What Is an Abyssal Plain?

An abyssal plain is a deep undersea area created by sediments overlaying a rocky crust, and they are the flattest places on Earth. Abyssal plains cover one-third of the Earth's surface, as much as all land above water, and they sit near continental borders and underwater mountain ranges. Most abyssal plains are in the Atlantic Ocean, with fewer in the Indian Ocean and fewer still in the Pacific Ocean.

Abyssal plains are incredibly flat and are composed of sediment averaging more than one-half-mile thick. It is believed that most of this sediment comes from erosion on land that is washed into the ocean. This sediment settles on uneven oceanic crust more than 10,000 feet deep, filling in any gaps and creating a flat surface.

At the extreme depths of abyssal plains, water pressure is enormous, temperatures are near freezing, and it is dark. Even so, many organisms live on the abyssal plains. They typically eat what is known as marine snow, which is made up of fragments of dead bodies and feces from organisms living far above them that slowly drift down to the surface of the abyssal plains. Organisms that live on the abyssal plains have extremely slow metabolisms and can go for months without eating.