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Year In Science

Jan 13, 2002 6:00 AMNov 12, 2019 6:02 AM


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Priceless ZirconIn a jewelry store, a zircon can pass as a cheap diamond. But a speck of zircon found in the Australian outback is proving priceless to geologists. In January, a team of researchers reported that this crystal was dated as Earth's oldest known rock—at around 4.4 billion years old. Although no bigger than a grain of sand, it contains valuable clues to when and how our planet took shape. Many geologists used to believe that Earth was a roiling mass of molten rock for the first 300 million years of its existence. But the zircon found by Simon Wilde, a geologist at the Curtin University of Technology in Perth, was formed just 160 million years after Earth itself. If the crystal could form so early in Earth's history, the planet's surface must have cooled and hardened considerably faster than researchers had suspected. The oxygen within the zircon tells an even more remarkable tale. The ratio of oxygen-18, a rare isotope, to ordinary oxygen-16, was considerably higher in the stone than the ratio found in Earth's mantle. The disparity is a clue that the zircon formed within rock that had interacted with water on Earth's surface. And that would mean the oceans formed earlier than had ever been suspected—more than 4 billion years ago. The finding also suggests that life, which began in the oceans, may have evolved far earlier than previously guessed. "It's amazing how one little speck of crystal can change everything," says Wilde. — Curtis Rist

Let Them Eat GlassBeneath the ocean floor, a quarter mile into Earth's crust, bacteria are hard at work feeding on volcanic glass and freeing trapped trace elements. Scientists had no idea that the process, called bioalteration, was so widespread until this year, when research showed that the microbes might be found in as much as 90 percent of the volcanic glass that is within 1,000 feet of the seafloor. Hubert Staudigel, a geologist at the Scripps Institution of Oceanography, calls the microbes the "rock bottom of the food chain" and notes that their ubiquity means that the biosphere is much deeper than scientists thought. "It goes deep into the oceanic crust and covers half the planet," Staudigel says. He and his colleagues even found tiny wormlike tracks as far down as 1,650 feet. Staudigel says the microbes have implications for extraterrestrial life: By defining the niches in which life exists on Earth, researchers can look for similar traces of life on other planets. Martin Fisk, a marine geologist at Oregon State University, says he's so certain he can identify the tracks of the microbes that he asked NASA to bring him back a piece of pillow basalt—a type of glassy lava—from Mars. "If you can bring back a piece of pillow basalt," he says, "I can tell you if there was ever life on Mars. Once those microbes make holes in rocks, they're permanent." — Lauren Gravitz

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