seafloor-spreading-answers

A) African Plate and the Eurasian Plate B) Pacific Plate and the Philippine Plate C) Indian-Australian Plate and the Antarctic Plate D) South American Plate and the North American Plate 1. Crustal formation, which may cause the widening of an ocean, is most likely occurring at the boundary between the A) convergent plate boundary between the Pacific Plate and the North American Plate B) convergent plate boundary between the Pacific Plate and the Juan de Fuca Plate C) divergent plate boundary between the Pacific Plate and the North American Plate D) divergent plate boundary between the Pacific Plate and the Juan de Fuca Plate 2. Oceanic crust is sliding beneath the Aleutian Islands in the North Pacific Ocean, forming the Aleutian Trench at a 3. Base your answer to the following question on the map below, which shows crustal plate boundaries located along the Pacific coastline of the United States. The arrows show the general directions in which some of the plates appear to be moving slowly. A) The bedrock is youngest at the ridge. B) The bedrock is oldest at the ridge. C) The bedrock at the ridge is the same age as the bedrock next to the continent. D) The bedrock at the ridge is the same age as the bedrock at the San Andreas fault. What would a study of the East Pacific rise (a mid-ocean ridge) indicate about the age of the basaltic bedrock in this area?

Base your answers to questions 4 through 8 on the diagram below which shows the magnetic orientation of igneous rock on the seafloor on the east (right) side of a mid-ocean ridge. The pattern on the west (left) side of the ridge has been omitted. The age of the igneous rock and its distance from the ridge center are shown. A) B) C) D) 4. Which diagram below best represents the pattern of magnetic orientation in the seafloor on the west (left) side of the ocean ridge? A) The orientation of the Earth's magnetic field has reversed with time. B) The size of the continents has changed with time. C) The elevation of sea level has changed with time. D) The amount of fossil material preserved in the igneous rock has changed with time. 5. Which inference can best be made from the diagram? A) decreases B) increases C) remains the same 6. As distance from the center of the ridge increases, the age of the rocks A) 1 km/million years B) 2 km/million years C) 40 km/million years D) 50 km/million years 7. According to the diagram, what is the approximate rate of seafloor spreading? A) destruction of oceanic crust B) destruction of continental crust C) existence of ancestral mountains D) existence of rising mantle convection currents 8. The occurrence of high-heat floors at the ridge center provides evidence of the A) B) C) D) 9. Which cross-sectional diagram of a portion of the crust and mantle best shows the pattern of mantle convection currents that are believed to cause the formation of a mid-ocean ridge?

A) convergence of the Nazca Plate and the South American Plate B) divergence of the African Plate and the South American Plate C) subduction of the Philippine Plate by the China Plate D) transform faulting between the Pacific Plate and the North American Plate 14. The mid-oceanic ridge portion of this cross section best represents Base your answers to questions 15 through 17 on the passage below. Crustal Activity at Mid-Ocean Ridges Mid-ocean ridges are found at one type of tectonic plate boundary. These ridges consist of extensive underwater mountain ranges split by rift valleys. The rift valleys mark places where two crustal plates are pulling apart, widening the ocean basins, and allowing magma from the asthenosphere to move upward. In some cases, mid-ocean ridges have migrated toward nearby mantle hot spots. This explains why mid-ocean ridges and mantle hot spots are found together at several locations. A) Canary Islands B) Easter Island C) Hawaii D) Tasman 15. Which mantle hot spot is located closest to a mid-ocean ridge? A) A B) B C) C D) D 16. The map below shows a part of Earth’s surface. Points A through D are locations on the ocean floor. At which location is the temperature of the ocean floor bedrock most likely highest? A) convergent B) transform C) divergent D) complex 17. Which type of tectonic plate boundary is located at mid-ocean ridges?

Base your answers to questions 18 and 19 on the map below which shows mid-ocean ridges and trenches in the Pacific Ocean. Specific areas A , B , C , and D are indicated by shaded rectangles. A) shale B) limestone C) granite D) basalt 18. The crust at the mid-ocean ridges is composed mainly of A) mountains containing folded sedimentary rocks B) mountains containing fossils of present-day marine life C) sections of the ocean floor that contain the youngest oceanic crust D) sections of the ocean floor that are the remains of a submerged continent 19. Mid-ocean ridges such as the East Pacific Rise and the Oceanic Ridge are best described as

Base your answers to questions 24 through 26 on the map below, which shows the location of mid-ocean ridges and the age of some oceanic bedrock near these ridges. Letters A through D are locations on the surface of the ocean floor. A) A B) B C) C D) D 24. Rising convection currents in the asthenosphere would most likely be under location A) diverging B) converging C) locked in place D) being subducted 25. The age of oceanic bedrock on either side of a mid-ocean ridge is supporting evidence that at the ridges, tectonic plates are A) 5 B) 12 C) 48 D) 62 26. What is the most probable age, in millions of years, of the bedrock at location B ?

