Physical Geology

Hypothesis

An explanation with minimal evidence.

Theory

An explanation supported by significant evidence.

Law

A statement that summarizes relationships.

Nebular Hypothesis

The theory that dust and gases began to gravitationally collapse to form the solar system.

Protosun

The early stage of the sun formed from the gravitational collapse of a nebula.

Chemical Differentiation

The process by which heavy elements sink to the center of a planet while lighter elements rise to the surface.

Crust

The outermost layer of Earth, mainly composed of silicon and oxygen.

Oceanic Crust

A type of crust that is 3-15 km thick, denser (~3.0 g/cm³), and contains less silicon and oxygen.

Continental Crust

A type of crust that is 20-70 km thick, less dense (2.7 g/cm³), and contains more silicon and oxygen.

Mantle

The layer that makes up 82% of Earth's volume, composed of iron, oxygen, silicon, and magnesium.

Core

The innermost layer of Earth, primarily made of iron and nickel, with a density of ~11 g/cm³.

Lithosphere

The solid outer layer of Earth, including the crust and uppermost mantle.

Asthenosphere

The soft, pliable portion of the upper mantle that behaves like playdough due to high temperatures.

Outer Core

The liquid layer of Earth's core, caused by high temperatures.

Inner Core

The solid layer of Earth's core, due to immense pressure.

Continental Margin

The portion of the seafloor adjacent to landmasses.

Continental Shelf

The area of continental crust that is submerged under the ocean.

Continental Slope

The steep drop-off from the continental shelf to the deep ocean.

Continental Rise

A wedge of sediment that accumulates at the base of the continental slope.

Abyssal Plains

Very flat areas of the deep seafloor.

Trenches

Exceptionally deep and narrow parts of the ocean floor.

Seamounts

Small underwater mountains formed by volcanic activity.

Mid-Ocean Ridges

A linear chain of uplifted seafloor formed by tectonic activity.