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
History of geomagnetism wikipedia , lookup
Post-glacial rebound wikipedia , lookup
Geochemistry wikipedia , lookup
Age of the Earth wikipedia , lookup
Abyssal plain wikipedia , lookup
History of geology wikipedia , lookup
Tectonic–climatic interaction wikipedia , lookup
Oceanic trench wikipedia , lookup
Mantle plume wikipedia , lookup
The Structure of the Earth & Plate Tectonics Restless planet What is the theory of plate tectonics? The Theory of Plate Tectonics states that the continents have moved and are still moving…about as fast as your fingernails grow. In 1912, Alfred Wegener introduced a hypothesis of continental drift, but he did not fully understand what caused the plates to move. As scientists amassed more data, Wegener’s hypotheses was amended to become the Plate Tectonic Theory. A theory is an explanation of a scientific process that has been successfully tested. What is the theory of plate tectonics good for? The motion of Earth's plates help scientists to understand why earthquakes, volcanoes, and mountain building occur. Scientists believe these plates have been moving for millions of years. Their research indicates that 250 millions years ago, the Earth's continents were all grouped together into one super-continent called Pangaea. About 200 million years ago, Pangaea covered approximate ly 30% of Earth’s surface. A large ocean, Panthalassa, covered the rest of the planet. Pangaea Some clues leading scientists to accept the idea of Pangaea were: • Fossil clues • Rock Clues • Climate Clues • Fossil clues: Fossils of the reptile Mesosaurus have been found in South America and Africa. Since the reptile couldn’t swim that distance, Wegener hypothesized that this reptile lived on both continents when they were joined. Additionally, plant fossils and matching rock layers have been found on both continents. • Rock Clues: Similar rocks were found in United States, Western Europe, and Greenland. • Climate Clues: Glacial deposits found in South America, Africa, India and Australia provide additional evidence that continents were connected. Structure of the Earth The Earth is made up of 3 main layers: • Crust • Mantle • Core Crust Mantle Outer core Inner core The Crust This is where we live! The Earth’s crust is made of: 1. Continental Crust - thick - buoyant / kind of floats -(less dense than oceanic crust) - mostly old 2. Oceanic Crust - thin - dense - (sinks under continental crust) - young Let’s model the Earth’s layers What are the layers of the Earth? How are the peach layers similar to Earth’s layers? What are the limitations of this model? The Earth’s layers The crust, mantle and core are labels for describing the three different kinds of materials the Earth is made of. The lithosphere, asthenosphere, mesosphere, outer core & inner core distinguish between the 5 physical layers of the Earth. Lick All My Orange Ice Cream Question: Describe the difference between the crustmantle- core AND LAMOIC How do we know what the Earth is made of? Geophysical surveys: Mostly seismic wave experiments, fieldwork, boreholes, mines What is Plate Tectonics? If you look at a map of the world, you may notice that some of the continents could fit together like pieces of a puzzle. Question Describe plate tectonics in your own words Why are there tectonic plate interactions? Earth is a warm planet sailing through cold space. Most of the mantle of our planet is hot enough to flow. The surface of Earth, however, is chilled as it loses heat into space. As a result, the rocks of Earth’s surface are hard and brittle. The cold outer layer of our planet, which holds together as a rigid shell, is not made of one solid piece. Instead, this shell is broken into separate pieces, or tectonic plates (lithosphere), that slide on top of the mobile interior (asthenosphere). The tectonic plates are driven by the flowing part of the mantle, it sets them in motion. The movement of the plates causes a complex puzzle of plate collisions around the globe. Plate Tectonics The Earth’s crust is divided into 12 major plates which are moved in various directions. (Plate examples: Eurasian, African, IndoAustrailian, Pacific, North American and South American plates This plate motion causes them to collide, pull apart, or scrape against each other. Each type of interaction causes a characteristic set of Earth structures or “tectonic” features. The word, tectonic, refers to the deformation of the crust as a consequence of plate interaction. What are tectonic plates made of? Plates are made of rigid lithosphere. The lithosphere is made up of the crust and the upper part of the mantle. What lies beneath the tectonic plates? Below the lithosphere (which makes up the tectonic plates) is the asthenosphere. Plate Movement “Plates” of lithosphere are moved around by the underlying hot mantle convection currents Convection Currents Hot magma in the Earth moves toward the surface, cools, then sinks again. Creates convection currents beneath the plates that cause the plates to move. There are three types of plate-plate interactions based upon relative motion: Convergent boundary - where plates collide Divergent boundary - where plates separate Transform boundary - where plates slide past one another What happens at a convergent boundary? What forms around that boundary? Plates converge, which means two plates move toward each other. Usually an oceanic plate converges with a continental plate. Since oceanic plates are more dense than continental plates, ocean plates are subducted or go down into the mantle in an area called the subduction zone. Convergent boundaries make subduction zones A convergent boundary can also create a deep-sea trench. At the subduction zone, the temperature of the rocks rises and causes them to melt, which forms magma that is forced upwards to create volcanoes. FYI Convergent