Explore the Ocean Depths

Our planet is called "Earth," but a more accurate name might actually be "Ocean"! Oceans and seas cover over 70% of the planet's surface, but because they support life at much greater depths than land, they actually make up 99% of all the earth's habitable space. The oceans are also what makes land habitable for us, even if we don't live on the coast. For example, the rain that falls on your town evaporated from the ocean and half of all the oxygen you breathe is produced in the oceans. (They are full of microscopic plants called phytoplankton that produce oxygen by the process of photosynthesis.)

If you've ever spent time at the beach, you know that the ocean is immense and powerful. Have you ever wondered what it's like deep below the surface? What the land looks like at the bottom? What kind of creatures live there? And what it would be like to go see for yourself?

Ocean Floor

If you're swimming at the beach, you aren't standing on the ocean floor. The land that juts out from the edges of each continent is called the continental shelf. This shelf can be very short, or it can extend hundreds of miles out into the ocean. The continental shelf drops off down a steep continental slope which leads down to the real ocean floor, called the abyssal plain. The abyssal plain has its own stunning geography: the tallest mountains, longest mountain ranges, and deepest canyons in the world.

Along underwater mountain ranges are openings in the ocean floor that spew out superheated water with toxic concentrations of minerals. These underwater geysers are called hydrothermal vents. Ocean water seeps into cracks in the ocean floor and becomes heated by the magma (liquid rock) beneath the earth's crust. The hot water (sometimes 750˚F) pours back out of the vents, and as it meets the cold 35˚F deep sea water, its dissolved minerals precipitate out - become solid again. These minerals often build up to form towering chimneys. The "Godzilla" chimney off the coast of Oregon grew to be as tall as a 15-story building before it fell over! It is now rebuilding again.

Deep Sea Creatures

You might not expect anything to live near hydrothermal vents. In the first place, they are usually more than 7,000 ft (1.3 miles) below the surface. At this depth the water pressure is extreme - it would crush us in no time at all! In addition, the temperature near a vent fluctuates drastically between hot vent water and cold sea water. There is no natural light this deep in the sea; it is darker than the darkest midnight on land. The water spouting from the vents is full of toxic chemicals and minerals. How can anything live in such a harsh environment?

Despite the odds, hydrothermal vents support a lot of life! They teem with 5-inch-long white vent crabs that eat deep sea worms and mussels. These crabs are designed to withstand the tremendous water pressure. When scientists bring them up to the surface to study them, they die unless they are put in pressurized tanks. The ocean floor has too much pressure for us, but the surface doesn't have enough pressure for vent crabs!

Hydrothermal vents are also home to fields of 8-foot-long tubeworms, worms with bright red plumes that live in tough white tubes made of chitin, the same substance crab shells are made of. Tubeworms have no mouth or stomach, so how do they stay alive? They host bacteria inside their bodies that convert the toxic chemicals from the vents into food. This conversion process is called chemosynthesis, and is unique to the vent ecosystem. Life on land and in the upper reaches of the ocean is supported by energy from the sun through photosynthesis. No sun can reach the bottom of the sea, so chemosynthesis must take its place for many deep sea creatures to survive.

Other creatures live deep in the sea beneath the reach of sunlight. Many of these survive by creating their own light through a chemical reaction. This type of light is called bioluminescence. Bioluminescent animals use their light to find food and mates. Some species, like the anglerfish, dangle a lighted "lure" from their bodies. Other fish think this lure is food, but when they try to eat it, the anglerfish eats them instead! (Click here to see a picture of an anglerfish.)

Exploring the Deep

There is only one way to explore the very bottom of the sea - in an underwater craft called a submersible. Humans can dive down to depths of 130 feet if they use SCUBA equipment (self-contained underwater breathing apparatus). With extra special equipment and training they can go down to 300 feet. But the average depth of the ocean floor is around 12,000 feet and in some places much deeper!

Exploration with submersibles began with vehicles called bathyspheres in the 1930s. These were simply steel balls lowered from a ship with two people inside. They couldn't maneuver on their own, and they couldn't collect samples. To overcome these limitations, bathyscaphs ("deep boats") were developed. The most famous bathyscaph is the Trieste. While it was large and not very easily maneuverable, the Trieste made the deepest dive in history: in 1960 it dove to "Challenger Deep," the deepest part of the Mariana Trench near Japan. The water pressure at this spot is eight tons per square inch! No one will break the Trieste's record of diving 35,810 feet (almost seven miles) because that happens to be the deepest point on the planet. If you set Mt. Everest down on the bottom of Challenger Deep, there would still be more than a mile of water above it!

Five years after the Trieste's deep dive, the "deep submergence vehicle" Alvin made its first dive. This craft has three windows and can carry two scientists and a pilot. It is easy to maneuver and is fully outfitted with lights, video cameras, clawed arms, temperature probes, and more. Since 1965 Alvin has made more than 4,000 dives carrying scientists that study the geology, biology, and chemistry of the deep ocean. This submersible discovered life at hydrothermal vent sites almost 30 years ago, recovered a hydrogen bomb accidentally dropped in the Mediterranean Sea, and has explored the wreck of the Titanic. It continues today to study the creatures of the deep. Read about an expedition the Alvin took in 2000 and see videos and pictures of hydrothermal vents at this Voyage to the Deep website.

In spite of exploration with manned submersibles like Alvin and unmanned remote-controlled submersibles, the deep ocean is still a vast territory of unknowns. There is work to be done for deep-sea explorers for many years to come!

