Transcript Slideshow
Continental Drift &Plate Tectonics Whitney Isbell for use with my 8th Grade Science Class http://www.middleschoolscience.com 2013 Earth’s Layers The Earth's solid rocky outer crust formed billions of years ago, soon after the Earth formed. This crust is not a solid shell; it is broken up into huge, thick plates that drift atop the soft, underlying mantle. The Crust • Lithosphere is made up of the crust and the upper mantle. The lithosphere makes up the plates that move on top of the Asthenosphere. The Mantle • Layer of Earth between the crust and the core • Contains most of the Earth’s mass • A think liquid like silly putty • Molten rock The Core • Below the mantle and to the center of the Earth • Outer Core is molten metal • Inner Core is solid metal Continental Drift Alfred Wegener 1900’s continents were once a single land mass that drifted apart. Fossils of the same plants and animals are found on different continents Shape of the continents fit together like puzzle pieces Rocks are found in different continents that are the same composition Called this supercontinent Pangea, Greek for “all Earth” 245 Million years ago Could not explain why the plates moved http://members.enchantedlearning.com/subjects/astronomy/planets/earth/Continents.shtml Evidence of Pangea Tectonic Plates In the 1960’s scientists discovered seafloor spreading and convection of the mantle caused the plates to move. This was the beginning of the theory of plate tectonics Convection: Heat rises and cool things sink due to density. Magma (molten rock) that is close to the outer core is hotter and begins to rise. As the magma (molten rock) gets closer to the crust it begins to lose heat and sink back down towards the core. This creates convections currents which cause the plates to move. Plate Tectonics • • • • • Greek – “tektonikos” of a builder Pieces of the lithosphere that move around Each plate has a name Fit together like jigsaw puzzles Float on top of mantle similar to ice cubes in a bowl of water Sea Floor Spreading Sea Floor Spreading • Mid Ocean Ridges – underwater mountain chains; largest is the Mid-Atlantic Ridge where the Atlantic ocean is pulling apart and new land is being formed. • Magma rises to the surface and solidifies and new crust forms • Older Crust is pushed farther away from the ridge How Plates Move Convection Currents http://pubs.usgs.gov/gip/dynamic/unanswered.html Different Types of Boundaries http://pubs.usgs.gov/gip/dynamic/understanding.html Divergent Boundary – Arabian and African Plates Divergent Boundary – Iceland http://pubs.usgs.gov/gip/dynamic/understanding.html Divergent Boundary – Oceanic Mid Ocean Ridges http://www.geology.com You can see the Mid-Atlantic Ridge from space Magma rises to the surface when plates are pulling apart and form new land Divergent Boundary – Continental Rift Valleys (Great African Rift Valley) http://www.geology.com New Land was formed in Africa when two plates were pulling apart Convergent Boundary – Indian and Eurasian Plates Convergent Boundary – Oceanic & Continental Oceanic Plates are denser and will subduct (sink) under continental plates. The sinking oceanic plate will form new magma. http://pubs.usgs.gov/gip/dynamic/understanding.html & http://www.geology.com Convergent Boundary – Oceanic & Oceanic Because plates are not the same size the larger oceanic plate will subduct under the less dense oceanic plate and form new magma. http://pubs.usgs.gov/gip/dynamic/understanding.html & http://www.geology.com Convergent Boundaries - Continental Two continental plates will buckle against each other and from folded mountains. http://pubs.usgs.gov/gip/dynamic/understanding.html & http://www.geology.com Transform Boundary – San Andreas Fault www.geology.com Two plates that are sliding past each other will create earthquakes and faults. • Fundamental Questions • What was the early theory of continental drift; who developed it, and when was it developed? • What were the discoveries that led to a theory of plate tectonics, and when were these discoveries made? • What is Earth's lithosphere made of, and how does it affect crustal features? • What features of the Earth's crust do convergent, divergent, and transform boundaries form? • What land features formed by the movement of tectonic plates can be observed using images from space?