Base your answers to questions 27 and 28 on the map below. The map shows the continents of Africa and South America, the ocean between them, and the ocean ridge and transform faults. Locations A and D are on the continents. Locations B and C are on the ocean floor. A) B) C) D) 27. Which graph best shows the relative age of the ocean-floor bedrock from location B to location C ? A) A B) B C) C D) D 28. The hottest crustal temperature measurements would most likely be found at location

A) B) C) D) 34. The map below shows a portion of Earth's surface. Points X and Y are locations on the lithosphere. Which cross section shows the inferred movement of material in the asthenosphere beneath points X and Y ? A) The bedrock of the ridge and nearby seafloor is igneous rock. B) The ridge is the location of irregular volcanic eruptions. C) Several faults cut across the ridge and nearby seafloor. D) Seafloor bedrock is younger near the ridge and older farther away. 35. Which observation about the Mid-Atlantic Ridge region provides the best evidence that the seafloor has been spreading for millions of years? A) African plate and Antarctic plate B) Nazca plate and South American plate C) China plate and Philippine plate D) Australian plate and Eurasian plate 36. Seafloor spreading is occurring at the boundary between the A) A B) B C) C D) D 37. The diagram below shows the magnetic polarity preserved by minerals within the bedrock of the oceanic crust near the Mid-Atlantic Ridge. Letters A , B , C, and D represent locations in the ocean-floor bedrock. The most recently formed bedrock is found at location

A) Hawaii Hot Spot B) Yellowstone Hot Spot C) Galapagos Hot Spot D) Canary Hot Spot 38. The diagram below shows a tectonic plate boundary. Which mantle hot spot is at a plate boundary like the one shown in this diagram?

A) 1.8 million years ago B) 2.0 million years ago C) 3.0 million years ago D) 4.5 million years ago 41. The scale below shows the age of the sea-floor crust in relation to its distance from the Mid-Atlantic Ridge. Crust that originally formed at the Mid-Atlantic Ridge is now 37 kilometers from the ridge. Approximately how long ago did this crust form? Base your answers to questions 42 and 43 on the map and profile shown below. The map shows the major areas of the North Atlantic Ocean. Letters A , B , C , and D represent locations on the ocean floor. The profile represents the ocean bottom from point X in North America along the dashed line to point Y in Africa. Note that the profile is vertically exaggerated. A) distance from continental landmasses B) topography of the ocean floor C) age of ocean-bottom rocks D) type of ocean-bottom sediments 42. Classification of the ocean bottom into the areas shown is based on the

A) All ocean-floor rocks are generally the same age. B) Rocks at location C are generally older than rocks at locations A and B . C) Rocks at location C are generally younger than rocks at locations A and B . D) Igneous rocks at location D are generally younger than rocks at location C . 43. Which statement about the age of ocean-floor rocks is correct? Base your answers to questions 44 and 45 on the map of the Mid-Atlantic Ridge shown below. Points A through D are locations on the ocean floor. Line XY connects locations in North America and Africa. A) D C B A B) A D B C C) C B D A D) A B D C 44. Samples of ocean-floor bedrock were collected at points A , B , C , and D. Which sequence show the correct order of the age of the bedrock from from oldest to youngest? A) B) C) D) 45. In which cross section do the arrows best show the convection occurring within the asthenosphere beneath line XY ?

Base your answers to questions 48 and 49 on the diagram below which is a cross section of the major surface features of the Earth along the Tropic of Capricorn (23½º S) between 75º W and 15º E longitude. Letters A through G represent locations on the Earth's crust. A) A B) F C) G D) D 48. Which location is closest to the Prime Meridian (0º longitude)? A) A and C B) C and E C) D and F D) E and F 49. Which two locations in the diagram have bedrock of approximately the same age, which has been separated by seafloor spreading?

A) The crystal size of the rock decreases constantly as distance from the mid-ocean ridge increases. B) The temperature of the basaltic rock increases as distance from the mid-ocean ridge increases. C) Heat-flow measurements steadily increase as distance from the mid-ocean ridge increases. D) The age of the igneous rock increases as distance from the mid-ocean ridge increases. 50. The diagram below represents a partial cross section of a model of the Earth. The arrows show inferred motions within the Earth. Which property of the oceanic crust in regions F and G is a result of these inferred motions?

A) Peru-Chile Trench B) Mariana Trench C) Canary Islands Hot Spot D) Iceland Hot Spot 53. Convection currents in the plastic mantle are believed to cause divergence of lithospheric plates at the 54. Base your answer to the following question on the map below which shows the locations of deep-sea core drilling sites numbered 1 through 4. The approximate location of the diverging plate at the East Pacific Ridge is shown by a dashed line. Point A is located on the East Pacific Ridge. A) 1 B) 2 C) 3 D) 4 At which drilling site would the oldest igneous bedrock most likely be found? A) converging and located at an oceanic ridge B) converging and located at an oceanic trench C) diverging and located at an oceanic ridge D) diverging and located at an oceanic trench 55. The border between the South American plate and the African plate is best described as

A) B) C) D) 56. The map below shows the Atlantic Ocean divided into zones A , B , C , and D . The Mid-Atlantic Ridge is located between zones B and C . Which graph best represents the geologic age of the surface bedrock on the ocean bottom? A) A B) B C) C D) D 57. The diagram below represents a cross section of a portion of the Earth's crust and mantle. Letters A , B , C , D and X identify locations within the crust. The age of oceanic crust increases along a line between location X and location A) A B) B C) C D) D 58. The cross section below shows the ocean floor between two continents. Points A through D represent locations on the ocean floor where samples of oceanic crust were collected. The youngest rock sample most likely was collected from location 59. Base your answer to the following question on the diagrams below of geologic cross sections of the upper mantle and crust at four different Earth locations, A , B , C , and D . Movement of the crustal sections (plates) is indicated by arrows, and the locations of frequent earthquakes are indicated by *. Diagrams are not drawn to scale. A) A B) B C) C D) D Which location best represents the boundary between the African plate and the South American plate?