Joan Cartan-Hansen, Host: Oceans cover more than 70 percent the earth's surface.

Come and explore what you'll find under the sea.

♪ (MUSIC) The earth is covered with water.

There's really only one ocean covering about 70 percent of the earth's surface.

To make things easier, we've given geographical names to different parts of this vast body of water.

There is the Pacific, the Atlantic, the Indian, the Southern, and the Arctic Oceans.

And just because it's one Ocean doesn't mean it's all the same.

Ocean waters exist in layers.

The deeper the water, the more cold the water is.

Most ocean life lives in the shallower areas of the ocean where sunlight can penetrate.

A few creatures live very deep in the ocean.

Many have to make their own light so they can find food and attract a mate.

There is an amazing variety of life in the ocean, everything from mammals to fish to crustaceans to even zooplankton, which are one-celled animals.

Student: Much of life in the ocean is invisible to the naked eye.

For instance, if you ever swallowed a milliliter of ocean water you've also gulped one million bacteria and ten million viruses.

Give or a take a few.

Cartan-Hansen: Water in the Ocean is salty.

The salt comes from minerals in the earth's crust.

Water erodes the crust, and the minerals collect in the Ocean.

The ocean floor is the area between the water and the earth's crust.

It's covered in sediments created by water moving and wearing down the rocks and minerals.

The part that's closest to the shore is called the continental shelf.

Beyond that is the continental slope and then the abyssal plain.

That part of the ocean can get very deep.

The Mariana Trench in the Pacific Ocean is the ocean's deepest point at more than 36,000 feet deep.

Student: Earths longest mountain range is the mid-ocean ridge more than 50 thousand kilometers in length.

It winds around the globe from the Arctic Ocean to the Atlantic, skirting Africa, Asia, Australia and crossing the Pacific to the west coast of North America.

It is four times longer than the Andes, Rockies and Himalayas combined.

Cartan-Hansen: Water in the ocean moves in three basic ways.

First, there are the currents.

Currents are like rivers within the ocean.

The water moves because of changes in temperature and because of the turning of the Earth on its axis.

Currents in the Northern Hemisphere move clockwise and currents in the Southern Hemisphere move counterclockwise.

Currents affect the earth's weather and climate.

Creatures like birds and whales use currents to migrate, and sailors have used currents for centuries to direct ships.

The second ocean motion are the tides.

Tides are caused by gravitational forces from the Sun and the moon.

The moon's gravity pulls on the water causing it to bulge on the side of the earth closest to the moon.

Water on the opposite side of the earth from the moon bulges, too, because the earth is spinning.

Bulges pull water away from shorelines at sometimes and then pushes it back at others.

Every day, there's a high tide and a low tide, and when the sun lines up with the moon, The tides are more extreme.

Student: The highest tides in the world are at The Bay of Fundy which separates New Brunswick with Nova Scotia.

At some times of the year, the difference between the high tides and low tides is 16.3 Meters.

Taller than a three-story building.

Cartan-Hansen: The third ocean motion is the wave.

Ocean waves happen when the wind blows across the surface of the water and friction pushes the water upward creating a wave.

If you were in the middle of the ocean, you would just bob up and down in the waves, not moving from your original point.

But as you get closer to shore, the waves get compressed against the rising ocean floor.

The waves keep rising until they break and fall down causing a surf.

There's lots of movement in the earth's crust under the ocean.

Landslides, earthquakes and volcanoes can create what's called a tsunami.

That movement causes a tidal wave of tremendous force to hit the shore.

The tsunami in Japan in 2011 killed thousands of people.

90 percent of volcanic activity on the earth happens in the ocean.

Volcanoes erupting can create islands like the islands of Hawaii.

We've only explored about 5 percent of the ocean, but what we know is that it's filled with different types of ecosystems.

The different ecosystems happen because of different water temperatures and water depth.

Coral reefs are one ecosystem, and they're home to 25 percent of marine life.

Coral is an animal structure that anchors to rock and provides food and shelter for lots of other animals and plants.

Sadly, coral reefs around the world are in trouble because of human activity and global warming.

Our oceans are also in trouble because of pollution.

Plastics don't easily degrade, so they can float around in the ocean for years.

Air pollution is responsible for about a third of the contaminants that end up in the ocean, and each year about three times as much trash is dumped into the ocean as the weight of all the fish caught.

There are whole islands of trash in the ocean.

Oceanographers are scientists who study the oceans.

They're helping us understand how we humans are impacting the ocean and what we can do to help.

The ocean is essential to all life on earth.

The ocean creates our weather.

It's key to the earth's water cycle.

We get food from the ocean, and it's home for about 90 percent of all life on earth.

We need to care and appreciate the ocean and all it offers.

If you want to learn more about oceans, check out the Science Trek website.

You’ll find it at ScienceTrek.org.

♪ (MUSIC) Announcer: Presentation of Science Trek on Idaho Public Television is made possible through the generous support of the Laura Moore Cunningham Foundation, committed to fulfilling the Moore and Bettis family legacy of building the great state of Idaho.

By the Idaho National Laboratory, mentoring talent and finding solutions for energy and security challenges, by the friends of Idaho Public Television and The Corporation for Public Broadcasting.