The inquisitive explorers pilot their tiny ship into an alien world never before seen by humans. Outside the ship's strong hull is a hostile environment. It is pitch dark, with crushing pressures and cold that would kill a human in seconds.
As they navigate with cameras, sensors, and special radar, the ship's powerful spotlights illuminate an awesome landscape. Huge clouds of scalding-hot water filled with poisonous chemicals billow from a volcano-like hole. Weird creatures live nearby. Among them are huge red tube worms that have no mouth, stomach, or intestines; giant clams; and blind shrimp.
The pilots use a robot arm, like that on the space shuttle, to collect samples. Then they deploy a small robot vehicle from the mother ship to take close-up pictures and do other studies. Chances are they will discover life-forms never before seen on Earth.
These are not astronauts exploring a planet in deep space. Rather, they are underwater explorers who have traveled to Earth's last frontier the deep sea. In some ways, we know more about the moon than we know about Earth's own oceans. The oceans or seas cover about 71 percent of Earth's surface. Yet the oceans have not been thoroughly explored. That is especially true of deeper parts of the ocean, which reach a depth of 36,198 feet (11,033 meters).
An Extreme Environment
Earth's oceans are not welcoming to visitors from the land. Underwater explorers face the same kinds of difficulties as astronauts in space. They must take along their own air supply and protect their bodies from dangerous pressures and temperatures. On Earth's surface, the weight of the atmosphere puts 14.7 pounds of pressure on every square inch of the human body. People are used to living at that pressure. In the water, pressure on each square inch of the body increases about a half pound for every foot of water. A diver 2,000 feet (610 meters) beneath the sea would experience pressure of more than 1,000 pounds over every square inch of the body. Such crushing pressure would instantly kill a person on land.
As depth increases, the water becomes colder. In deep water near the ocean floor, and surface water near the North and South Poles, water temperature is close to freezing. (The freezing point of seawater is about 28.4°F (-2°C) instead of the 32°F (0°C) freezing point of fresh water.) But water does not have to be that cold to harm humans. Even water at mild temperatures quickly drains heat away from the body. A human can survive only a few minutes in chilly 40 to 50°F (4 to 10°C) water.
The deep ocean is home to strange-looking creatures whose bodies are adapted to life in the dark at crushing pressures. Some have no eyes because there is nothing to see in the pitch darkness, while others have huge eyes to gather the faintest light rays. Some deep-sea animals have their own "spotlights." Their body surfaces have light-producing organs called photophores. The flashes of light are used to confuse predators or to illuminate an area to find prey. Certain fish have evolved internal structures called swim bladders gas-filled bags that keep their insides at the same pressure as the outside environment.
Some of the most interesting deep-sea creatures are those living near underwater hot springs, called hydrothermal vents, on the seafloor. In 1979 vents were discovered on the seabed of the Pacific Ocean near the Galápagos Islands by a team of American scientists, led by Robert Ballard, exploring in the research vessel Alvin. The water around the vents was hot enough to melt the plastic on Alvin's sensors! Even so, the explorers found a rich variety of life living nearby.
Very hot water rich in dissolved minerals pours out of the vents from underneath the ocean floor. The hot water cools quickly, and the minerals drop in the water and settle around the vent opening, gradually forming chimney-like towers that can reach a height of 3 1/2 miles (6 kilometers). Blind crabs, giant clams, and bright red tube worms living in darkness depend on the hot water for survival in their dark, deep world. Bacteria around the vents use chemicals in the water to make energy and grow just as plants in shallow water use sunlight for photosynthesis. Other creatures around the hydrothermal vents rely on the bacteria for food.