Magazine article Science News

Seafloor Chemistry: Life's Building Blocks Made Inorganically

Magazine article Science News

Seafloor Chemistry: Life's Building Blocks Made Inorganically

Article excerpt

Hydrocarbons in the fluids spewing from a set of hydrothermal vents on the seafloor of the central Atlantic were produced by inorganic chemical reactions within the ocean crust, scientists suggest. The finding holds possibly profound implications for the origins of life.

The Lost City hydrothermal field, which sits on the side of an undersea mountain about 2,500 kilometers east of Bermuda, was discovered in December 2000 (SN: 7/14/01, p. 21). Unlike most hydrothermal vents, which crop up along mid-ocean ridges where tectonic plates spread to form new seafloor, those of the Lost City lie about 15 km west of the Mid-Atlantic Ridge on ocean crust that's about 1.5 million years old. Accordingly, the chemistry of the fluids surging from the Lost City vents differs radically from that found at other hydrothermal sites, says Giora Proskurowski, a geochemist at Woods Hole (Mass.) Oceanographic Institution.

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Most hydrothermal vents spew a highly acidic, mineral-rich broth at temperatures as high as 400[degrees]C. The sulfide minerals that precipitate when those hot fluids mix with near-freezing seawater form dark, crumbly chimneys that typically reach heights of only 20 meters or so before they collapse. At the Lost City site, however, vent fluids are alkaline, have temperatures between 28[degrees]C and 90[degrees]C, and are rich in dissolved carbonates, Proskurowski notes. Because carbonate minerals are much stronger than sulfides, the lofty white chimneys that form in the Lost City can grow at least 60 m tall.

Lost City fluids also contain small quantities of hydrocarbons such as methane, ethane, and butane. A number of clues suggests that those substances, whose natural production usually results from the long-term heating of sediment rich in organic matter, were actually produced by inorganic chemical reactions, Proskurowski says. …

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