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COPYRIGHT 2005 Smithsonian Institution
ON AUGUST 7, 1996, reporters, photographers and television camera operators surged into NASA headquarters in Washington, D.C. The crowd focused not on the row of seated scientists in NASA's auditorium but on a small, clear plastic box on the table in front of them. Inside the box was a velvet pillow, and nestled on it like a crown jewel was a rock--from Mars. The scientists announced that they'd found signs of life inside the meteorite. NASA administrator Daniel Goldin gleefully said it was an "unbelievable" day. He was more accurate than he knew.
The rock, the researchers explained, had formed 4.5 billion years ago on Mars, where it remained until 16 million years ago, when it was launched into space, probably by the impact of an asteroid. The rock wandered the inner solar system until 13,000 years ago, when it fell to Antarctica. It sat on the ice near Allan Hills until 1984, when snowmobiling geologists scooped it up.
Scientists headed by David McKay of the Johnson Space Center in Houston found that the rock, called ALH84001, had a peculiar chemical makeup. It contained a combination of minerals and carbon compounds that on Earth are created by microbes. It also had crystals of magnetic iron oxide, called magnetite, which some bacteria produce. Moreover, McKay presented to the crowd an electron microscope view of the rock showing chains of globules that bore a striking resemblance to chains that some bacteria form on Earth. "We believe that these are indeed microfossils from Mars," McKay said, adding that the evidence wasn't "absolute proof" of past Martian life but rather "pointers in that direction."
Among the last to speak that day was J. William Schopf, a University of California at Los Angeles paleobiologist, who specializes in early Earth fossils. "I'll show you the oldest evidence of life on this planet," Schopf said to the audience, and displayed a slide of a 3.465 billion-year-old fossilized chain of microscopic globules that he had found in Australia. "These are demonstrably fossils," Schopf said, implying that NASA's Martian pictures were not. He closed by quoting the astronomer Carl Sagan: "Extraordinary claims require extraordinary evidence."
Despite Schopf's note of skepticism, the NASA announcement was trumpeted worldwide. "Mars lived, rock shows Meteorite holds evidence of life on another world," said the New York Times. "Fossil from the red planet may prove that we are not alone," declared The Independent of London.
Over the past nine years, scientists have taken Sagan's words very much to heart. They've scrutinized the Martian meteorite (which is now on view at the Smithsonian's National Museum of Natural History), and today few believe that it harbored Martian microbes.
The controversy has prompted scientists to ask how they can know whether some blob, crystal or chemical oddity is a sign of life--even on Earth. A debate has flared up over some of the oldest evidence for life on Earth, including the fossils that Schopf proudly displayed in 1996....
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