Boundaries There are three styles of convergent plate boundaries • Continent-continent collision • Continent-oceanic crust collision • Ocean-ocean collision Continent-Continent Collision Forms mountains, e.g. European Alps, Himalayas Himalayas Convergent boundaries making mountains When two continental plates collide (same densities) and push up the crust, they form mountain ranges such as the Himalayas. This is an example of uplift. No volcanoes form. There is little or no subduction to produce the high temperature required for melting the rocks. Continent-Oceanic Crust Collision Called SUBDUCTION Subduction Oceanic lithosphere subducts underneath the continental lithosphere Oceanic lithosphere heats and dehydrates as it subsides The melt rises forming volcanism E.g. The Andes Ocean-Ocean Plate Collision When two oceanic plates collide, one runs over the other which causes it to sink into the mantle forming a subduction zone. The subducting plate is bent downward to form a very deep depression in the ocean floor called a trench. The worlds deepest parts of the ocean are found along trenches. • Ex. The Mariana Trench is 11 km deep! Divergent boundary Plates separate, which means two plates move away from each other. Usually an oceanic plate diverges from another oceanic plate. Seafloor spreading occurs at divergent oceanic plate boundaries and leads to the creation of new ocean floor. What happens at a divergent boundary? What forms along that boundary? As two tectonic plates slowly separate, molten material rises from within the mantle to fill the opening. As the ocean floor slowly separates, new rocks form at the mid-ocean ridge that is forming. The Mid-Atlantic Ridge is getting wider at a rate of 2.5 cm every year. Mid-ocean ridges Mid-ocean ridges are underwater mountain chains. Although named “mid-ocean”, there are not necessarily at the center of the ocean. Divergent Boundaries Spreading ridges • As plates move apart new material is erupted to fill the gap Sea floor spreading When the sea floor moves, magma moves upward and flows from cracks at the mid ocean ridge. The magma cools and forms a new sea floor. This sea floor spreading idea is supported by the following observations: 1. When scientists tested rocks at the mid-ocean ridge and on both sides of the ridge, they found that the youngest rocks were closer to the ridge and older rocks were farther away from the ridge. 2. Earth has a magnetic field that from time to time reverses magnetic north and south poles. Volcanic rock provides a record of the magnetic poles at the time the rock cooled, thus past reversals are recorded in rocks forming along mid-ocean ridges. Iceland: An example of continental rifting Iceland has a divergent plate boundary running through its middle Transform Boundaries Where plates slide past each other Above: View of the San Andreas transform fault What happens at the transform boundary? What forms along that boundary? Plates slide past each other, and faults or breaks in the Earth’s crust can form there from stress. Stress- the amount of force put on a rock When one plate suddenly slips past another plate and releases the stress, earthquakes occur. The San Andreas fault is part of a transform boundary where the Pacific plate slides against the North American plate. Volcanoes and Plate Tectonics… …what’s the connection? Pacific Ring of Fire Hotspot volcano chain- Hawaiian Islands Volcanos are mostly focused at plate boundaries Pacific Ring of Fire Most of the active volcanoes and earthquakes are located at the plate boundaries. The Pacific Ring of Fire is an area of almost constant earthquake and volcanic activity. It circles the Pacific Ocean basin. Volcanoes are formed by: - Subduction - Rifting - Hotspots What are Hotspot Volcanoes? Hot mantle plumes breaching the surface in the middle of a tectonic plate The Hawaiian island chain are examples of hotspot volcanoes. Photo: Tom Pfeiffer / www.volcanodiscovery.com The tectonic plate moves over a fixed hotspot forming a chain of volcanoes. The volcanoes get younger from one end to the other. Earthquakes and Plate Tectonics… …what’s the connection? As with volcanoes, earthquakes are not randomly distributed over the globe Figure showing the distribution of earthquakes around the globe At the boundaries between plates, friction causes plates to stick together. When built up energy causes them to “unstick”, earthquakes occur. Where do earthquakes form? Figure showing the tectonic setting of earthquakes Plate Tectonics Summary The Earth is made up of 3 main layers (core, mantle, crust) & 5 physical layers (LAMOIC) On the surface of the Earth are tectonic plates that slowly move around the globe Plates are made of crust and upper mantle (lithosphere) and move on the asthenosphere There are 2 types of plates: oceanic and continental There are 3 types of plate boundaries: convergent, divergent & transform Volcanoes and Earthquakes are closely linked to the borders of the tectonic plates Convergent Divergent Transform C-C form mountains using uplift Ex. Alps, Himalayas O-O form mid-ocean ridges (underwater mountain chains) with sea floor spreading All will create fault lines that build up pressure to release earthquakes Ex. San Andes fault CA O-O form subduction zones trenches Ex. Mariana Trench C-C breaks continental crust apart and exposes magma on Earth’s surface Ex. Iceland C-O form volcanoes from subduction zones Ex. Andes Mts. Age of Oceanic Crust Courtesy of www.ngdc.noaa.gov Questions... What is the theory of plate tectonics? What is the lithosphere? What is the asthenosphere? What is the connection between the two? What are the two types of plates? Questions... What are the three types of boundaries? What direction do plates go for each? Which boundary has a subduction zone…what occurs at a subduction zone? Questions... What causes plates to move? How is a convection current formed?