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Earth ’ s Interior, Continental Drift & Plate Tectonics. Earth ’ s Interior (outside to inside). Crust Oceanic – Crust below the oceans Continental – Crust that is made of land Mantle Hot solid layer (piable rock) Asthenosphere (Mantle) Part of the mantle with Convection Currents
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Earth’s Interior (outside to inside) • Crust • Oceanic – Crust below the oceans • Continental – Crust that is made of land • Mantle • Hot solid layer (piable rock) • Asthenosphere (Mantle) • Part of the mantle with Convection Currents • Outer core • Liquid layer – made up of iron and nickel • Inner Core • Solid layer – made up of iron and nickel
An Idea Before Its Time: Continental Drift Wegener’s continental drift hypothesis stated that the continents had once been joined to form a single supercontinent. • Wegener proposed that the supercontinent, Pangaea, began to break apart 200 million years ago and form the present landmasses.
Evidence • Puzzle: Continents can fit together like a puzzle • Fossils: Similar fossils were found on coastlines of different continents.
Evidence Matching Mountains: Mountains that appear on one coastline also appear on another continent across the ocean. Ancient Climates: evidence of glaciers in locations on continents that indicate they were once nearer to the poles.
Missing Evidence A New idea emerges • • Wegener could not provide an explanation of exactly what made the continents move. • New technology leads to findings which then lead to a new theory called plate tectonics.
Plate Tectonics • Theory of Plate Tectonics – Earth’s crust is broken up into sections/pieces that move on top of the pliable mantle (asthenosphere). • Tectonic Plates – these rigid, hard sections/pieces of crust are called plates
Plates • There are 7 major plates on the earth that are moving extremely slowly but continuously. Major Plates: Eurasian, African, Australian-Indian, North American, Pacific, Antarctic and South American. Intermediate Plates: Caribbean, Cocos, Nazca, Arabian, Phillippine, Juan de Fuca and Scotia • 2 main types of plates: • Oceanic - ocean • Continental - land Oceanic Continental
Convection Currents • Convection cells in the mantle move the plates. • Hot in the center, heated, less dense rock in the mantle slowly rises up due to heat. • When the hot rock reaches the athensosphere, it cools and sinks back down creating a circular pattern of movement. • This process happens continually, but very, very slowly • Hot – goes UP • Cool – goes DOWN Cool
Crust Density also plays a role • Oceanic Plates (dense) – heavy • Sink (subduct) underneath continental crust • Continental Plates (less dense) – lighter
Slab-pull and Ridge-Push • Slab-pull – when subducting dense oceanic crust sinks into the mantle and “pulls” the trailing lithosphere along. It is thought to be the strongest mover of plates. • Ridge-push or gravitational sliding causes oceanic lithosphere to slide down the steep sides of the mid oceanic ridge under the pull of gravity. It may contribute to plate motion.
Evidence for Plate Motion So plates can collide, separate and slide paste each other. But how do we know?
Evidence for Plate Tectonics Paleomagnetism: iron based minerals in igneous rock can have natural magnetism that matches the magnetic field of the earth at the time it was formed. (observed in lava flows) • Normal polarity—when rocks show the same magnetism as the present magnetism field • Reverse polarity—when rocks show the opposite magnetism as the present magnetism field
EvidenceforPlateTectonics The discovery of strips of alternating polarity, which lie as mirror images across the ocean ridges, is among the strongest evidence of seafloor spreading.
Evidence for Plate Tectonics Ocean Drilling • The data on the ages of seafloor sediment confirmed what the seafloor spreading hypothesis predicted. • The youngest oceanic crust is at the ridge crest, and the oldest oceanic crust is at the continental margins.
Evidence for Plate Tectonics Hot Spots • Hot spot evidence supports that the plates move over the Earth’s surface. • A hot spot is a concentration of heat in the mantle capable of producing magma, which rises to Earth’s surface often forming volcanoes. As a plate moves over the hot spot, a trail of volcanoes is formed. The Pacific plate moves over a hot spot, producing the Hawaiian Islands.
Plate Boundaries • Border between 2 plates • 3 Boundary Types • Divergent • Convergent • Transform
Divergent Boundaries • Plates moving apart.
Mid-Ocean Ridges(oceanic-oceanic) A mountain under the ocean A mid-ocean ridge forms where oceanic plates continue to separate.
Seafloor Spreading • The process by which new oceanic crust is created at mid ocean ridges. • As oceanic plates move apart, magma comes up. As rising magma cools, it forms new oceanic crust. (Example: Mid-Atlantic Ridge)
A Rift Valley(continental-continental) • When continental plates pull apart, they form rift valleys. • Makes volcanoes and new land (Example: East African Rift Valley)
Convergent Boundaries • Plates come together
Subduction Zones dense When one plate goes under another plate. The more dense (heavier) plate goes under.
Volcanic Arc(Subduction: Oceanic-Continental) • More dense (heavier) oceanic crust goes under the less dense continental crust. • As the plate moves under the continental plate, the rock melts and rises, creating volcanoes.
Deep-Sea Trench(oceanic-continental) A depression or trench in the ocean floor at a subduction zone between oceanic and continental plates
Volcanic Island Chains(Subduction: Oceanic-Oceanic) • When 2 oceanic plates meet and one goes under the other. • Forms Volcanic Islands. (Example: Aleutian Islands)
Mountains(Subduction: Continental-Continental) • When 2 continental plates come together. • The plates push up and form mountains. (Example: Himalayas)
Transform Fault Boundaries • Plates slide past one another moving in opposite directions. • Also called FAULTS • Causes earthquakes/tsunamis to occur. • Very common around mid-ocean ridges.