Tide Pools Lesson for Grades PreK-2

Introduce your young children to the many incredible creatures that dwell in the oceans of the world, whether you live near one or not! This Teaching Tip focuses on shoreline tide pools and can be used as a science lesson for teaching kids about plant and animal life most commonly found in them.

• Click here to read the rest of the article

Make a Cartesian Diver

How can scuba divers and submersibles dive down into the water and then come back up? Find out with this easy project.

Materials:

• 2-liter soda bottle
• medicine dropper
• glass or beaker

Procedure:

1. Fill a glass with water and put the medicine dropper in it. Suck enough water into the dropper so that it just barely floats - only a small part of the rubber bulb should be out of the water. This is your diver, and it has neutral buoyancy. That means the water it displaces (pushes aside) equals the weight of the diver. The displaced water pushes up on the diver with the same amount of force that the diver exerts down on the water. This allows the diver to stay in one spot, without floating up or sinking down.

2. Now that your diver is ready with enough water inside to give it neutral buoyancy, fill the soda bottle all the way to the top with water. (You don't want any air between the water and the cap.) Lower the medicine dropper into it and screw the cap on tightly.

3. Squeeze the sides of the bottle. What happens? The diver sinks. Let go of the bottle and it will float back up. Why does it do this? Watch carefully as you make it sink again - what happens to the air inside the dropper?

As you squeeze the bottle (increasing pressure) the air inside the dropper is compressed, allowing room for more water to enter the dropper. (You'll see the water level in the dropper rise as you squeeze the bottle.) As more water enters, the dropper becomes heavier and sinks. Practice getting just the right amount of pressure so your diver hovers in the middle of the bottle.

Submarines and submersibles have ballast tanks that fill up with water to make them dive. When it's time to surface, air is pumped into the tanks, forcing the water out and making the sub float to the top. Read more about submarines here. Scuba divers wear heavy belts of lead to make them sink in the water, but they also have a buoyancy compensator. This is a bag that they inflate with air from their oxygen tank. When it is inflated, it causes them to float up to the surface. While underwater they'll put just enough air in the bag to keep them from floating or sinking.

Of course, most subs and scuba divers are diving in salt water. Try your diver again in a bottle of salt water. Is there any difference in the way it works? Do you need to start out with more water in the dropper than you did before? Remember that salt water is denser than fresh water!

• Ready for another project? Read about blue whales below, and then do this Blubber Experiment to see how blubber helps keep whales warm in cold water!

Science Spotlight: The BIG Blue Whale

If someone asked you what the biggest animal in the world is, what would you say? You might say an elephant, and that would be a good guess. The African elephant is the biggest land mammal, weighing nearly 14,000 pounds, or seven tons. That's pretty big, but it's nothing compared to the largest animal in the world, which lives in the ocean. The blue whale is so big that its tongue weighs as much as an elephant does! It can grow to be over 100 feet long and weigh more than 150 tons - 300,000 pounds! Its heart is the size of a small car, and it circulates seven tons of blood in its body. With that size, a blue whale can only live in the ocean. Out of the water, its skeleton would collapse under its own body weight. (To see how long a blue whale really is, get 100 feet of string and a friend. Go outside and stretch the string out between you. Can you imagine a whale that big?)

Blue whales are mammals, not fish. This means they have lungs instead of gills, and have to come up to the surface of the ocean to breathe. While our bodies breathe automatically, blue whales can choose when to breathe - they usually take a breath 1-4 times per minute, but they can hold their breath for almost an hour. (Usually their dives only last 10-20 minutes, though.) When they need to take a breath they come to the surface and blow air and water out of their two blow holes before taking a new breath. The spray from their blow holes can reach as high as 30 feet!

Because they are mammals, blue whales also have live babies and feed them milk - lots of milk, in fact. A baby blue whale drinks 50-100 gallons of milk per day and gains around eight pounds an hour.

Not only are blue whales the largest creatures in the world, they are also the loudest. Their low-frequency whistle can reach 180 decibels, which is louder than a jet engine. Scientists think the whales use their whistle to find mates and possibly use it to navigate by listening to the echoes that bounce off the ocean floor.

The population levels of blue whales decreased disastrously after the invention of harpoon guns in the mid-1800s. They are now an endangered species and hunting them is illegal. The numbers of these enormous and fascinating creatures are growing again.

Fabulous Facts

Pacific Planet. The Pacific Ocean is the biggest and deepest of the world's oceans. It covers 1/3 of the earth's surface and has an average depth of over 15,000 feet.

Water That Won't Boil. The water pouring from hydrothermal vents at the bottom of the ocean can be as hot as 750˚F, but it doesn't boil. Water on your stove boils at 212˚. So what's the difference? The water on the ocean floor is under tremendous pressure from the miles of water above it, which prevents it from boiling. The higher the pressure, the higher the boiling point.

Highest vs. Tallest. Have you heard that Mt. Everest is the tallest mountain in the world? That isn't quite true. At 29,035 feet above sea level, it is certainly the highest mountain. But if you measure a mountain's size from base to peak instead of from sea level, then the tallest mountain is actually Mauna Kea in Hawaii, at 33,476 feet. You can't see how big it is, though, because most of it is underwater!

Science Links

Check out the creatures of the deep sea with this online field guide.

Watch some live action on the underwater web cams at the Monterey Bay Aquarium!

See pictures of the largest animal in the world - the blue whale.

Watch videos from the ocean floor and read how marine biologists do research on board the deep submergence vehicle Alvin.