NARRATOR: When life took hold on the planet around four billion years ago, there was a vast network of hydrothermal vents perhaps providing the geochemical energy to spawn and support life. There is now evidence that the surface of this early Earth was bombarded by meteors and asteroids. The safest harbor for life may have been in the deep—a deep-sea mountain range over 46,000 miles long known as the mid-ocean ridge system. It stretches around the planet like the seams on a baseball and marks where the great plates of the Earth's crust are spreading apart. All along this vast network, volcanic eruptions give birth to new ocean floor. And molten rock, deep under the seabed, creates the scalding black smokers that stream from vents and chimneys. The geology and chemistry of the vents have changed little. Some of these chimneys tower as high as 15-story buildings. And though sunlight never reaches them, they are blanketed with life.

VERONIQUE ROBIGOU, Marine Geologist, University of Washington: It's part of this mystery about this environment is that you go through the really dark water where you don't expect to find much, and then suddenly you start seeing life and it's life that's very beautiful because it is very bright and luminescent and also very striking, because it doesn't look like anything that we're used to.

NARRATOR: These worms harbor inside their bodies a remarkable source of food: tiny, single-celled bacteria. These microbes are able to produce food using hydrogen sulfide and other chemicals that flow around the chimneys. Each microbe is invisible to the naked eye, but when billions clump together, they appear like cottony webs draping the sea floor. As plants at the surface use the energy of light these microbes use energy stored in chemicals to grow and multiply. The larger creatures in this world either live off microbes within their bodies or prey on one another. Giant spider crabs...snails and sea stars...the fish and the octopus—all are ultimately dependent on tiny, single-celled organisms and the volcanic fluids that flow from the rocks. This is a world where the energy for life springs not from the Sun but from the geothermal forces of the Earth itself.

CHUCK FISHER, Biologist, Penn State University: As a biologist, I have no doubt in my mind whatsoever that the geology is the driver for the biology and, in fact, even the structure of the rocks that are in the chimneys are going to determine the type of fauna you find on top of the chimneys. And by delving inside a chimney, they may find clues to how life itself originated.

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