Vulcan Octopus  © Rod Mickens / AMNH

Virtually every day, a new hydrothermal vent springs up somewhere on the ocean floor. Some emit jets of hot, clear fluid; others spout water black with minerals. The animals found at these vents are more than merely odd—they are truly bizarre. Before their discovery in 1977, their very existence was considered impossible. Deriving no energy from the Sun, they survive on chemicals that would be toxic to most other animals on Earth.

Fountains of Life
In 1977, two geologists descended 2.5 kilometers (8,200 feet) into the ocean near the Galapagos Islands and discovered jets of hot water gushing from rifts in the sea floor. To their amazement, they found that these deep-sea vents were home to bizarre life-forms so foreign they changed the way we think about life on Earth, its origins—and the possibility of life on other planets.

What's so special about deep-sea vent animals?

Life Without Sunlight
Before hydrothermal, or hot-water, vents were discovered, most life on Earth was thought to depend on energy from the Sun. But there is no sunlight on the deep sea floor—so where do vent animals get their energy?

All land and ocean plants, algae and some bacteria use the Sun's energy to make sugars and other nutrients. This process, called photosynthesis, provides food for most life on Earth. The energy that animals get from eating plants - or from eating animals that eat plants—is really stored solar energy.

The food chain at hydrothermal vents, however, is not based on photosynthesis. Here, specially adapted bacteria produce sugars and other nutrients using energy from chemicals, not sunlight—a process called chemosynthesis. These bacteria provide energy for the entire community of vent animals.

Cold seeps provide a stable, steady flow of chemicals, enabling animals to live much longer than those at hot vents—perhaps even for centuries. © Woods Hole Oceanographic Institution

Here, specially adapted bacteria consume chemical nutrients such as methane, sulfides and petroleum that flow from the ground. These bacteria in turn feed vast fields of tube worms and mussels.

The dark lines on Jupiter's moon Europa show where water may have seeped up through cracks in the ice. The presence of an ocean beneath the ice could mean that Europa has the necessary conditions for life. Photo: NASA / JPL Galileo

The Origin of Life?
The discovery of animals that live without sunlight has changed the way scientists look at the origin of life on Earth—and possibly on other planets as well.

Billions of years ago, Earth was bombarded by cosmic rays that would have made life on its surface nearly impossible. But since we now know that abundant life can flourish without sunlight, it seems possible that the first life on Earth may have originated on the deep sea floor. There could even be life elsewhere in the universe—at hydrothermal vents on the sea floor of Jupiter's moon Europa, for example, or in warm, wet places beneath the surface of Mars.