w orldwatch n Ancient raindrops reveal mountain growth: A team of researchers has used the residue from ancient raindrops to provide evidence that a wave of mountain building moved down western North America from British Columbia to Mexico between 49 and 27 million years ago. The evidence helps put to rest the idea that the western USA once hosted a high, Tibet-like plateau that eroded to form the mountain ranges seen today.
he researchers analysed the ratios of hydrogen and oxygen isotopes in 2,800 rock samples collected from mountains in western North America in order to calculate the composition of ancient rain that fell on the rocks. Water containing heavier isotopes tends to fall first as a cloud rises, so by measuring the ratio of heavy to light isotopes, it’s possible to infer the elevation of the land on which the rain fell. The elevation trends revealed in the data could then be used to create a history of the entire range.
‘Where we got a huge jump in isotopic ratios, we interpret that as a big uplift,’ said Hari Mix of Stanford University in California.
‘We saw a major isotopic shift at around 49 million years ago, in southwest Montana,’ Mix said. ‘And another one at 39 million years ago, in northern Nevada,’ as the uplift moved southward. It’s generally believed that the uplift was caused when the Farallon plate peeled away from the underside of the continent as it was forced under the North American plate.
nvironment limits species diversity
Species diversification is limited by local environmental factors, according to new research on lizards in the Caribbean. The new findings support and extend the theory of island biogeography developed by Robert MacArthur and EO Wilson during the 1960s. While the idea that factors such as space, food supplies and competition cause species numbers to reach an equilibrium has been around for some time, some recent work has suggested that diversity continues to rise indefinitely. In order to determine which of these competing theories was correct, Daniel Rabosky of the University of California, Berkeley and Richard Glor of the University of Rochester studied patterns of accumulation of lizards over millions of years on the Caribbean islands of Puerto Rico, Jamaica, Hispaniola and Cuba.
Using molecular methods, the pair were able to reconstruct evolutionary trees for the lizard communities on the different islands that showed the relationships among the species. They found that species diversification on the four islands reached a plateau millions of years ago and essentially came to an end.
he results extend the work of MacArthur and Wilson, who developed the theory of island biogeography in order to explain patterns of diversity and richness over ecological timescales, which encompass thousands of years. Rabosky and Glor’s study shows that the same principles hold over millions of years.
n Phone records support regional boundaries: An analysis of 12 billion anonymised phone records, representing 95 per cent of Great Britain’s residential and business landlines, has allowed an international team of researchers to map the nation’s human interactions, based on the amount of information they exchanged.
y mining one of the world’s largest databases of telecommunications records, researchers from MIT, Cornell University and University College London divided Great Britain into regions with strong internal information connections but weaker connections to adjacent regions. For the most part, the results mirrored the existing administrative regions, but there were a number of notable exceptions. For example, some parts of Wales had much stronger connections to cities in western England than they did to the rest of Wales, suggesting that in some ways, the historical distinction between England and Wales may be obsolete.
‘The difference between Scotland and Wales is striking,’ said Carlo Ratti, director of MIT’s Senseable City Lab and lead author of the research. ‘Based on our landline data, Scotland is very separated from the rest of Great Britain: just 23.3 per cent of all call time placed or received there goes to or comes from another part of the country. Conversely, Wales, in spite of its unique cultural and linguistic heritage, is well integrated with its English neighbours to the east.’
he research also identified a new region just west of London centred on high-tech activities.
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10 www.geographical.co.uk February 2011