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 w orldwatch n Groundwater tracked via satellite: Scientists at Stanford University in California have developed a technique for accurately monitoring the volume of groundwater in aquifers in agricultural regions using satellite data.
With aquifers around the world rapidly becoming depleted due to the widespread use of groundwater, primarily for irrigation, regulation is vitally important. Levels can fluctuate seasonally due to changing patterns of rainfall, snowmelt and extraction, but regulators can only make direct measurements from wells drilled directly into the aquifers. Such wells are rare, compared to the size of most groundwater systems.
atellite data can be used to measure the movement of the ground above the aquifer as water levels rise and fall, but these data can be rendered inaccurate by the presence of plants, particularly crops, whose heights change on an almost daily basis.
he scientists analysed a decade’s worth of surface-elevation data from the San Luis Valley in Colorado. They produced maps of satellite measurements and found a regular pattern of high- and low-quality data. By overlaying Google Earth images of the farmland, they found that the high-quality data corresponded with dry, crop-free areas. By comparing data from these areas with data collected from local wells, they showed that the satellite results provided an accurate picture of groundwater levels in the aquifers below.
he scientists suggest that this technique can be used in agricultural regions around the world, including areas that lack modern infrastructure such as wells.
Maori fires transformed New Zealand shut terstock
New Zealand’s early settlers used fire to rapidly transform the South Island’s ecosystems, according to new research.
n international team led by Dave McWethy and Cathy Whitlock of Montana State University used pollen records, charcoal fragments and algae and midge remains to reconstruct the environmental history of 16 small lakes. The results indicated that several high-intensity fire events occurred within two centuries of the arrival of Maoris during the 13th century.
Previous research has shown that prior to Maori arrival, closed forest covered 85–90 per cent of New Zealand, but by the mid-19th century, when the first Europeans arrived, grass and shrubs had replaced more than 40 per cent of the South Island’s forests. Archaeological evidence suggests that in the cooler southern areas, the Maori relied on the rhizomes of bracken fern, which replaced the burnt forests.
The team used new records of past climate to disprove the hypothesis that the increase in fire frequency was due to unusual climatic conditions. Before human arrival, forest fires were generally rare, occurring only once every 1,000–2,000 years.
‘What is remarkable is that small mostly subsistence-based groups of people were able to burn large tracts of forests throughout the relatively large South Island in only a few decades,’ McWethy said.
The authors suggest that a better understanding of the history of fire and people in New Zealand will improve the development of strategies for forest-fire management and conservation.
ATLANTIC OCEAN The spread of areas of low oxygen in the Atlantic Ocean is restricting the range of fish such as marlin, forcing them into shallower waters, where they are more likely to be caught, according to new research. Rising ocean temperatures are expected to exacerbate the problem, as they reduce the amount of oxygen dissolved in water.
INDONESIA Six years after the Boxing Day tsunami struck, the German–Indonesian Tsunami Early Warning System for the Indian Ocean has been completed. Comprising 300 stations made up of tide gauges, seismometers, GPS stations and buoys, the system is designed to provide a warning within five minutes of a submarine earthquake taking place.
GLOBAL Tiny larval fish can settle long distances – in some cases more than 150 kilometres – from where they were spawned, according to a new study. The findings give weight to the idea that marine reserves can help to rebuild fish stocks in unprotected areas.
CANARY ISLANDS The establishment of a population of Egyptian vultures on the Canary Islands was apparently made possible by the arrival of humans 2,500 years ago, according to a study by Spanish researchers. Genetic analysis demonstrated that the birds arrived at the same time as the humans, whose livestock would have provided the vultures with a food source.
UK The past decade has been the best for the UK’s rivers since the Industrial Revolution, according to the Environment Agency. Wildlife is returning in record numbers to many rivers, and incidents of serious water pollution have more than halved since 2001.
february 2011 www.geographical.co.uk 11