantic Ocean looked as though they could fit together like a puzzle piece. Plate Tectonics - Drifting Continents Continental Drift • Alfred Wegener – (1910) German scientist who hypothesized that all of the continents were once joined together in a giant continent that he named Pangaea. – Continental drift theory - idea that the continents slowly move across Earth’s surface – Pangaea was believed to exist about 300 million years ago when reptiles and winged insects first appeared Plate Tectonics - Drifting Continents Continental Drift • Wegener’s hypothesis was that all the continents were once joined together in a single landmass. Plate Tectonics - Drifting Continents Continental Drift • Wegener gathered three types of evidence to support his ideas about continental drift. – They included: land features, fossils, and evidence of climate change • Evidence from land features – Wegener found that the mountains of eastern South America matched that of western Africa – Coal in England matched that of eastern North America Plate Tectonics - Drifting Continents Continental Drift • Evidence From Fossils • Wegener also used fossils to support his idea. • Fossil – any trace of an ancient organism that has been preserved in rock. – Ex: Glossopteris (250 mill yr old fern) – found in rocks of Africa and South America Plate Tectonics - Drifting Continents Continental Drift – Ex: Mesosaurus and Lystrosaurus (ancient freshwater reptiles) now separated by an ocean • Evidence From Climate – Wegener found fossil evidence of ancient tropical plants and animals in polar regions – He also found evidence of ancient arctic species in areas that are now close to the equator. Plate Tectonics Evidence for Continental Drift Plate Tectonics - Drifting Continents Evidence for Continental Drift Plate Tectonics - Drifting Continents Wegener’s Hypothesis Rejected • Many scientists opposed Wagener’s hypothesis, despite the evidence, because he was unable to explain what the force was that caused this movement. Plate Tectonics - Drifting Continents Links on Continental Drift • Click the SciLinks button for links on continental drift. Plate Tectonics - Sea-Floor Spreading Mid-Ocean Ridges • The East Pacific Rise is just one of the many mid-ocean ridges that wind beneath Earth’s oceans. Plate Tectonics - Sea-Floor Spreading Mid-Ocean Ridges • Mid-ocean ridge – undersea mountain chain where new ocean floor is produced – Discovered by using sonar (a device that bounces sound waves off underwater objects and then records the echoes) • Harry Hess – (American) first geologists to study mid-ocean ridges – Found evidence to back up Wegener’s Continental Drift Theory – Called this seafloor spreading Plate Tectonics - Sea-Floor Spreading What Is Sea-Floor Spreading? • Sea-floor spreading – sea floor spreads apart along both sides of a mid-ocean ridge as new crust is added – Ocean floors move like conveyor belts, carrying the continents along with them. Plate Tectonics - Sea-Floor Spreading Evidence for Sea-Floor Spreading • Hess found evidence to support his theory of seafloor spreading, which included: – eruptions of molten material, magnetic stripes in the rock of the ocean floor, and the ages of the rocks themselves. Plate Tectonics - Sea-Floor Spreading Evidence for Sea-Floor Spreading • Evidence From Molten Material – 1960’s – submarine Alvin found rocks along the ocean floor running parallel with the ridge – These type of rocks only form when molten material hardens quickly after erupting under water • Evidence From Magnetic Stripes – rock that makes up the ocean floor lies in a pattern of magnetized “stripes.” – record of reversals in Earth’s magnetic field. Plate Tectonics Evidence for Sea-Floor Spreading • Evidence From Drilling Samples – Glomar Challenger – (1968) drilling ship that obtained rock samples from the ocean crust – Found that the rocks closest to the midocean ridge were “younger.” – The farther away from a ridge the samples were taken, the older the rocks were Plate Tectonics Subduction at Trenches • Deep-ocean trench – deep valley along the ocean floor beneath which oceanic crust slowly sinks toward the mantle. – The oceanic crust bends downward into the