Geology and Earth Structure

Sea-floor spreading occurs at mid-ocean ridges, where divergent tectonic plates pull apart, allowing magma to rise and form new oceanic crust. Deep ocean trenches are where old crust is subducted and destroyed, not where spreading occurs.

The theory of plate tectonics explains the structure of the Earth's lithosphere and the forces, such as convection currents in the mantle, that drive the movement of tectonic plates. Continental drift was the historical predecessor that lacked a mechanism for how the plates moved.

The lithosphere is the rigid, outermost shell of Earth, consisting of the crust and the solid, uppermost portion of the mantle. The asthenosphere lies directly below the lithosphere and is semi-fluid.

The asthenosphere is the highly viscous, mechanically weak, and ductile region of the upper mantle, lying just below the lithosphere. Therefore, it is located entirely within the mantle.

Counting from the outside of the Earth inward, the layers are the crust (first), mantle (second), outer core (third), and inner core (fourth). The inner core is the solid, extremely hot center of the Earth.

Counting from the outside inward, the third layer of the Earth is the liquid outer core, which lies between the mantle and the solid inner core.

Counting from the outside inward, the second layer of the Earth is the mantle, which makes up the bulk of Earth's volume and lies between the crust and the outer core.

The Earth is divided into several layers based on its composition and physical properties. The outermost layer, which we live on, is the crust. It is the thinnest and first layer of the Earth, followed by the mantle, outer core, and inner core.

A plateau is a flat-topped highland area that rises sharply above the surrounding land on at least one side. It is also commonly referred to as a tableland.

A subcontinent is a large, distinct landmass that is part of a larger continent but is geographically or geologically separated from it. India is a classic example of a subcontinent because it is separated from the rest of Asia by the Himalayas.

Subduction is the geological process that takes place at convergent boundaries where one tectonic plate moves under another and sinks into the mantle. This process is responsible for forming deep ocean trenches and volcanic belts. The other options are non-geological terms.