When the Extreme 2001 research team leaves Costa Rica aboard the research vessel Atlantis on October 15, it will take them four days to travel 1,200 miles to their destination in the Pacific Ocean, above a vent field that scientists often refer to only by its latitude, "9°North."

This geologically active area lies along the Mid-Ocean Ridge system, the 40,000-mile mountain range that snakes its way underwater around the globe.

The Mid-Ocean Ridge marks the areas where the Earth's crustal plates are moving apart, giving rise to volcanoes and hydrothermal vents. In fact, volcanic eruptions are so frequent along the perimeter of the Pacific Ocean basin the area is known as the "Ring of Fire."

What Is a Hydrothermal Vent?

A hydrothermal vent is a geyser on the seafloor. It continuously spews super-hot, mineral-rich water that helps support a diverse community of marine organisms.

Hydrothermal vents were discovered in 1977 in the Pacific Ocean. They have since been found in the Atlantic and Indian oceans. Most are located at an average depth of about 7,000 feet in areas where new seafloor is being made. As the gigantic plates that form the Earth's crust move apart, cracks and crevices form in the seafloor. Seawater seeps into these openings and is heated by the molten rock, or magma, that lies beneath the Earth's crust. As the water heats up, it rises and gushes back out onto the ocean floor, creating a hydrothermal vent.

Chimneys top some hydrothermal vents. These smokestacks are formed from dissolved minerals that precipitate (form into particles) when the super-heated vent water -- up to 750°F -- meets the surrounding deep ocean water, which is just above freezing.

"Black smokers" are the hottest of the vents. They spew a toxic stew of metals (mostly iron) and sulfur, which combine to form black minerals called metal sulfides. These minerals give the smoker its black color.

"White smokers" release cooler fluid than their cousins. They typically contain compounds of barium, cal-cium, and silicon, which are white.

Geologists are intrigued by how rapidly vent chimneys grow -- up to 30 feet in 18 months. A scientist at the University of Washington has been monitoring the growth of "Godzilla," a vent chimney in the Pacific Ocean off the Oregon coast. It reached the height of a 15-story building before it toppled and is actively rebuilding.

Why Study the Vents?

There are many reasons why scientists want to learn more about hydrothermal vents. These geysers are believed to play an important role in the ocean's temperature, chemistry, and circulation patterns.

Scientists also are fascinated by the unusual life that inhabits vent sites. These creatures, from eyeless shrimp to towering tubeworms, thrive under some of the most demanding conditions on the planet: high temperature, high pressure, and total darkness. What further distinguishes vent dwellers from other life on Earth is their energy source. They are the only complex ecosystem known to live on energy from chemicals (chemosynthesis) rather than energy from the sun (photosynthesis).

The hydrogen sulfide and other chemicals that rocket out of the vents would be poisonous to most organisms. But exotic animals flourish here thanks to unique adaptations. Some also have a special relationship with the tiniest vent life: bacteria.

While vent crabs and fish prey on other animals for food, vent dwellers such as tubeworms depend on bacteria for survival. These tiny microbes can convert the toxic chemicals released by the vents into food and energy for the worms. Thus, some vent dwellers must either consume bacteria or harbor bacteria in their bodies so that the microbes can make food for them.

Scientists are particularly interested in vent bacteria because these primitive microbes can withstand high temperature and pressure, giving them many valuable uses in industry. For example, some bacteria can convert harmful chemicals to safer forms, making them ideal for cleaning up oil spills and hazardous waste.

Also, some astrobiologists speculate that if there is life on other planets, it might be vent bacteria or a relative. Europa, one of Jupiter's moons, is covered in ice. Recent findings suggest that portions of the ice move, which is strong evidence that liquid water lies beneath it. The water may be maintained in its liquid state by hydrothermal vents. If vents exist on Europa, vent bacteria might live there, too!