mantle • Subduction – process by which oceanic crust sinks beneath a deep-ocean trench and back into the mantle. – Occurs at a convergent plate boundary Trench Subduction Plate Tectonics - Sea-Floor Spreading Subduction at Trenches • In a process taking tens of millions of years, part of the ocean floor sinks back into the mantle through deep-ocean trenches. Plate Tectonics - Sea-Floor Spreading Growing an Ocean • Because of seafloor spreading, the distance between Europe and North America is increasing by a few centimeters per year. Plate Tectonics - Sea-Floor Spreading More on Sea-Floor Spreading • Click the PHSchool.com button for an activity about sea-floor spreading. Plate Tectonics - Sea-Floor Spreading Sea-Floor Spreading • Click the Video button to watch a movie about sea-floor spreading. Plate Tectonics How Plates Move • Plate tectonics – theory that pieces of Earth’s lithosphere are in constant motion, driven by convection currents in the mantle. – As the plates move, they collide, pull apart, or grind past each other, producing spectacular changes in Earth’s surface. – Changes include volcanoes, mountain ranges, and deep-ocean trenches. Plate Tectonics - The Theory of Plate Tectonics How Plates Move • The theory of plate tectonics explains the formation, movement, and subduction of Earth’s plates. Plate Tectonics Plate Boundaries • The edges of Earth’s plates meet at plate boundaries that extend deep into the lithosphere. • Fault – break in Earth’s crust where masses of rock slip past each other. Plate Tectonics - The Theory of Plate Tectonics Plate Boundaries • There are three kinds of plate boundaries: – divergent boundaries, convergent boundaries, and transform boundaries. – A different type of plate movement occurs along each type of boundary. Plate Tectonics - The Theory of Plate Tectonics Calculating a Rate • To calculate the rate of plate motion, divide the distance the plate moves by the time it takes to move that distance. Rate = distance/time • For example, a plate takes two million years to move 156 km. Calculate its rate of motion. • 156 km/2,000,000 years = 7.8 cm per year Plate Tectonics - The Theory of Plate Tectonics Calculating a Rate • Practice Problem • The Pacific plate is sliding past the North American plate. It has take ten million years for the plate to move 600 km. What is the Pacific plate’s rate of motion? • 60,000,000cm ÷ 10,000,000years = 6 cm/yr Plate Tectonics - The Theory of Plate Tectonics Plate Boundaries • Divergent boundary – plate boundary where two plates move away from each other. – Most divergent boundaries occur along the mid-ocean ridges where sea-floor spreading occurs. – Rift valley – deep valley that forms where two plates move apart. • Ex: Great Rift Valley in Africa Plate Tectonics - The Theory of Plate Tectonics Plate Boundaries • Convergent boundary – plate boundary where two plates move toward each other. – The density of the plates determines which one comes out on top. – Ex: Oceanic – Continental collision: • Oceanic crust is more dense, therefore subduction occurs – Ex: Continental – Continental collision: • Neither is more dense, therefore mountains form Ex: Appalachia Mountains Plate Tectonics - The Theory of Plate Tectonics Plate Boundaries • Transform boundary – plate boundary where two plates move past each other in opposite directions. – Earthquakes often occur along transform boundaries, but crust is neither created nor destroyed. Ex: San Andreas Fault, California Plate Tectonics - The Theory of Plate Tectonics Continental Drift • It has taken the continents about 225 million years since the breakup of Pangaea to move to their present locations. Plate Tectonics - The Theory of Plate Tectonics Continental Drift Activity • Click the Active Art button to open a browser window and access Active Art about continental drift. Plate Tectonics Graphic Organizer Type of Boundary Transform boundary Convergent boundary Divergent boundary Type of Motion Plates slide past each other. Plates move together. Plates move apart. Effect on Crust Crust is sheared. Subduction or mountain Feature(s) Formed Strike-slip fault Mountains, volcanoes Mid-ocean Crust pulled apart ridge, ocean floor