Some Things New Under the Sea

New microbe species discovered

In the quest to explore the remarkable diversity of microbial life on Earth, a German-American team of scientists has discovered seafloor bacteria that can “eat” natural gases such as ethane, propane, and butane—and in a previously unknown way: without oxygen. The bacteria (left) use sulfate instead of oxygen to metabolize natural gases into energy and organic matter, said WHOI biologist Stefan Sievert, co-author of a study published Oct. 18, 2007, in the journal Nature. The bacteria may have played a role in the evolution of life on early Earth, when oxygen was sparse in the oceans and seafloor hydrothermal vents spewing hydrocarbons were much more common than today (see article below). These microbes also have unusual and still-unknown enzymes that can break down hydrocarbons without heat and oxygen, offering potentially useful catalysts to synthesize compounds, Sievert said. The team also included scientists from the Max Planck Institute for Marine Microbiology, GeoForschungsZentrum, the University of Hamburg, and RWTH Aachen University, all in Germany, and the University of Georgia. See: “Microbes That ‘Eat’ Natural Gas.”

Evidence for undersea origins of life

Scientists have discovered that hydrocarbons—essential building blocks of life—are naturally generated at the bottom of the ocean. The researchers examined rocks from a seafloor hydrothermal vent field called “Lost City” (left)—near the summit of the Atlantis Massif, a curious dome made of rock usually found deep in Earth’s mantle (see article below). Chemical analyses showed that the carbon in the rocks was not formed from atmospheric carbon dioxide, nor made by microbes. Instead, the hydrocarbons were generated by the simple interaction of seawater with mantle rocks—conditions that were likely common during Earth’s early years. The finding bolsters arguments that life on Earth could have originated at seafloor vents, according to geochemist Giora Proskurowski of Woods Hole Oceanographic Institution and Deborah Kelley of the University of Washington, lead authors of a paper published Feb. 1, 2008, in the journal Science. “The generation of hydrocarbons was the very first step; otherwise Earth would have remained lifeless,” said Proskurowski, who conducted the research while earning his doctorate at UW and during postdoctoral work at WHOI. See: “Lost City Pumps Life-essential Chemicals at Rates Unseen at Typical Black Smokers.” (Photo courtesy of D. Kelly and M. Elend (University of Washington), Institute for Exploration, URI-IAO, NOAA, and Lost City Science Team)

Old rock woven into new seafloor crust

A quirky seafloor feature, once considered rare, may instead be rather common and play a key role in shaping Earth’s surface. Scientists had found an intriguing dome on the seafloor, called the Atlantis Massif (left), made of gabbro and peridotite, rocks usually found deep in Earth’s crust and upper mantle layer. The rocks lay near a large “detachment” fault slanting deep into the ocean crust. The researchers now theorize that over hundreds of thousands of years, as Earth’s tectonic plates pulled apart, a mammoth block of upper mantle rock was pulled up along the fault toward the surface and eventually rolled over on the seafloor. The exhumed dome of old rock from the lower crust and upper mantle, called a core complex, was effectively woven into the fabric of “new” ocean crust. Once they knew to look for core complexes, the scientists subsequently found that core complexes covered as much as 40 percent of the seafloor on the flanks of the equatorial Mid-Atlantic Ridge. The discovery has sparked widespread attention since it was first reported July 26, 2006, in Nature by geophysicist Deborah Smith of Woods Hole Oceanographic Institution, Johnson Cann of the University of Leeds (UK), and Javier Escartín of the National Center for Scientific Research (France).  See: “New Wrinkles in the Fabric of the Seafloor.” (Image courtesy of University of Washington for the Lost City Program by the Center for Environmental Visualization)

What triggers continental rifting?

Rifting—the process that ruptures continents and forms new ocean basins between them—is a fundamental phenomenon that has shaped the face of the Earth, yet scientists continue to find unexpected subtleties in what controls how continents rift. To learn what caused Baja California to separate from the mainland and form the small intervening sea, researchers led by WHOI geophysicist Daniel Lizarralde deployed closely spaced seismometers in and around the Gulf of California, where rifting is rupturing continental crust and creating new ocean crust that is spreading outward. According to theory, hot temperatures in the mantle trigger rifting by causing hot, buoyant magma to rise, but this would occur uniformly over large areas. The Gulf of California seismic array recorded seismic waves traveling through Earth’s crust, unveiling highly detailed images of crustal structure (left) and revealing that rifting occurs in different ways in different places not far from each other. To explain these variations in rifting “styles,” as the researchers put it, they suggested a novel theory: In an era before rifting began, neighboring continental plates were colliding, forcing crustal material down into the mantle differentially in various places. That created pockets in the mantle with different compositions, making some areas more “fertile” for melting and rifting than others. The research was published July 26, 2007, in Nature. View the Nature article: “Variation in styles of rifting in the Gulf of California” (subscription only).

Funding for all the research above came from the National Science Foundation. The Lost City expedition also received funding from the National Oceanic and Atmospheric Administration.