Post-drift studies and Convectional Current Theory

Correct answer: B. Decay of radioactive elements

Holmes related mantle convection to heat produced by radioactive decay inside Earth. Remember that the heat source is internal.

Correct answer: C. Mid-oceanic ridges and magnetic stripes

Mid-oceanic ridges and symmetrical magnetic stripes support the creation of new ocean floor. In exams, connect them with seafloor spreading.

Correct answer: D. Rising and sinking currents in the mantle

Thermal differences in the mantle cause material to rise and sink. This cyclic motion is considered helpful in moving plates.

Correct answer: A. New ocean floor is spreading on both sides of the ridge

Symmetrical age distribution is an important sign of seafloor spreading. In exams, read the age pattern with distance from the ridge.

Correct answer: B. Subduction

Trenches generally form where an oceanic plate sinks beneath another plate. Link this with convergent boundaries.

Correct answer: C. Because they provided direct geophysical evidence

Ocean-floor relief, age and magnetism gave stronger evidence than simple shape matching. In exams, emphasize direct evidence.

Correct answer: D. It suggested an internal mechanical basis for continental movement

Holmes tried to explain continental movement through mantle convection. This idea became a basis for later plate tectonics.

Correct answer: A. Old ocean floor is destroyed by subduction

Oceanic crust forms at ridges and is destroyed at trenches. Therefore, very old ocean floor is rare.

Correct answer: B. Magnetic reversals of Earth and seafloor spreading

Cooling lava preserves the magnetic field of its time. Matching stripes on both sides show spreading.

Correct answer: C. Hot magma rises and forms new crust there

The direct answer is C, hot magma rises and forms new crust there. A mid-oceanic ridge is a long underwater mountain chain formed where oceanic plates move apart. When the plates separate, hot mantle material or magma rises into the gap. It cools and becomes new oceanic crust, so heat is coming upward from below and the measured heat flow is high. The fact chain is: plates diverge → hot material rises → new crust forms → high heat flow. Option A, higher wind speed, concerns the atmosphere and does not heat the deep ocean floor. Option B, river deposition, occurs where rivers bring sediment, mainly near coasts and deltas, not as the main ridge process. Option C is correct because rising hot magma directly brings internal Earth heat toward the sea floor. Option D, melting glaciers, is a surface climate process and does not explain heat from the oceanic crust. Memory cue: ridge means rising magma, spreading, new crust and high heat.

Correct answer: A. Guyot

A flat-topped seamount is called a guyot. It is linked with older erosion and sea-level indicators.

Correct answer: C. They combine ocean-floor relief, rock age and magnetism

Later evidence was multi-layered and linked with ocean floors. In exams, writing three evidences together strengthens the answer.

Correct answer: D. Rising current and divergent boundary

A rising hot current may pull crust apart and form a divergent boundary. It is linked with mid-oceanic ridges.

Correct answer: A. Because oceans preserve direct signs of plate movement

The ocean floor showed ridges, trenches, magnetic stripes and rock-age patterns. These made movement clearer.

Correct answer: B. New crust forming at trenches

New oceanic crust forms at ridges, not at trenches. Trenches are linked with subduction and destruction.

Correct answer: C. Sinks downward

In a convection cell, cooler material becomes relatively denser, so it sinks downward. In contrast, hotter and less dense material rises upward. Arthur Holmes considered such convection currents in the mantle as a possible cause of continental movement. Exam tip: in convection, hot material rises and cool material sinks.

Correct answer: D. It indicates crustal movement through ancient magnetic fields preserved in rocks

Palaeomagnetism reads ancient magnetic signals stored in rocks. It helps understand past positions and movement of plates.

Correct answer: A. Seafloor spreading

New rocks form at ridges, while older rocks occur farther away. This is the common age pattern of spreading.

Correct answer: B. Its slow flow-like behaviour over long time

The mantle behaves like a very slow-flowing material over geological time despite being solid-like. This makes convection explanation possible.

Correct answer: C. Wegener gave evidence, Holmes suggested a possible internal driving force

Wegener had a weak explanation for the force of movement. Holmes tried to fill this gap through mantle convection.

Correct answer: D. Ocean floors are inactive and uniform

Ridges, trenches and seamounts showed that ocean floors are active and varied. This was important for later tectonic explanation.

Correct answer: A. Earth's total size remaining nearly balanced

Creation at ridges and destruction at trenches prevent abnormal expansion of Earth. This is a balance in plate tectonics.

Correct answer: B. Young basaltic rocks near ridges

Young basaltic crust near ridges is direct evidence of new ocean floor formation. This is a key fact of seafloor spreading.

Correct answer: C. When sinking currents create a convergence zone

A sinking current can help draw material inward and bring plates together. This links convergent boundaries with subduction.

Correct answer: D. Continental evidence such as coastline, fossils and rock similarity

Wegener's continental evidence was strengthened later by ocean-floor and geophysical evidence. In exams, write the difference between old and new evidence.