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‘The real time machine’
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 last week, scientists announced that it 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 has been revealed to contain particles that predate the birth of our nearest star, the sun.
The Tagish Lake 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 4.5bn 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 Nasa’s Johnson Space Centre in Houston examined a two gram fragment of the meteorite and focused on tiny, hollow, carbon spheres embedded within it. Each “globule” measured just a few thousandths of a millimetre across.
Using electron microscopy and isotope tests, the 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.
Reporting in the journal Science, a team lead by Keiko Nakamura-Messenger and Michael Zolensky show the levels of the isotopes in the meteorite could only arise from chemical reactions taking place in an extremely cold climate, where temperatures were as low as -260C. Those conditions would only be found in remote molecular clouds before the formation of the solar system, or at the very edge of what is known as the protosolar disc that was later to coalesce into the celestial bodies of the solar system.
“These little particles within the meteorite seem to predate everything else. We don’t know exactly how old they are, but they could be billions of years older than the rest of the meteorite,” said Dr Zolensky.
Hydroelectric power plants — hailed as providers of clean energy — could be dangerous contributors to climate change. This is the startling claim of scientists who say that the dams the plants use produce large amounts of methane, one of the most potent causes of global warming.
At a meeting of Unesco in Paris recently, scientists from France and Brazil presented evidence to show that organic matter is often trapped in reservoirs when dams are built. This matter then decays with the result that the water emits carbon dioxide and — more importantly — methane, a gas that has 20 times the warming impact of carbon dioxide.
This problem is particularly severe in the tropics, add the scientists, who include Philip Fearnside, of the National Institute for Research in the Amazon, in Manaus. He argued in Nature magazine that a typical hydroelectric power station will, during the first 10 years of its life, produce four times the amount of carbon that a comparable fossil-fuel plant would emit.
Other scientists dispute these figures, however. They say that the emission of methane only occurs for the first few years of a dam’s operation and that hydroelectric plants settle down to produce relatively modest amounts of methane and carbon dioxide.
Songbirds change their tune when they move to cities, according to new research. Scientists found that great tits adapted to urban living by singing faster, shorter songs that were at a higher frequency than their forest-dwelling cousins.
Rapid urbanisation around the world and the subsequent increase in ambient noise has proven problematic for animals which use sound to communicate. For birds in particular, city noises can mask the exchange of vital information and prevent males from attracting mates.
To see how birds reacted to increased noise, Hans Slabbekoorn of Leiden University recorded the songs of great tits in 10 European cities including London, Prague, Paris and Amsterdam. He then compared the songs with birds of the same species in nearby forests. The results, published in the journal Current Biology, showed that songs important in attracting mates and defending territory were markedly different in the urban setting.
“The songs diverged in several parameters,” said Dr Slabbekoorn. “In 10 out of 10 comparisons we found that birds in cities use a higher minimum frequency. The songs in cities are faster, especially the duration of the first element of each of those repetitive song phrases.”
He explained the change as a response to increased low frequencies in cities, such as traffic noise. Great tits use a wide range of frequencies, allowing them to tailor their songs to their environments. In addition, they can pick up new songs from neighbours when moving to a new environment.
The study will give conservationists better information on why urban areas tend to have the same types of bird. “Sound is not the only part of the changes when a city expands — vegetation and food availability may not be sufficient for many species,” said Dr Slabbekoorn.
“But species that may otherwise be likely to breed in urban areas may be pushed out finally by increased noise interference.” The changes in song could mark the first step in an evolutionary process called speciation — when an organism splits into two or more different species because of the differing environmental pressures facing different populations.
Dr Slabbekoorn said that speciation would be possible for the great tits but, because it would take many generations for the evolution to occur, it was difficult to predict whether the birds were already on this path. — Dawn/The Guardian News Service
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