More Related Content
More from MaryAnnLazarteBesar (20)
Recently uploaded (20)
Lesson 8 in Earth and Life Science -Seafloor Spreading
- 1. Objectives 1. Explain how seafloor spreads
- 2. Evidences that supports the continental drift theory: ≒ Edges of the continents fit together ≒ Similarity of rock types found in another continents ≒ Matching of fossils
- 3. Wegeners Continental Drift Theory was not easily accepted because he was not able to substantially explain the process on how continents are drifting. Years later another scientist proposed a theory that can prove the drifting of the continents. This was Harry Hess in his work The History of Ocean Basins' in 1962 which tells how the continents are drifting. This theory is now known as the Theory of Seafloor Spreading.
- 4. What is seafloor? Seafloor is the floor of the ocean It is also called the seabed
- 9. In 1960, Harry Hess proposed that seafloor separates at mid-ocean ridges where new crust forms by upwelling magma.
- 10. Newly formed oceanic crust moves laterally away from the ridge with the motion like that of a conveyor belt. Old oceanic crusts are dragged down at the trenches and re-incorporated back into the mantle.
- 11. The process is driven by mantle convection currents rising at the ridges and descending at the trenches.
- 12. Seafloor spreading rates have slowed down by roughly 35% globally, according to a study that analyzed data from the last 19 million years. Growing mountains might be one of the factors driving the slowdown.
- 13. The magma cools to form a new oceanic crust These activities occur along mid-ocean ridges- large mountain ranges rising from the ocean floor.
- 14. Harry Hess was a geologist that was a captain in the Navy during WWII. His ship was equipped with sonar and he was able to study the seafloor. NASA He was able to map portions of the seafloor and his observations led him to propose a new hypothesis known as Seafloor Spreading.
- 15. It was realized that all along the mid-oceanic ridges, volcanic eruptions are common and they bring huge amounts of lava to the surface in this area.
- 16. The rocks equidistant on either side of the crest of mid-oceanic ridges show remarkable similarities in terms of the period of formation, chemical compositions and magnetic properties. Rocks closer to the mid-oceanic ridges are younger
- 17. The age of the rocks increase as one moves away from the crest. The ocean crust rocks are much younger than the continental rocks The age of rocks in the oceanic crust is nowhere more than 200 million years old.
- 18. The seafloor reveals valuable clues about processes such as plate tectonics. We are familiar with the wide diversity of landforms and geologic processes on the continents - but there is an equal diversity in the ocean basins. The oceans contain volcanoes, mountain chains, valleys, plateaus, etc. Evidence from the Seafloor
- 21. Continental shelf The continental shelf is an area of relatively shallow water, usually less than a few hundred feet deep, that surrounds land. It is narrow or nearly non-existent in some places; in others, it extends for hundreds of miles. The waters along the continental shelf are usually productive, both from light and nutrients from upwelling and
- 22. Abyssal plains Abyssal plains are the largest habitat on earth,at depths of over 10,000 feet and covering 70% of the ocean floor
- 23. Seafloor Topography Continental shelf Narrow, shallow ocean surrounding continents Abyssal plain Relatively level seafloor, often with volcanoes Lost City
- 24. Mid-ocean ridge Rising up from the abyssal plain, you would encounter the mid-ocean ridge, an underwater mountain range, over 40,000 miles long, rising to an average depth of 8,000 feet. Tracing their way around the global ocean, this system of underwater volcanoes forms the
- 25. -It is where seafloor spreading occurs
- 26. Ocean trenches -the deepest part of the ocean Marianas Trench is the deepest place in the o cean
- 28. Seafloor Topography Oceanic ridge Submarine mountain range that is a source of volcanic activity. Topographic feature winding through the ocean basins like the seams on a baseball 70,000 km long. Often found toward center of ocean basins Oceanic trench Narrow, deepest portion of ocean floor (Puerto Rico trench) Found adjacent to some continents or island chains and along the margins of oceans Most common around Pacific Ocean Lost City
- 29. Dotting the deep-ocean floor are isolated volcanic peaks called seamounts. They are most common in the Pacific Ocean. They may gradually sink and erode below sea level. Guyots submerged, flat- topped seamounts. Coral atolls are sinking volcanic island flanked by coral reefs. Seafloor Topography
- 30. Oceanic ridges Magma rises from mantle, forms new oceanic crust Expansion of seafloor results in high elevations Seafloor moves away from ridge (conveyer belt) creating a gap for new material USGS
- 31. Oceanic trench Older seafloor descends into mantle Melting of rocks in the mantle forms magma resulting in volcanism Earthquakes are common where old seafloor is subducted. USGS
- 34. Since the advent of the concept of seafloor spreading, the interest in the problem of distribution of oceans and continents was revived.
- 35. It was in 1967, McKenzie, Parker and Morgan, independently collected the available ideas and came out with another concept termed Plate Tectonics.
Editor's Notes
- #26: Harry Hess , a geologist who wound up serving as a naval commander during WWII. It was during this time that he made many of the observations and measurements that would provide the foundation of plate tectonic theory. America was keenly interested in the seafloor because of submarine warfare.
- #47: Other evidence that led Hess and others to propose seafloor spreading was based upon magnetic surveys of the seafloor. Magnetic data showed that the seafloor had different magnetic zones. Some areas were magnetized consistent with the Earths current magnetic field but other areas were anomalous and seemed to have a magnetization that was the opposite of the Earths magnetic field. These magnetic stripes appeared to be parallel to the ridge axis.
- #50: Think of the Earths magnetic field as being a giant bar magnet - today the Earths magnetic north pole is nearly coincident with its geographic (rotational) north pole. What we have found is that the Earths magnetic field has reversed itself many times in the past - the magnetic south pole aligns itself with the geographic north pole.