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Inside Earth Continental Drift Sea Floor Spreading Plate Tectonics

Explore the layers of the Earth and the forces that shape our planet's surface. Learn about continental drift, sea floor spreading, and plate tectonics.

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Inside Earth Continental Drift Sea Floor Spreading Plate Tectonics

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  1. Inside EarthContinental DriftSea Floor SpreadingPlate Tectonics

  2. The Earth’s Layers • The Earth is made of many different and distinct layers. The deeper layers are composed of heavier materials; they are hotter, denser and under much greater pressure than the outer layers. • Natural forces interact with and affect the earth’s crust, creating the landforms, or natural features, found on the surface of the earth.

  3. Before we start to look at the forces that contribute to landforms,lets look at the different layers of the earth that play a vital role in the formation of our continents, mountains, volcanoes, etc.

  4. Crust Mantle Outer Core Inner Core

  5. Crust • crust - the rigid, rocky outer surface of the Earth, • The crust is composed of two rocks. The continental crust is mostly granite. The oceanic crust is basalt. Basalt is much denser than the granite. Because of this the less dense continents ride on the denser oceanic plates.

  6. The Crust • The Earth's Crust is like the skin of an apple. It is very thin in comparison to the other three layers. The crust is only about 3-5 miles (8 kilometers) thick under the oceans (oceanic crust) and about 25 miles (32 kilometers) thick under the continents (continental crust).

  7. The crust of the Earth is broken into many pieces called plates. The plates "float" on the soft, semi-rigid asthenosphere. The Lithospheric Plates

  8. The Lithosphere The crust and the upper layer of the mantle together make up a zone of rigid, brittle rock called the Lithosphere.

  9. The Mantle • The Mantle is the largest layer of the Earth. • The middle mantle is composed of very hot dense rock that flows like asphalt under a heavy weight. The movement of the middle mantle (asthenosphere) is the reason that the crustal plates of the Earth move.

  10. The Mantle Composition • mantle - a rocky layer located under the crust - it is composed of silicon, oxygen, magnesium, iron, aluminum, and calcium.

  11. The middle mantle "flows" because of convection currents. Convection currents are caused by the very hot material at the deepest part of the mantle rising, then cooling and sinking again --repeating this cycle over and over. Convection Currents

  12. The core of the Earth is like a ball of very hot metals. The outer core is so hot that the metals in it are all in the liquid state. The outer core is composed of the melted metals of nickel and iron. The Outer Core

  13. The inner core of the Earth has temperatures and pressures so great that the metals are squeezed together and are not able to move about like a liquid, but are forced to vibrate in place like a solid. The Inner Core

  14. DID YOU KNOW?

  15. Land and Water • Photographs of the earth taken from space show clearly that it is truly a ”watery planet.” • More than 70 percent of the earth’s surface is covered by water, mainly the salt water of oceans and seas.

  16. Continental Drift and Seafloor Spreading

  17. Continental Drift Theory • In the early 1900s a German explorer and scientist (Alfred Wegener) proposed the continental drift theory. • He proposed that there was once a single “super continent” called Pangaea. • He believed that the continent floated on the oceanic crust (like an iceberg in the ocean). • Most scientist rejected his theory due to lack of evidence.

  18. Evidence of continental drift • Continents fit together like a jigsaw puzzle • Fossils match across oceans • Rock types and mountain ranges match across oceans • Climate Evidence (Glacial Deposits)

  19. “Puzzle Pieces” • Continents look like they could be part of a giant jigsaw puzzle

  20. Distribution of Fossils • Plant and animal fossils found on the coastlines of different continents

  21. Sequence of Rocks • Same rock patterns found in South America, India, Africa, Antarctica and Australia

  22. Climate • Tropical plant remains (coal deposits) found in Antarctica • Glacial deposits in Africa, South America, India, and Australia during the same time

  23. Sea-Floor Spreading

  24. Ocean floor moves like a conveyor belt carrying continents with it. • New ocean floor forms along cracks in the ocean crust as molten material erupts from the mantle spreading out and pushing older rocks to the sides of the crack. New ocean floor is continually added by the process of sea-floor spreading.

