The Year in Science: Geology

Sunday, January 08, 2006

Photosynthesizing Life-Form Exists Without Sunlight

Long confined to sun-loving, surface-dwelling organisms, the process of photosynthesis went underwater this year—7,843 feet under.

J. Thomas Beatty, a microbiologist at the University of British Columbia, and a team of researchers found a new type of bacteria off the coast of Central America. They are the first known organisms to derive energy by photosynthesis while living in an environment naturally devoid of sunlight.

Beatty believes that when 570 degree Fahrenheit water from thermal vents hits cold, deep ocean currents, several light-producing processes may occur: sonoluminescence from imploding gas bubbles; chemiluminescence from chemical reactions (analogous to fireflies lighting up); crystalloluminescence from the formation of crystal bonds; and triboluminescence from the breaking of those bonds. Nonetheless, the light emitted is so slight that very few bacteria can grow. "There are fewer than two cells for every milliliter," says Beatty. That's proportionally less than a single grain of sugar in a cup of coffee.

Even so, the organisms are important. Before the development of photosynthesis, which creates oxygen, Earth's surface was bombarded by ultraviolet radiation and was relatively inhospitable to life. This led researchers to argue that photosynthesis—and early life—evolved around hydrothermal vents on the ocean floor, safe from surface radiation. Beatty's bacteria may help support that hypothesis.

The discovery may also shed light on how life could evolve on other planets, including Jupiter's moon Europa. Suggestions of hydrothermal activity on Europa led researchers to speculate that life there could resemble ecosystems around hydrothermal vents on Earth and would survive on chemosynthesis, extracting energy from chemicals. "We're saying, 'Well, not so fast,' " Beatty says. "Maybe there's a small component of photosynthesis to this ecosystem."  —Anne Sasso

Student Shakes Up Tectonic Theory

The discovery of a sharp boundary between Earth's hardened outer shell and a softer layer underneath could force a reassessment of how and why tectonic plates move.

Because geologists haven't traveled into the planet to see what's there, they rely on seismic waves to explore Earth's inner layers. The uppermost layer—the lithosphere, divided into tectonic plates—is a rind of cool, rigid rock some 200 miles thick that slides slowly across the surface of the asthenosphere, the warmer, weaker roughly 100-mile-thick layer below. Where the lithosphere stops and the asthenosphere begins has long been defined by temperature: about 2300 degrees Fahrenheit. But in July, Catherine Rychert, a Brown University geology graduate student, reported something no one else had seen: a well-defined lithosphere-asthenosphere boundary that was impossible to explain by temperature change alone.

Previous seismic studies indicated that the rigid lithosphere slowly gave way to the more plastic asthenosphere over the space of 25 miles or more. The new data—based on high-frequency seismic waves—indicate this transition takes place rapidly—within 7 miles. Rychert and her adviser, Karen Fischer, suggest that small amounts of water or pockets of melted rock in the uppermost asthenosphere account for the change in seismic behavior and the abrupt shift between the two layers.

The presence of water and melt challenges geologists' long-held assumption that asthenospheric convection moves tectonic plates around. Instead, the new finding adds evidence that gravity pulling the plates into subduction zones may drag them across the globe. The next step is to expand Rychert's study, which was confined to eastern North America. "If we see it everywhere, strong and sharp, that tells us that something like water and melt is required everywhere," says Fischer. "If we don't, then it will give us a constraint on how these properties might vary." —Anne Sasso

Earth's Inner Core Speedier Than Outer Shell

Earth's inner core is a solid iron ball slightly smaller than the moon. Little is known about it, but geophysicists confirmed this year that it spins—faster than the solid layers of earth surrounding it.

Geophysicist Xiaodong Song of the University of Illinois at Urbana-Champaign and his colleagues studied seismic waves from doublets—pairs of earthquakes from the same place but occurring at different times. If the inner core was spinning faster, scientists reasoned, seismic waves from doublets would move through the core at different speeds as a result of the inconsistent makeup of the core's iron crystals.

Song calculates that the solid inner core spins just slightly faster per year than the rest of the planet, a difference that adds up to an extra revolution every 1,000 years or so. His discovery could help explain how the inner core interacts with convection in the outer core to drive Earth's magnetic field. The field shields us from bombardment by charged particles from the sun.

"We have only a 30- to 40-year snapshot," cautions Song. The data his team uses first became available in the 1960s, when a worldwide seismographic network was established. What happened before that is unknown. Song expects more breakthroughs in the coming years—as long as Earth keeps quaking.  —Anne Sasso

Japanese Measure Earth's Nuclear Core

Thirty-two hundred feet below the summit of Mount Ikeno in central Japan, workers flicked on the switch at the first neutrino detector sensitive enough to pick up geoneutrinos emanating from Earth's interior.

