Post-drift studies and Convectional Current Theory

Wegener's evidences were important but the driving force was weakly explained. Exam tip: separate evidence and mechanism.

Holmes linked mantle convection with movement of landmasses. Exam tip: treat it as a possible solution to Wegener's weakness.

Thermal difference creates density difference and starts a convection cycle. Exam tip: remember hot rises and cool sinks.

Mantle movement is slow but effective over long time. Exam tip: remember the geological time scale.

Ocean-floor mapping helped understand the dynamism of Earth's surface. Exam tip: do not treat the ocean floor as flat.

Upwelling material near ridges is linked with new ocean floor. Exam tip: understand ridges as spreading zones.

Trenches are deep parts and may be linked with downward movement. Exam tip: remember trenches with sinking.

Seafloor spreading challenged the idea of a fixed ocean floor. Exam tip: treat it as post-drift evidence.

Radioactive decay can generate heat inside Earth. Exam tip: treat internal heat as the basis of convection.

Age of ocean floor helps understand direction and development of spreading. Exam tip: remember the relation between age and ridge.

Earthquakes and volcanoes are linked with active zones of Earth. Exam tip: also connect their distribution with plate boundaries.

In a convection cell hot material rises and cool material sinks. Exam tip: understand it as a cycle.

Convection currents provided a way to link plate movement with mantle motion. Exam tip: understand it as background to plate tectonics.

Convection is movement caused by differences in temperature and density. In the mantle, warmer material tends to become less dense and move upward, while cooler, denser material tends to move downward. This continuous contrast can help produce convection currents. If the mantle had no thermal difference, this driving force would be greatly reduced, so the formation or strength of convection currents would decrease.

Option A is therefore the best answer. Option B gives the opposite effect, because removing a thermal contrast would not immediately make convection faster. Options C and D are also too extreme: the ocean floor would not simply disappear, and earthquakes would not necessarily stop completely. The question asks specifically about convection currents, so the direct effect of losing the temperature difference is reduced convection.

In seafloor spreading ridge zones are centers of formation and spreading. Exam tip: connect ridges with spreading.

In subduction material may move from surface toward interior. Exam tip: remember trenches as sinking zones.

Direct answer: Option A, the idea that the ocean floor is completely flat and inactive. Ocean-floor ridges are long elevated underwater features, while trenches are deep narrow depressions. Their discovery showed that the sea floor has varied relief and is connected with geological activity. This evidence weakened the old oversimplified belief that the ocean floor was an unchanging, level surface. Option A is correct because ridges and trenches directly contradict “completely flat and inactive.” Option B is wrong because the presence of water over the ocean floor is an obvious condition, not an idea weakened by discovering landforms beneath it. Option C is wrong because rocks on continents are unrelated to the specific conclusion about ocean-floor relief. Option D is wrong because gravity is not challenged by the discovery of ridges and trenches. Reasoning: underwater features were observed; therefore the floor is not uniformly flat; geological processes must be considered. Memory cue: ridges rise and trenches sink, so the sea floor is not a flat sheet.

Mantle material may behave rigidly but can move slowly over geological time. Exam tip: understand the importance of long duration.

Post-drift studies linked movement with a broader Earth system. Exam tip: write the relation between surface and interior.

Direct answer: Option A, convection cycle. In convection theory, heating creates density differences. Warmer, less-dense material rises, while cooler, denser material descends. These two opposite movements are not separate unrelated events; together they complete a repeating circulation. That repeating circulation is called a convection cycle or convection cell. Option A is therefore correct. Option B, river delta, forms where a river deposits sediment, usually near its mouth; it is not produced by rising and sinking currents. Option C, glacial lake, is formed by ice-related erosion or melting and has no connection with this mechanism. Option D, desert dune, is a wind-shaped deposit of sand, not a heat-driven internal circulation. The reasoning is: heat causes rising, cooling causes sinking, and the two movements together make a cycle. Exam cue: rising plus descending material equals convection cycle.

Marine geology helped understand the dynamism of the ocean floor. Exam tip: link it with ocean-floor study.

Mantle currents can affect the plates lying above. Exam tip: understand influence from mantle to plate.

Internal heat can link mantle and ocean-floor processes. Exam tip: write the relation between interior and surface.

Study of ocean floor was very useful in new understanding of continental movement. Exam tip: connect ocean-floor study with post-drift.

Post-drift topic explains developments after Wegener. Exam tip: write later evidence and mechanism.