Topic/ Lesson for sea floor spreading and the explanation

PowerPoint to understand sea floor spreading

1. LET US CHECK!

2. LET US CHECK!

3. 1. True 2. True 3. False- YOUNGER NEAR THE MOR 4. True 5. True 6. False - THINNER 7. True 8. True 9. False -SEAFLOOR SPREADING 10. False - SUBDUCTION IS FASTER Key Answer 1. C 2. B 3. A 4. B 5. B 6. D 7. C 8. A 9. A 10. C

4. What is SEAFLOOR? the solid surface underlying a  sea  or an ocean. Also  called  seabed .

5. What is SEAFLOOR SPREADING? Seafloor spreading  is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge .

6. What is Mid-ocean Ridge? is an underwater mountain system formed by plate tectonics. It consists of various mountains linked in chains, typically having a valley known as a rift running along its spine .

7. The famous Mid-Atlantic Ridge -undersea chain in the Atlantic ocean -has a gigantic cleft about 32-48 km long and 1.6 km deep

8. What is Seafloor Spreading Theory? -states that hot, less dense material from below the earth’s crust (magma) rises towards the surface at the mid-ocean ridge. This material flows sideways carrying the seafloor away from ridge, and creates a crack in the crust. The magma flows out of the crack, cools down and becomes the new seafloor.

9. Who introduced Seafloor Spreading Theory? Harry Hammond Hess was a geologist and United States Navy officer in World War II. Considered one of the "founding fathers" of the unifying theory of plate tectonics, Rear Admiral Harry Hammond Hess was born on May 24, 1906 in New York City . Harry Hess

10. Robert Sinclair Dietz was a scientist with the US Coast and Geodetic Survey. Dietz was a marine geologist, geophysicist and oceanographer who conducted pioneering research along with Harry Hammond Hess ...  Born :  September 14, 1914 Died :  May 19, 1995,  Tempe, Arizona, United States

11. Sea Floor Spreading During World War II, geologist Harry Hess became interested in mapping the ocean floor using sonar .

12. Sonar - a device that bounces sound waves off under-water objects and then records the echoes of these sound waves. The time it takes for the echo to arrive indicates the distance to the object.

13. Unexpected Finding: Long mountain ranges existed throughout the floors of the oceans called mid-ocean ridges . The longest one runs through the middle of the Atlantic Ocean and is called the Mid Atlantic Ridge (MAR).

14. The force responsible for driving or moving the plates is Convection Current. Convection Currents occur within the mantle of the earth when hot magma rises and cool magma sinks.

15. Magma, because it is hotter and less dense, is forced up towards the ocean floor cooling off when it touches water. When the magma hardens, a small amount of new ocean floor is added to the Earth’s crust. As more magma rises and cools it pushes the new sea floor away from the ridge. This process is called sea floor spreading .

16. Why is it necessary to know about the Seafloor Spreading? To give further explanations about how continents are drifted. To support the Continental D rift T heory (but not totally)

17. Facts and Trivia Findings that support Seafloor Spreading Theory Rocks are YOUNGER at the mid-ocean ridge. Rocks far from the mid-ocean ridge are older. Sediments are thinner at the ridge Rocks at the ocean floor are younger than those at the continents.

18. PROOF THAT THE SEA FLOOR IS SPREADING The oldest ocean floor rocks ever found are 180 million years old. Remember the Earth is 4.6 billion years old. This proves that ocean floor is being destroyed therefore all ocean floor rocks are young compared to the age of Earth . The rocks closest to the ocean ridge were younger than the rocks found further from the ridge. This means that new rocks are formed at the ridges and push the older rocks away from the ridge .

19. 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.

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

21. Sea floor increases in age and is more deeply buried by sediment away from the ridge because sediments have had a longer time to collect. Rates of sea-floor spreading vary from 1 to 10 cm per year for each side of the ridge and can be determined by dating magnetic anomaly stripes of the sea floor and measuring their distance from the ridge crest. Continents are moved by the expanding sea floor.

22. Oceanic crust is much younger than most continental crust. Oceanic lithosphere must have been generated (at ridges) and destroyed (at subduction zones) many times since the formation of the earth. Ocean basins form by stretching and splitting (rifting) of continental crust, and the rise of mantle material into the crack to form new oceanic lithosphere.

23. Among the major ocean basins, the A tlantic has the simplest pattern of ocean-floor ages, which shows that it has opened fairly steadily since its birth . Subduction is confined to relatively small island arc systems in the Caribbean and the extreme south-west.

24. The process of seafloor spreading allowed the creation of new bodies of water. Example: the Red Sea as created as the African plate and the Arabian plate moved away from each other. SFS is also pulling the continents of Australia, South America and Antarctica away from each other in the East Pacific Rise. East Pacific Rise- is one of the most active sites of seafloor spreading with more than 14 cm every year.

25. In the place where two oceanic plates collide or where an oceanic and continental plates collide, a subduction zone occurs. As the new seafloor is formed at the mid-ocean ridge, the old seafloor farthest from the ridge is destroyed at the subduction zone. The rate of formation of a new seafloor is not always as fast as the destruction of the old seafloor at the subduction zone. This explains why the Pacific ocean is getting wider. If subduction is faster than seafloor spreading, the ocean shrinks . When the seafloor spreading is greater than the subduction , then the ocean gets wider.

26. Seafloor Spreading Theory contradicts a part of the Continental Drift Theory because according to C.D.T., continents moved through unmoving oceans and that larger, sturdier continents broke through the oceanic crust but according seafloor spreading shows that the ocean is the actual site of tectonic activity

27. EVALUATION

28. Directions: Study the following diagram of the seafloor. Then match the letters to the statements below. 7. Molten rock flows onto the seafloor and hardens as it cools. 8. Hot, molten rock is forced upward toward the seafloor at a mid-ocean ridge. 9. New seafloor moves away from the ridge, cools, becomes denser, and sinks. 10. Molten rock pushes sideways in both directions as it rises, moving the
mantle with it.