The detector is already offering insight into our planet's core. Neutrinos are quantum particles that interact with matter so weakly that billions pass unaffected through our bodies every second. By tracking geoneutrinos produced by the decay of uranium-238 and thorium-232 in Earth's interior, the detector, called Kamland, has provided the first direct measurement of the amount of terrestrial heat caused by radioactivity. About half the heat produced by Earth is thought to come from internal nuclear reactions, the other half from heat left over from Earth's earliest days as a red-hot planet. In July the project estimated terrestrial radioactivity at less than 60 terawatts at any given time.

The detector, which will also track neutrinos from the sun and beyond, is located in a zinc mine to avoid contamination from cosmic-ray particles. The central element of the experimental apparatus is a 43-foot-wide transparent nylon balloon filled with a 1,000-ton mixture of baby oil, benzene, and a fluorescent material that traces captured neutrinos. The balloon is immersed in a bath of inert oil to prevent interference from background radiation. All of that, in turn, is surrounded by 1,879 photomultiplier tubes, which pick up flashes of light produced as antineutrinos collide with protons in the liquid-filled balloon. On average, the contraption detects one geoneutrino a month.

Atsuto Suzuki, director of the Research Center for Neutrino Science at Tohoku University in Japan, says that the Kamland experiments are the first to directly measure Earth's interior. Building more geoneutrino detectors would permit scientists to develop a detailed picture of the planet's internal activity, but at $30 million each, the cost would be enormous. Even alone, Kamland promises to help solve long-standing questions about plate tectonics and geodynamics. By measuring the amount of radioactive elements inside Earth, the detector can study how the planet formed. It could even be used to examine the interior of the sun. "We have pioneered a new field of research," Suzuki says proudly. "Neutrino geoscience."  —Tony McNicol 

New Computers Uncover Old Quakes on the Moon

Three decades after NASA pulled the plug on a network of sensitive seismometers left on the lunar surface by Apollo astronauts, scientists have taken a second look at their old research and discovered the moon was doing a lot more shaking than they realized at the time.

Throughout the 1970s, the seismometers radioed back data to the lab of University of Texas geophysicist Yosio Nakamura, but his primitive computer's 64 kilobytes of memory were insufficient to process the information. As a result, he was unable to determine the sources for more than 9,000 of the 12,500 disturbances that showed up on the seismographs. So Nakamura and his colleagues reanalyzed all the data this year and reported that 5,885 of the mysterious seismic events turned out to be deep quakes caused by fractures running roughly halfway to the center of the moon. They also reported locating 250 new nests, or regions where the moon's interior seems to fracture repeatedly.

For unclear reasons, deep moonquakes seem largely confined to the side of the moon facing Earth. "Either very few quakes occur on the far side, or there's something at the middle of the moon, possibly molten, that's attenuating the seismic signals," Nakamura says. He has proposed installing more seismometers on the far side of the moon to investigate further, but he will have a long wait. NASA isn't planning another lunar mission until 2010.—Elizabeth Svoboda

New Volcano Rises From Old Volcano

The setting would be perfect for an underwater chapter of the Indiana Jones saga: A 1,000-foot-tall underwater volcano swathed in yellow fluff and patrolled by a swarm of deep-sea eels. The young cone was discovered in March, rising from the bowels of another volcano 30 miles east of American Samoa. Scientists named it Nafanua, after the Samoan goddess of war.

Geologist Hubert Staudigel of the Scripps Institution of Oceanography and geochemist Stan Hart of the Woods Hole Oceanographic Institution discovered the parent volcano, Vailulu'u, in 1999 while searching for the source of a tectonic hot spot. Over the next two years, they returned twice to the underwater terrain—a giant crater two miles across—and studied its seismic and hydrothermal activities.

Then in March, a team of deep-sea scientists led by Craig Young of the University of Oregon and Adele Pile of the University of Sydney returned with a submersible to look for life. Before they descended, their sonar revealed a new feature in Vailulu'u's massive crater, a volcano—Nafanua—that was absent four years earlier. The young volcano is rising about eight inches per day and could breach the surface within a decade.

The submersible crew landed on Nafanua's summit, about 2,000 feet below the surface, and looked out on a teeming landscape. Sulfur-colored mats of microbial life blanketed porous tubes of new lava. Hundreds, perhaps thousands, of foot-long purple-gray eels snaked in every crack and crevice, prompting researchers to nickname Nafanua "Eel City."

Finding the eels (Dysommina rugosa, a species known from Atlantic and Pacific fishing trawls) in such numbers is startling, Young says, because deep-sea eels are normally solitary. Their abundant presence on this peak may be tied to the liquid carbon dioxide spewed by the volcano's hydrothermal vents, which kills virtually all life in the deeper reaches of the crater.

"My hunch is that currents going by contain all kinds of life, including bright red shrimp, the eels' main food source," Staudigel says. "The eels can live inside the plume, but everyone else either dies or is stunned—it's easy pickings." —Megan Mansell Williams

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