Active volcanoes are most abundant along the

• edges of tectonic plates

• eastern coastline of continents

• 23.5° N and 23.5° S parallels of latitude

• equatorial ocean floor

The edges of most lithospheric plates are characterized by

• reversed magnetic orientation

• unusually rapid radioactive decay

• frequent volcanic activity

• low P-wave and high S-wave velocity

The movement of tectonic plates is inferred by many scientists to be driven by

• tidal motions in the hydrosphere

• density differences in the troposphere

• convection currents in the asthenosphere

• solidification in the lithosphere

Which coastal area is most likely to experience a severe earthquake?

• east coast of North America

• east coast of Australia

• west coast of Africa

• west coast of South America

Which observation about the Mid-Atlantic Ridge region provides the best evidence that the seafloor has been spreading for millions of years?

• The bedrock of the ridge and nearby seafloor is igneous rock.

• The ridge is the location of irregular volcanic eruptions.

• Several faults cut across the ridge and nearby seafloor.

• Seafloor bedrock is younger near the ridge and older farther away.

Which statement best supports the theory of continental drift?

• Basaltic rock is found to be progressively younger at increasing distances from a mid-ocean ridge.

• Marine fossils are often found in deep-well drill cores.

• The present continents appear to fit together as pieces of a larger landmass.

• Areas of shallow-water seas tend to accumulate sediment, which gradually sinks.

Which characteristic of the ocean-floor bedrock is best described by the plus and minus symbols in the diagram?

• 0. plus = older age; minus = younger age
     

• 0. plus = younger age; minus = older age
     

• 0. plus = reversed magnetic polarity; minus = normal magnetic polarity
     

• 0. plus = normal magnetic polarity; minus = reversed magnetic polarity

Which evidence supports the theory of ocean floor spreading?

• The rocks of the ocean floor and the continents have similar origins.

• In the ocean floor, rocks near the mid-ocean ridge are cooler than rocks near the continents.

• The pattern of magnetic orientation of rocks is similar on both sides of the mid-ocean ridge.

• The density of oceanic crust is greater than the density of continental crust.