Post-drift studies and Convectional Current Theory

Correct answer: B. Old oceanic floor

Older floors are cooler and have had more time for sediment accumulation. In exams, connect low heat and thick sediments with old ocean floor.

Correct answer: C. Because iron-bearing minerals can preserve magnetic direction

Iron-bearing minerals in basalt record Earth's magnetic direction during cooling. In exams, treat basalt as a magnetic record.

Correct answer: B. Sea-floor spreading explained active formation of the ocean floor

Wegener emphasized drifting continents, while sea-floor spreading explained ocean-floor creation and movement. In exams, see them as stages of development, not opposites.

Correct answer: A. If they are asymmetrical and unordered on both sides of the ridge

Unordered and asymmetrical stripes would not prove systematic spreading. In exams, consider symmetry and order as the key conditions.

Correct answer: B. Upwelling and partial melting of mantle material

At divergent boundaries, mantle rises and partially melts to form magma. In exams, link ridge volcanism with mantle upwelling.

Correct answer: A. By formation of new crust at the Mid-Atlantic Ridge

Spreading at the Mid-Atlantic Ridge separates plates on both sides. In exams, use the Atlantic as an example of active spreading.

Correct answer: B. Because oceanic plates subduct there

Convergence and subduction are widespread along Pacific margins, so trenches occur there. In exams, link the Pacific with destructive boundaries.

Correct answer: C. It provided physical evidence for a dynamic Earth

Sea-floor spreading proved Earth's dynamism through magnetism, age, and heat-flow evidence. In exams, treat it as a foundation of modern plate tectonics.

Correct answer: A. Convection currents are part of a possible energy-driven system of plate motion

Convection currents explain movement of energy and material in the mantle. In exams, treat them as an internal process related to plate motion.

Correct answer: B. Divergent boundary

New crust forms at divergent boundaries, especially at mid-oceanic ridges. In exams, link construction with spreading.

Correct answer: C. Greater density makes it able to sink

Old oceanic crust becomes cooler and denser, allowing subduction. In exams, connect density with destructive boundaries.

Correct answer: B. Because it provided measurable physical evidence from the ocean floor

Matching margins were clues, but ocean-floor ages and magnetic stripes were direct measurements. In exams, distinguish clues from measurable evidence.

Correct answer: A. History of polarity reversals and continuous new crust formation

The stripes record Earth's magnetic reversals and successive formation of new crust. In exams, understand this as a marine magnetic time sequence.

Correct answer: B. Distance from ridge and age of rocks

Distance and age can be used to estimate average spreading rate. In exams, remember the distance-age relation for rate.

Correct answer: C. When creation rate differs from destruction rate

A difference between creation and destruction rates can widen or narrow an ocean. In exams, link ocean-basin shape with plate balance.

Correct answer: A. It supplied a possible driving mechanism

Holmes suggested that mantle movement could drive continental motion. In exams, remember it as a causal mechanism.

Correct answer: B. Plate tectonics theory

Plate tectonics explained the movement of both continents and ocean floors within one framework. In exams, treat plate tectonics as the broader explanation.

Correct answer: C. Ridge is constructive and trench is destructive

New crust forms at ridges, while old crust is destroyed at trenches. In exams, remember this construction-destruction pair.

Correct answer: A. Sea-floor spreading

Increasing sediment and rock age with distance indicates spreading. In exams, link age increase with distance from the ridge.

Correct answer: B. Melting and magma related to a subducting plate

With subduction, material melts to form magma, which can create island arcs. In exams, connect trenches and island arcs within the subduction system.

Correct answer: C. As active geological zones of creation and destruction

This concept showed ocean floors as regions of active plate boundaries. In exams, view oceans as dynamic geological systems.

Correct answer: A. Convection gives possible force, spreading shows the process, and paleomagnetism gives evidence

Together, these three strengthen the explanation of plate motion in post-drift studies. In exams, remember this trio as force, process, and evidence.

Correct answer: A. Slab pull and ridge push

Modern explanation understands plate motion through the combined effects of mantle convection, slab pull, and ridge push. In exams, remember the combined mechanism rather than only one force.

Correct answer: A. Identification of new ocean-floor features

Ocean-floor studies identified features such as mid-oceanic ridges and trenches. For exams, connect this with evidence for plate tectonics.

Correct answer: B. Mantle

Convection currents are considered to occur in the mantle due to temperature differences. Remember the mantle as the base of plate movement in exams.