Exploring the Ocean:
Exploring the Ocean Floor
 People have studied the ocean since
ancient times, because the ocean provides
food and serves as a route for trade and
travel.
 Modern scientists have studied the
characteristics of the ocean’s waters and
the ocean floor. This is called
oceanography.
 Humans cannot survive the darkness, cold
temperatures, and extreme pressure of the
deep ocean. So scientists have had to
develop technology to study the ocean floor.
 A major advance in ocean-floor mapping
was sonar, which stands for sound
navigation and ranging.
 Sonar is a system that uses sound waves to
calculate the distance to an object. The sonar
equipment on a ship sends out pulses of
sound that bounce off the ocean floor.
 The equipment then measures how quickly
the sound waves return to the ship.
 Sound waves return quickly if the ocean
floor is close.
 Sound waves take longer to return if the
ocean floor is farther away
Features of the Ocean Floor
 If you could travel along the ocean floor,
you would see the continental shelf, the
continental slope, the abyssal plain, the
mid-ocean ridge, and a trench.
Shallow Water:
 The continental shelf, a gently sloping, and
shallow area of the ocean floor that extends
outward from the edge of a continent.
 The steep edge of the continental shelf is
called the continental slope. The
continental slope marks the true edge of a
continent, where the rock that makes up the
continent stops and the rock of the ocean
floor begins.
Open Ocean:
 The smooth, nearly flat region of the ocean
floor is called the abyssal plain.
 The mid-ocean ridge is a continuous range
of mountains that winds around Earth, much
as the line of stitches winds around a
baseball. The mid-ocean ridge passes
through all of Earth’s oceans. Nearly
80,000 kilometers long, it is the longest
mountain range on Earth.
Deepest Depths:
 A canyon in the ocean floor called a trench,
which is so deep you cannot see the bottom.
Review Questions:
1. What is sonar and how does it work?
- Sonar is sound navigation ranging. Sound
waves are bounced off of the ocean bottom
and the travel times are used to calculate the
depth of the ocean floor.
2. List the main sections of the ocean floor.
- Continental shelf, continental slope, abyssal
plain, mid-ocean ridges, trench.
3. Briefly describe each of the ocean floor
characteristics.
- continental shelf: shallow, gently sloping
edge of continent
- continental slope: more steeply sloping
edge of continent
- abyssal plain: flat, deep ocean bottom
- mid-ocean ridge: long range of high
underwater mountains
- trench: underwater canyon in ocean floor