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Possibly the oldest object ever found

Ian Sample

The rock that hit Lake Tagish was created before the solar system.

AS LUMPS of rock go it looks much like any other, unexceptional despite the deep red of its cool, smooth surface. The pieces range in size from pea-sized lumps to larger fist-sized chunks. But on Friday, scientists announced this was no ordinary stone. Prised from a frozen lake in northern Canada, it has become a prime candidate for the oldest known object on earth.

The chunk came from a meteorite that scored an arc of fire across the skies before slamming into Lake Tagish in British Columbia in 2000. It has been pored over by scientists ever since, and is now revealed to contain particles that predate the birth of our nearest star, the sun.

The Tagish meteorite was already regarded as exceptional because its mineral composition linked it to the earliest days of the formation of the solar system, more than 4.5 billion years ago. The fragments of meteorite that still exist are among the most pristine in the world, as they were protected from contamination when they became wedged in blocks of lake ice.

The latest research shows that peppered throughout the meteorite are grains that formed even earlier, in a frigid cloud of molecules, possibly at the edge of the swirling disc of dust that ultimately collapsed to form the sun and all the planets of the solar system.

The discovery suggests that while the first light from the sun fell on the fledgling earth, as the dinosaurs rose and died out and humans gained dominance, the meteorite was hurtling around the heavens on a billions-of-years-long journey destined to terminate with a thud in Yukon territory.

Researchers at the National Aeronautics and Space Administration's Johnson Space Centre in Houston examined a 2-gm fragment of the meteorite and focussed on tiny, hollow, carbon spheres embedded within it. Each "globule" measured just a few thousandths of a millimetre across.

Isotope tests

Using electron microscopy and isotope tests, scientists looked at the chemical make-up of the grains and discovered they had unusual ratios of different forms of nitrogen and hydrogen. Ratios of the isotope nitrogen-15 to nitrogen-14 were nearly twice those on earth, while the ratio of deuterium, a heavy form of hydrogen, to normal hydrogen, was between 2.5 and nine times higher than usual.

Fragments of the Tagish meteorite were recovered after locals spotted the fireball it created as it tore through the atmosphere at 20 miles a second. Large clumps of the meteorite were collected from the surface of the frozen lake, but other chunks were removed later embedded in blocks of ice, and transported to research labs.

Around one tonne of fragments from the meteorite are now held in the Natural History Museum in London and at other sites in the U.S., Canada and Germany. — © Guardian Newspapers Limited 2006

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