  25. EVIDENCE OF SEA-FLOOR SPREADING……

  26. Sea-Floor Spreading 1. Evidence from Molten Material – Rocks shaped like pillows (rock pillows) show that molten material has erupted again and again from cracks along the mid-ocean ridge and cooled quickly

  27. The mid-ocean ridge system is the most extensive chain of mountains on earth, but more than 90% of this mountain range lies in the deep ocean. The mid-ocean ridge wraps around the globe for more than 65,000 km like the seam of a baseball. Mid-Ocean Ridge

  28. Mid-Ocean Ridge • Mid-ocean ridges occur along the kind of plate boundary where new ocean floor is created as the plates spread apart. "divergent plate boundary." The plates spread apart at rates of 1 cm to 20 cm per year. As oceanic plates move apart, rock melts and wells up from tens of kilometers deep. Some of the molten rock ascends all the way up to the seafloor, producing enormous volcanic eruptions of basalt, and building the longest chain of volcanoes in the world!

  29. Sea-Floor Spreading 2. Evidence from Magnetic Stripes – Rocks that make up the ocean floor lie in a pattern of magnetized stripes which hold a record of the reversals in Earth’s magnetic field

  30. Sea-Floor Spreading

  31. Sea-Floor Spreading 3. Evidence from Drilling Samples – Core samples from the ocean floor show that older rocks are found farther from the ridge; youngest rocks are in the center of the ridge

  32. Sea-Floor Spreading Sea-Floor Spreading – Harry Hess in the 1960’s; the process that continually adds new material to the ocean floor while pushing older rocks away from the ridge

  33. Plate Tectonics

  34. Most of these changes in the earth’s surface takes place so slowly that they are not immediately noticeable to the human eye. • The idea that the earth’s landmasses have broken apart, rejoined, and moved to other parts of the globe forms part of the • plate tectonic theory.

  35. Plate Tectonic Theory Along the mid-ocean ridge the seafloor is pulling apart and the two parts are moving in opposite directions, carrying along the continents and oceans that rest on top of them. These pieces of Earth’s top layer are called tectonic plates. They are moving very slowly, but constantly. (Most plates are moving about as fast as your fingernails are growing -- not very fast!) Currently Earth’s surface layers are divided into nine very large plates and several smaller ones.

  36. According to the theory of plate tectonics, the earth’s outer shell is not one solid piece of rock. Instead the earth’s crust is broken into a number of moving plates. The plates vary in size and thickness.

  37. These plates are not anchored in place but slide over a hot and bendable layer of the mantle.

  38. As mentioned earlier, those tectonic plates are always moving. pulling away from each other (Divergent) crashing head-on (Convergent) or sliding past each other. (Transform)

  39. Divergent Boundaries • Boundary between two plates that are moving apart or rifting   • RIFTING causesSEAFLOOR SPREADING

  40. They’re Pulling Apart! • When plates pull away from one another they form a diverging plate boundary, or spreading zone. Thingvellir, the spreading zone in Iceland between the North American (left side) and Eurasian (right side) tectonic plates. January 2003.

  41. Features of Divergent Boundaries • Mid-ocean ridges • rift valleys • fissure volcanoes

  42. Convergent Boundaries • Boundaries between two plates that are colliding   • There are 3 types…

  43. Ocean to Continent • Ocean plate colliding with a less dense continental plate • Subduction Zone: where the more dense plate slides under the less dense plate • VOLCANOES occur at subduction zones

  44. Continental/Oceanic Crush Subduction – Process by which the ocean floor sinks beneath a deep-ocean trench and back into the mantle; allows part of the ocean floor to sink back into the mantle

  45. Subduction zone Deep-Ocean Trench – Occurs at subduction zones. Deep underwater canyons form where oceanic crust bends downward

  46. Subduction Zone

  47. Andes Mountains, South America

  48. Ocean to Ocean • Ocean plate colliding with another ocean plate • The more dense plate slides under the less dense plate creating a subduction zone called a TRENCH

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