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Dynamic Crust Continental Drift - The Theory Theory that all of the continents were once joined together in a single landmass and have since drifted apart. Pangaea “All Earth” or name given to the super continent that existed 200 million years ago. Alfred Wegener, 1915 • German geologist and meteorologist • Proposed the theory of continental drift • Hypothesized a gigantic super continent Continental Drift - Evidence 1. Similarities in the shape of Africa’s west coast and South America’s east coast. Continental Drift - Evidence 2. Fossil remains of the Mesosaurus were found in South America and South Africa. Continental Drift - Evidence 3. Fossil remains of the Glossopteris were found throughout India, South America, Africa, and Antarctica. Crustal Activity • Plate Tectonics - the study of the formation and movements of plates • Plates - section of the lithosphere that moves around • Lithosphere - Earth’s solid outer crust and rigid mantle • Asthenosphere - partially melted layer that flows slowly and is located below the lithosphere (plastic) Crustal Activity • Earth’s surface consists of a dozen major plates and some minor ones. • The plates are moving at rates close to 10 cm/year • Convection Currents - driving force of plate movement • Magma heats up causing it to expand and rise • Magma cools down causing it to contract and sink • The plates are moving on top of the asthenosphere due to density differences. • The idea of continental drift had been around since the early 1900’s, but lacked enough scientific evidence to support the theory. • New advancements after World War II help provide the evidences needed to validate the Theory of Plate Tectonics. Crustal Activity - Earthquake Evidence • Scientist noticed that earthquakes do not occur at random location, but run throughout the world along isolated belts • When plotted on a map they outline the plate boundaries Crustal Activity – Volcanic Evidence • Occurs at plate boundaries where plates are interacting • Ring of Fire - isolated belt around the Pacific Ocean where 90% of the world’s volcanoes exist Crustal Activity – Rock Evidence • Sedimentary deposits and igneous lava flows are usually placed down in horizontal layers. • Sometimes movement along boundaries causes these layer to tilt or fold Crustal Activity – Mountain Evidence • As plates collide they sometimes are pushed upward. • Fossilized marine organisms can be found at these high altitudes in the rock. Crustal Boundaries • Tectonic plates are constantly moving and interacting • As they move across the asthenosphere and form plate boundaries they interact in various ways • The types of plate boundaries are: • Divergent • Transform • Convergent Crustal Boundaries Crustal Boundaries • Convergent Boundary - boundary where two lithospheric plates are coming together. • Example: the India Plate pushing upward into Eurasian Plate and creating the Himalayan Mountains Crustal Boundaries • Convergent - Subduction while plates are moving together, one plate is pushed below another and consumed in the mantle • Example: the Nazca Plate being consumed under the South American Plate. Crustal Boundaries • Three Types of Convergent Boundaries: • Ocean / Ocean Boundary • Ocean / Continental Boundary • Continental / Continental Boundary Crustal Boundaries • Divergent Boundary - boundary where two plates are moving apart • Example: the Mid Atlantic Ridge Crustal Boundaries • Sea Floor Spreading the process where ocean floor is extended when two plates move apart • Mid Ocean Ridge underwater mountain range created from a divergent plate boundary Crustal Boundaries • Mid Atlantic Ridge a mid ocean ridge that runs the length of the Atlantic Ocean • Separates the North and South American Plates from the Eurasian and African Plates Crustal Boundaries • Rift Valley - long narrow valley that runs the entire length of a mid ocean ridge system Crustal Boundaries • Scientists dragged a magnetometer across the ocean floor and discovered a unique magnetic pattern where stripes of normal and reversed polarity parallel the mid ocean ridge flipping every 200,000 to 300,000 years the last one was781,000 years ago. Crustal Boundaries • Rock samples of the deep ocean floor show that basaltic oceanic crust becomes progressively younger as you approach the mid ocean ridge Crustal Boundaries • Transform Boundary - boundary where two lithospheric plates are sliding past one another • Example: the San Andreas Fault is 800 km long and runs throughout California Earth’s Interior • Earth’s interior structures are known through the study of seismic waves • Seismic waves refract, reflect, change velocity, and are absorbed depending on the material they are transmitted through. Earth’s Interior •Lithosphere - Earth’s crust and outer most layer •Continental Crust - thickest (100 km) and least 3 dense 2.7 g/cm part of the lithosphere •Oceanic Crust - thinnest (2-3 km) and most dense part of the lithosphere 3.0 g/cm3 Earth’s Interior • MOHO - thin interface separating the lithosphere from the asthenosphere • Asthenosphere - a partially melted layer that allows for parts of the lithosphere to move • Discovery: a decrease in velocity from earthquake waves Earth’s Interior • Mantle - thickest part of Earth (80%) and is between the crust and the outer core Earth’s Interior • Outer Core - liquid layer of Earth’s interior between the mantles and the inner core • Discovery: the absorption and refraction of earthquake waves Earth’s Interior • Inner Core - the solid inner most zone of Earth’s core composed of iron (Fe) and nickel (Ni) • Discovery: an increase in velocity from earthquake waves Earthquakes •Earthquake - a natural shaking of the lithosphere caused by a release of energy stored in rocks •Most earthquakes are caused by a movement along a fault where potential energy is given o" as a seismic wave • Epicenter - on Earth’s surface directly above the focus • Focus - point inside the Earth where the earthquake originates Earthquakes • Seismometer - An instrument used to measure and record movements in the ground Earthquakes Seismogram - record of the seismometer Earthquakes • Mercalli Scale - scale that measures the intensity of an earthquake based on the effects to Earth’s surface, humans, objects in nature, and other man made structures. Earthquakes • The values will differ based on the distance from the epicenter: •Highest intensities are closer •Lower intensities are farther away Earthquakes Richter Scale – logarithmic scale that measures the amount of energy released during an earthquake Magnitude - a number to quantify the amount of seismic energy released from an earthquake Earthquakes • The Richter Scale’s magnitude is determined from the following measurement: •Seismogram’s amplitude of waves •Distances from other seismographs •Epicenter distance Earthquakes • Primary Wave (P – wave) •are the fastest waves • Travels through solids, liquids, and gases • Compressional - particles travel in the direction of wave movement Earthquakes •Secondary Wave (S – waves) •are the slower wave • Travels through solids only • Shear particles travel in right angles to the direction of wave movement Earthquakes •Seismic waves radiate away from the focus Earthquakes • Shadow Zone area in which seismic waves are not detected due to the liquid outer core Earthquakes • P - waves are refracted when they reach the liquid outer core • S - waves are absorbed when they reach the outer core and are not transmitted through to the other side Earthquakes • Epicenters are located using the velocity differences between the pwave and swave Earthquakes • Since p-waves travel faster then s-waves, as your distance increases from the earthquake’s epicenter the arrival time between the two waves will be greater Earthquakes Distance to the epicenter is determined by comparing the arrival times and the E.S.R.T. Earthquakes To find the epicenter location you need to triangulate a position using three different seismometer stations. This is called TRIANGULATION.