Aboard Atlantis

Tuesday, September 19, 2006

In the still darkness more than a mile beneath Atlantis' keel, a battle is raging. Pitted against each other, earth's elemental forces - plate techtonics, volcanism, the biological imperative, and the sea. The Atlantis has traveled to the front line of this timeless conflict, the Juan de Fuca Ridge, 135 miles northwest of Astoria, Oregon. Alvin pilots returning from the battlefield recently surfaced with evidence of the conflict.

At first glance, the samples on Min-Hiu Lin's sample table appear ordinary enough. A dozen rough hewn fragments, charcoal black and streaked with a lattice of white marbling. A thermos-sized geode, split in half, burnt to ash and lined with fool's gold. The blackened stump of a stalagmite. Identification tags inscribed with blue ball point pen lay alongside each sample. They say "Finn," "Hot Harold" and "Hulk."

Smelling of brimstone and sulfur, the samples appear unlikely objects of scientific curiosity. In this case, however, appearances are deceiving. In oceanographic circles they are among the most sought after of prizes, trophies still so rare that scientists are willing to descend to depths of the ocean, and hope someday to travel into the depths of space, to obtain them.

Lin, a dimunitive Taiwanese researcher with spiky black hair, said that the Juan de Fuca Ridge is an area known for its tectonic activity. "The Axial Seamount on the Juan de Fuca Ridge has been studied continuously since 1983," she said. It has given scientists an opportunity to study the dynamics of volcanism and tectonism on Juan de Fuca's hydrothermal vents."

On a recent dive, Alvin explored "Faulty Towers," a complex of what scientists call polymetallic sulfide chimneys. Composed of metal, sulfides, mostly, chimneys form along undersea mountain ranges called mid-ocean ridges. Ridges form when tectonic plates collide, or in the case of the Juan de Fuca Ridge, separate. As the plates pull apart, the seafloor spreads. Fissures or cracks form, and magma rises to fill the gap. The magma heats invading seawater to more than 700 degrees F. Hydrostatic pressure at 2,500 meters is two tons per square inch, enough to prevent water from boiling.

The superheated water erodes and mixes with surrounding minerals, forming a fluid rich in metals and sulfides. Pressure pushes the fluid up though the seafloor in hot springs called hydrothermal vents. The hot fluid meets and mixes with the surrounding, cold salty seawater. Metal sulfides in the fluid condense into plumes of black "smoke." Over time, the particle-rich plumes precipitate, forming smokestack-like structures called black smoker "chimneys." The samples on Min-Hiu Lin's table are pieces of three such chimneys - Finn, Hot Harold and Hulk.

Over the years many chimneys have been identified along the Juan de Fuca Ridge, part of the Ring of Fire. Roane, Giraffe, Mothra, Salty Dawg, Sasquatch, Sully. Giraffe is 22 meters tall. Barren in 2000, Sully now sports a luxuriant carpet of 2-meter-long tubeworms. In 1977 when hydrothermal vents were first observed near the Galapagos Islands, scientists first documented the existance of giant tube worms. Some grow to 10 feet in length, and bright red blood - iron-rich hemoglobin - courses though their bodies.

In the decades since their discovery, scientists have sought an answer to a fundamental question: How can tubeworms and the other denizens of the hydrothermal vent community - giant clams, worms, shrimp, and bacteria that survive on sulfur - exist at the bottom of the ocean, in darkness, in freezing tempertures and under crushing pressures, close to energetic plumes of superheated fluid saturated with lethal amounts of methane, manganese and iron?

To answer that question, Dr. Jeffery Cramer, a scientist from the University of Washington, studies heat-loving bacteria called thermophiles. "Thermophiles are representations of earth's earliest life forms," he said. Though they have evolved over the eons, he said, compairing contemporay thermophiles to Formula One racing cars, and their primordial ancestors to horse and buggy, "some scientists believe that life on this planet began billions of years ago in
hydrothermal vents just like the ones we see now, and that every organism on earth - including us - evolved from thermophilic bacteria."

Thermophiles live inside hydrothermal vents. They line the narrow chambers and arteries of sulfur chimneys, clinging to deposits of pyrite - fool's gold - coating relatively cool passages filled with a sand-like mineral. Unlike plants, which anchor a food chain based on photosynthesis, thermophiles are chemosynthetic. They derive their sustenance from the chemicals spewing from the vents. Able to tolerate temperatures of 212 degrees F, they eat sulfur and exhale ferrous iron. Oxygen poisons them.

Thermophiles also thrive inside the bodies of tubeworms like those living on Sully. Tubeworms have a specialized organ that contains billions of thermophillic bacteria. From the sulfur they absorb, the bacteria generate organic material that nourishes the host worm. The worms have no need for a mouth or digestive tract, which they lack. This symbiosis between organisms and bacteria extends to the clams, shrimp and other chemosynthetic organisms living near the vents.

The existance of such a specialized ecosystem has raised other questions. If life on earth arose from chemosynthetic bacteria living in hot springs billions of years ago, where did the bacteria come from? Comets or asteroids? Perhaps, said Cramer, although he cautioned the answer may never be answered irrefutably. Besides hydrothermal vents, thermophile-like microbes called extremophiles have been discovered living in the beds of dried alkaline lakes, under glaciers, and in methane seeps. Some thrive in radiation that would quickly kill any other organism. Others eat hydrocarbons - oil. Because of their tenaciousness, "it's possible that some extremophile may be able to survive in the freezing vacuume of space also," said Cramer.

Could thermophilic bacteria exist elsewhere? Scientists speculate that the moons of Jupiter, particularly Europa, may contain two ingredients that vastly increase the possibilty of life - volcanism and liquid water. The Hubble space telescope has observed volcanic eruptions on Europa, and under Europa's icy crust liquid oceans may flow. Nasa has proposed sending a probe to Europa. It may be equipped with a radioactive heat source that would melt through the ice and descend into the ocean below. The probe would seek out heat sources like hydrothermal vents.

"There's a very real possibilty that Europa could sustain chemosynthetic life similar to our terrestrial versions," said Cramer. "If it does, then life may be much more common than we thought."


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