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Difficulty: MediumEarth's Interior and Plate Tectonics

Thermal convection within Earth's mantle is the primary driving mechanism behind the movement of tectonic plates. Arrange the stages of a single mantle convection cycle in the correct chronological sequence, beginning with the heating of deep mantle material.

  1. 1Thermal energy from Earth's core heats deep mantle rock, causing it to expand and decrease in density.
  2. 2The hot, lower-density mantle rock slowly ascends toward the upper asthenosphere in a rising thermal plume.
  3. 3As the plume reaches the rigid lithosphere, it cools and spreads horizontally, exerting lateral drag on overlying tectonic plates.
  4. 4The cooled, dense mantle rock and attached subducting lithospheric slabs sink back down toward the core-mantle boundary.

Answer

The correct sequence of mantle convection is: deep heating and density reduction of mantle rock, upward ascent of buoyant mantle plumes, horizontal cooling and lateral flow dragging tectonic plates, and downward sinking of cooled dense rock and subducting slabs.
Mantle convection operates as a continuous thermal heat engine: core heat lowers the density of deep mantle rock, causing it to rise buoyantly toward the asthenosphere. Upon encountering the lithosphere, the flow diverts horizontally, cooling and dragging tectonic plates across the surface. Once sufficiently cooled and dense, the rock and subducted slabs sink back to the deep interior to be reheated, completing the cycle.

Step-by-Step Solution

1
Identify the initial thermal trigger of the convection cycle.
Deep mantle material gains heat from Earth's core, which causes thermal expansion and lowers its density relative to surrounding rock.
Convection in any fluid or ductile solid must begin with uneven heating that alters material density.
2
Trace the path of the heated, lower-density rock.
The buoyant rock rises toward the upper mantle and asthenosphere as a warm convective upwelling.
Lower-density materials naturally experience buoyant upward forces in a gravitational field.
3
Determine the interaction between the upwelling mantle and the lithosphere.
The rising current is diverted horizontally beneath the rigid crust, cooling as it moves and pulling tectonic plates along its flow.
The rigid lithosphere acts as an upper mechanical barrier, forcing horizontal divergence and transmitting shear stress.
4
Complete the convective loop by identifying how cooled material returns downward.
As the mantle material and subducting oceanic crust lose heat, their density increases, causing them to sink back toward the deep mantle.
Cooling creates negative buoyancy (slab pull and convective descent), closing the circulation cell.

Key Concept

Mantle Convection and Plate Motion Driving Forces
Estimated Time:1m 0s
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Topics

Earth's Interior and Plate Tectonics

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