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PLATE TECTONICS
SEAFLOOR BATHYMETRY
VARIOUS METHODS OF MEASURING OCEAN DEPTH
A. Sounding line โ weighted rope lowered overboard until it touched the ocean bottom; this old method is time-consuming and inaccurate B. Echo sounding โ type of sonar which measures depth by emitting a burst of high frequency sound and listening for the echo from the seafloor. Sound is emitted from a source on the ship and the returning echo is detected by a receiver on the ship. Deeper water means longer time for the echo to return to the receiver. C. Satellite altimetry โ profiles the shape of the sea surface by measuring the travel time of a radar pulse from the satellite to the ocean surface and back to the satellite receiver. The shape of the sea surface approximates the shape of the sea floor. FEATURES OF THE OCEAN FLOOR
A. Continental margin โ submerged outer edge of the continent where continental crust transitions into oceanic crust Passive or Atlantic type โ features a wide, gently sloping continental shelf (50-200m depth), a steeper continental slope (3000-4000m depth), and a flatter continental rise. Active or Pacific type โ characterized by a narrow shelf and slope that descends into a trench or trough B. Abyssal plain is an extremely flat, sedimentcovered stretches of the ocean floor, interrupted by occasional volcanoes, mostly extinct, called seamounts. Abyssal hills are elongate hills, typically 50-300m high and common on the slopes of mid oceanic ridge. These hills have their origins as faulted and tilted blocks of oceanic crust. C. MID-OCEAN RIDGES A submarine mountain chain that winds for more than 65,000 km around the globe. It has a central rift valley and rugged topography on its flanks. Mid-ocean ridges are cut and offset at many places by transform faults. The trace of a transform fault may extend away from either side of the ridge as a fracture zone which is older and seismically inactive. D. DEEP-OCEAN TRENCHES Narrow, elongated depressions on the seafloor many of which are adjacent to arcs of island with active volcanoes; deepest features of the seafloor. E. SEAMOUNTS AND VOLCANIC ISLANDS Submerged volcanoes are called seamounts while those that rise above the ocean surface are called volcanic islands. These features may be isolated or found in clusters or chains. F. CONTINENTAL SHELF, SLOPE, RISE Continental shelf- Partly shallow extension of the continent underwater.
DIFFERENT METHODS OF DETERMINING THE AGE OF A STRATIFIED ROCK
Stratified rocks are layered rocks formed due to the deposition of items such as sand and silt near the riverbeds, forming layers on top of each other. Relative Dating - is the technique used to determine the age by comparing the historical remains to the nearby layers a. Stratigraphy This technique assumes that the lowest layer is the oldest while the topmost layer is the youngest layer. It is one of the oldest methods of relative dating. b. Biostratigraphy The faunal deposits such as fossils of dead animals are used to establish a strategy for dating. It is an extended version of the stratigraphy. c. Cross Dating The fossils of one layer are compared with another layer with known dating. The principle of cross-cutting relationships states that a fault or intrusion is younger than the rocks that it cuts through. The Law of Superposition states that younger strata lie on top of older strata. The Principle of Cross-Cutting Relationships states that intrusions and faults that cut across rock are necessarily younger than that rock. Inclusions, or foreign bodies, found inside the rock are necessarily older than that rock. Absolute Dating is a technique that determines the exact numerical age of a historical remaining. a. Radiometric dating It determines the age of the sample by measuring the amount of a particular radioactive isotope present in the sample. The age can be determined by the rate of decay of that isotope. The type of radioactive isotope used depends on the type of sample. One of the most popular and widely used types of a radioactive isotope in this type of technique is b. Amino acid dating The change in the protein content of a biological sample can be used to determine the age. A particular form of living being may have a defined protein content in their bodies that deteriorates with time.
