Life where you least expect it.

• Author: Braffman-Miller, Judith
• Position: Science & Technology - Habitability in exoplanets

IN 1977, SCIENTIFIC researchers aboard a submarine dubbed Alvin descended down to the seafloor, where they observed a hydrothermal vent located off the Galapagos Islands. What they saw shocked them. Hydrothermal vents are fissures situated at the ocean bottom, which spit scalding, acidic water out into the surrounding sea. Looking out through the sub's tiny windows, the amazed alien visitors saw thickets of tube worms--some as tall as four feet high--waving in the ocean currents like crimson tulips in the winds of March.

Hydrothermal vents form where Earth's crustal plates gradually are spreading apart Hot magma is seeping up from below to create mountain ranges termed midocean ridges. As cracks develop where this spreading occurs, the seawater sinks a mile or two down into the hot rock below. Now, enriched with precious minerals obtained from the hot rock, the scalding hot water rises to the ocean floor to create a vent.

In addition to the tube worms, which so far have been seen only in the Pacific, there are other denizens of the vents. For instance, there are small benthic worms that frolic through the mud, as well as pencil-thin Jericho worms sporting accordion-like tubes. There also are finger-length crimson palm-worms that stand upright, displaying red leg-like structures on their heads. A unique class of tiny worms termed Alvinellids--named in honor of the sub that discovered them--dwell on the walls of mineral deposits that form near the vents. Crabs, mussels, clams, and shrimp also inhabit the vents in huge numbers--but they are not the same species that we are familiar with. For example, the tiny shrimp that reside around the vents in the mid-Atlantic have no eyes.

Scientists are uncertain about how such shrimp and other creatures are able to thrive in the chemical-rich seawater that would kill ordinary shellfish. Indeed, biologists have observed a rich variety of crustaceans hanging around vents, including amphipods resembling sand fleas, and tiny lobsters called galatheids.

Bacteria also inhabit this environment. They are the first living tidbits to colonize newly formed vents, arriving in a snowy blast, and then floating down to create white sheets glued to the seafloor. Bacteria have been discovered underneath the ocean's floor as well. It seems likely that they emerge from beneath when the opportunity presents itself. Vent bacteria can endure much higher temperatures than any other known organism. Creatures such as the tube...