The deeper you go into Earth's interior, the hotter it gets, The inner core is believed to be as hot as 5,500°C (10,000°F)!

Many of us are familiar with "Old Faithful" in Yellowstone National Park. This famous geyser erupts several times a day. It spouts a column of water heated by volcanic rock deep within the Earth's crust.

A hydrothermal vent is a geyser on the seafloor. It continuously gushes super-hot, mineral-rich water that supports a diverse community of organisms. Although most of the deep sea is sparsely populated, vent sites teem with a fascinating array of life, from tubeworms taller than you to ghost-white crabs.

Hydrothermal vents were discovered in 1977 in the Pacific Ocean. Since then, they have been found in the Atlantic, Indian, and most recently, the Arctic Ocean. Most occur at an average depth of about 2,100 meters (7,000 ft) in areas of seafloor spreading along the Mid-Ocean Ridge system — the underwater mountain chain that winds around the globe.

How do hydrothermal vents form? In some areas along the Mid-Ocean Ridge, the huge plates that form the Earth's crust are moving apart, causing deep cracks in the ocean floor. Seawater seeps into these openings and is heated by the molten rock, or magma, beneath the crust. As the water heats up, it rises.

When this "hot spring" gushes out into the ocean, its temperature may be as high as 360°C (680°F). Yet this water does not boil because it is under so much pressure from the tremendous weight of the ocean above.

Chimneys top some vents. These smokestacks are formed from dissolved metals that precipitate out (form into particles) when the super-hot vent water meets the surrounding seawater, which is only a few degrees above freezing.

Geologists are intrigued by how rapidly vent chimneys grow — as much as a whopping 30 centimeters (12 in) a day! "Godzilla," a vent chimney in the Pacific off the Oregon coast, reached the height of a 15-story building before it toppled and has since been actively rebuilding. In 2000, University of Washington scientists discovered even taller chimneys, up to 55 meters (180 ft) high in the "Lost City" vent field in the Atlantic Ocean.

There are many other reasons why scientists want to learn more about hydrothermal vents. These underwater 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 who live in darkness, from bacteria to tubeworms, may light the way to the development of new drugs, industrial processes, and other products useful to us all.

To understand Earth's structure, think of a hard-boiled egg. The crust is like the egg's thin shell. The mantle is the egg white, and the core is the yolk. However, the Earth's core is divided into two parts: a liquid outer core and a solid inner core.