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The Earth’s crust is made

up of the continents

and the ocean basins.

Oceanic crust, which consists of

basaltic rock, is

thinner and denser than continental crust, which

contains granitic

rock; because of

this, the continents rise above

the oceans.

Did You Know

• On average, continents are about 0.5 miles (0.8 kilometers) above sea level, while the ocean floor is about 2.4 miles (3.8 kilometers) below sea level. While continental crust is about 22 miles (35 kilometers) thick, oceanic crust is only about 4 miles (7 kilometers) thick.

A continental margin is a

part of ocean basin that is adjacent to continent. It includes the continental

shelf, a sloping

section of material lies

on top of continental

crust

If seawater recedes and continental

crust is exposed,

some of the continental shelf may become part of

a coastal plain.

Continental

Margin

Deep Ocean Basins

Eventually, the continental shelf or continental rise leads to a deep ocean basin. Comprising 30 percent of

the Earth’s surface, the deep ocean basins contain flat abyssal plains, deep ocean trenches and submerged volcanoes known as seamounts.

Abyssal Plains

Abyssal plains are about 2.5 miles (4 kilometers) below sea level. They are made of volcanic rock that is covered with very thick layers of sediment. Over time,

this sediment has spread out and flattened, making abyssal plains the flattest places on earth.

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