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1. The Earth’s Interior, Continental Drift and Theory of Plate Tectonics
2. Formation of oceanic crust at rift zones located in the mid-oceanic floors. Upwelling of magma later solidifies beneath the oceans to produce the crust
3. Earth’s Internal structure
5. The Crust – the rigid outer cover of the earth stretching about 5 miles under Oceans and about 40 miles under some mountains
6. Lithosphere – comprises all materials that form the crust and the upper mantle (rocks, soil, etc)
4. Earth’s Internal Structure The Earth is composed of rocks of different densities.
1. Inner Core – made up of solid iron
2. The Outer Core – liquid iron
3. The Mantle - a dense solid material that makes up about 80% of earth's material
4. Astenosphere – upper part of the mantle
5. Theory of Continental Drift The idea that the continents have originated from a single SUPER CONTINENT was first proposed as a scientific hypothesis in 1920-s by Alfred Wegener
He hypothesized that a single super continent (Pangaea - "whole land") existed on Earth about 250 million years ago.
The super continent later broke down into two pieces:
a) a northern half called Eurasia and
b) a southern portion called Gondwanaland.
The Continental Drift Theory did not gain worldwide support because it could not account for the forces that break up and move the continents
6. Continental Drift Theory
8. Theory of Plate Tectonics In the 1960s, the Continental drift theory was replaced by the theory of plate tectonics. The discovery of alternating patterns of rock magnetism in surface rocks and sea-floor spreading aided in the creation of the plate tectonics theory.
Modern plate tectonic theory states that the surface crust of the Earth is composed of many independent segments called plates. These plates have the ability to move horizontally by gliding over the plastic asthenosphere .
9. Continental Plates Plate tectonics theory explains that the Lithosphere consists of as many as 7 huge plates & about 5 smaller plates that move as distinct units.
The plates form the continents, islands, and the floor of the oceans.
10. Convection Currents Modern tectonic theory explains that crustal movements are caused by a very slow thermal convection currents within the earth.
Hot magma is rising from deep inside the earth until it reaches the crust, and crustal blocks are submerging into mantle.
11. Lithosphere moves over the asthenosphere
12. Types of Plate Movements -- 1 Divergence - Plates move away from each other (e.g. mid-Atlantic ridge, East African rift valley)
Lateral Movement as in Transform Plate boundaries where plates slide past one another along strike-slip faults such as the San Andreas Fault in California.
13. Types of Plate Movements --2 Lateral movements: as in Subduction Zones where Oceanic plates slides beneath Continental plates (e.g. the coasts of Peru and Chile, Eastern Philippines and Japan). These are zones of deep ocean trenches.
Lateral plate movements can cause Faulting and the FOLDING of the crust into mountains (e.g. Appalachian & Rockies in US, the Alps of Europe, the Andes mountains of South America and the Himalayas mountains of Asia.
14. Sea Floor Spreading & Plate Boundaries
15. Tectonic features of the world
16. Divergent plate movement At some plate boundaries, plates are moving away from each other because of sea-floor spreading.
An example is the mid-Atlantic Ridge between Africa and North America
17. Collision of an Oceanic plate with a Continental plate
18. Formation of the Himalaya Mountains. Compressional forces due to the collision of the Eurasian and Indian continental plates caused ocean sediments and continental rocks to be pushed upward in elevation. (Source: U.S. Geological Survey). Formation of Himalayas Mountains
19. Collision of two Continental Plates When two continental plates collide, one of the crustal plates is subducted under the other producing a mountain range at the plate boundaries e.g. Himalayas.
Sometimes earthquakes also occur at the plate boundaries.
20. Collision of two Oceanic Plates In this type of a collision, (collision of North America and Pacific Plates (Aleutian Islands) one of the plates is subducted under the other creating a deep oceanic trench
The Marianas trench in the Pacific ocean is created by the collision of the fast-moving Pacific Plate against the slower moving Philippine Plate.
Convergence of two oceanic plates also creates a chain of volcanic islands called Island arcs.
21. Marginal features found at the interface of the continents and the ocean basins Features along continental margins