Question

Choose the best answer to each of the following. Explain your reasoning with one or more complete sentences. Plate tectonics is best described as a process that (a) recycles rock between Earth's surface and upper mantle; (b) brings metal from Earth's core to the surface; (c) allows continents to plow through the crust.

Short answer

The best answer is (a) 'recycles rock between Earth's surface and upper mantle.'

Step-by-step solution

Understand Plate Tectonics

Plate tectonics is the scientific theory explaining the movement of the Earth's lithosphere, which is divided into tectonic plates. These plates move over the semi-fluid asthenosphere beneath the crust. This movement is responsible for various geological phenomena, such as earthquakes, volcanic activity, and the creation of mountain ranges.

Analyze Option A

Option (a) 'recycles rock between Earth's surface and upper mantle' is a process known as the rock cycle, which is intrinsically linked to plate tectonics. Tectonic activity causes processes such as subduction and seafloor spreading, which recycle and renew the materials of the Earth's crust and upper mantle.

Analyze Option B

Option (b) 'brings metal from Earth's core to the surface' is not typically a function of plate tectonics. The core of the Earth is composed primarily of metal (iron and nickel), but tectonic processes do not transport these core materials to the surface. Instead, tectonic plates mainly interact within the crust and upper mantle.

Analyze Option C

Option (c) 'allows continents to plow through the crust' is incorrect. Continents are part of these tectonic plates and they do not 'plow through' the crust. Instead, they move as part of the plate on the fluid asthenosphere.

Choose the Best Answer

Considering the explanations of each option, the best description of plate tectonics is (a) because it accurately reflects the recycling of rock materials due to tectonic processes such as subduction and seafloor spreading, aligning with the actions of the rock cycle.

Key concepts

Rock Cycle

The rock cycle is a continuous and dynamic process that describes how rocks transform from one type to another. This cycle has no starting or ending point and is powered by Earth's internal heat and surface processes. There are three main types of rocks involved in this cycle:

• Igneous rocks: Formed from the cooling and solidification of magma or lava.
• Sedimentary rocks: Created from the compaction and cementation of sediments over time.
• Metamorphic rocks: Formed when existing rocks are subjected to high heat, pressure, or chemically active fluids.

Tectonic plate movements greatly influence the rock cycle, facilitating processes like subduction and mountain building. These movements can cause rocks to melt into magma, be uplifted, or undergo metamorphosis. The rock cycle is integral because it recycles Earth's materials, keeping the crust dynamic and allowing for the creation of new landforms.

Tectonic Plates

Tectonic plates are massive slabs of Earth's lithosphere that fit together like a jigsaw puzzle covering the planet's surface. Their movement is driven by the heat from Earth's core, which causes convection currents in the semi-fluid asthenosphere below the plates.

• Boundaries: The interaction between plates occurs at three primary types of boundaries.
• Convergent boundaries: Plates push towards each other, often causing subduction or mountain formation.
• Divergent boundaries: Plates move apart, leading to seafloor spreading and the creation of new crust.
• Transform boundaries: Plates slide horizontally past one another, resulting in earthquakes.

The movement of tectonic plates is responsible for shaping Earth's geographical features, such as continents, ocean basins, mountains, and earthquakes, all of which are manifestations of their ongoing dance on the planet's surface.

Subduction

Subduction is a specific geological process that occurs at convergent boundaries where one tectonic plate sinks below another into the mantle due to its higher density. This process is a key part of the rock cycle and plays a significant role in recycling Earth's crust.

• As a plate descends, it melts due to the high heat and pressure in the mantle, contributing to the formation of magma.
• The magma can then rise through volcanic eruptions, adding new material to the Earth's surface.
• Subduction zones are often associated with intense geological activity such as earthquakes and volcanic arcs.

This recycling process ensures that the crust is continually renewed, supporting dynamic geological conditions necessary for earth shaping and forming diverse ecosystems.

Earth's Crust

The Earth's crust is the outermost layer of our planet and is the solid shell upon which we live. It is incredibly thin in comparison to the other layers of the Earth, like the mantle and core.

• The crust is divided into two types:
• Continental crust: Thicker and less dense, primarily composed of granitic rocks.
• Oceanic crust: Thinner and denser, mainly made up of basaltic rocks.
• The varying thickness and composition of the crust influence tectonic plate behavior.

Tectonic activities, such as the movement of plates, earthquakes, and volcanic eruptions, occur mostly at the crust. Understanding the dynamics of the Earth's crust is essential for explaining phenomena related to plate tectonics and their broader impacts on the planet.