Sedimentary rocks in the central part of South America contain ancient mineral grains that must have come from the eastern part of the continent.

Geologist Russell Mapes says this must mean that about 145-65 million years ago, the Amazon flowed east to west.

Mr Mapes will present his findings at a geology meeting in Philadelphia.

The age of rocks on the South American continent differs between east and west.

Rocks as old as 2.5 billion years are found on the eastern side of the continent. Because of continual geological activity in the Andes, on the western side, rocks there are much younger.

Changing landscape

If the Amazon had continuously flowed eastward, as it does now, much younger mineral grains would be found in the sediments, because they would have been washed down from the Andes.

"We didn't see any. All along the basin, the ages of the mineral grains all pointed to very specific locations in central and eastern South America," said Mr Mapes, a graduate student from the University of North Carolina (UNC), US.

He explained that these sediments of eastern origin were washed down from a highland area that formed in the Cretaceous Period, when the South American and African tectonic plates broke away from each other.

That might have tilted the river's flow westward, sending sediment as old as two billion years toward the centre of the continent.

Current course

Afterwards, a relatively low ridge, called the Purus Arch, rose in the middle of the continent, running north and south. This divided the Amazon's flow, so that one half flowed eastward toward the Atlantic and the other westward toward the Andes.

In the late Cretaceous, mineral grains younger than 500 million years old began to fill in the basin between the Andes mountains - in the west - and the arch running down the centre of the continent.

After millions of years of build up, the Amazon river finally broke through these sediments and flowed past the Purus arch and into the eastern side of South America. This established the river's current course.

The new data comes from zircons, a type of mineral grain that can be dated in order to determine the age of the sediment.

Previous research has identified a reverse flow, but only in segments of the river. Mr Mapes and his colleague Drew Coleman from UNC traversed about 80% of the Amazon basin, collecting samples of zircon.

Their data supported the previous findings, and illustrate the continent-wide shift of the river's flow over millions of years.

The results will be presented at the Geological Society of America's annual meeting in Philadelphia, which runs from 22-25 October.

Police at tiny Gundaroo village near Canberra today Wednesday said they were hunting thieves who used crowbars to crack open water tanks and steal the precious contents.

"I came to the tap to get a glass of water and all I got out was mud. I couldn't really believe it had happened," farmer Lindy Hayman said.

In nearby Bungendore, water has been stolen from village dams and tanks, while 50 kilometers away in Yass police have reports of theft from the city's near-dry river.

In the past two weeks, the Government has announced more than $900 million in drought relief as farmers face the driest period for a generation and with the hottest summer months still ahead.

More than 90 per cent of the most populous state of New South Wales is in drought, with many farmers enduring five continuous years of below average rainfall.

The area around Gundaroo and the nearby town of Goulburn have been particularly hard-hit, with Goulburn's main dam having run dry.

Ms Hayman said she and partner Zed Zawalski lost 75,000 litres from their small Gundaroo olive grove and cattle farm while they were out.

Nearby, in the village main street, Kerry Wagstaff said thieves emptied two 30,000-litre water tanks, used to provide water for the house and for their vegetable garden.

"With things the way they are, we are down to asking visiting friends if they really need a shower," Ms Wagstaff said.

Police in the regional Goulburn headquarters said they were investigating several incidents of water theft and advised people to lock their water stores as summer draws closer.

"But I think things are not yet that desperate that it's happening a lot and people need to go round stealing water," Acting Inspector Doug Pilkington said.

But Tuvalu, a speck of nine islands with 10,000 inhabitants, said its predicament was even more urgent as the ocean kept rising and threatening to engulf its palm-fringed homes.

"Our islands are very flat, as flat as a table," Paani Laupepa, a Tuvalu delegate at the Pacific Islands Forum in Fiji, said today.

"It will be the whole population, the entire 10,000 people will be affected. We have a right to live in this environment and now we are being forced away," he said.

Tuvalu is upset that regional heavyweight Australia, a major aid donor but also one of the biggest per capita emitters of the greenhouse gases responsible for global warning, has so far spurned advances to help resettle its people.

It is also angry that Australia, already accused of being a regional bully over a diplomatic spat with the Solomon Islands and Papua New Guinea, was unable to arrange even a short meeting between Prime Minister John Howard and his Tuvaluan counterpart Apisai Ielemia.

"Howard has no commitment. We are very frustrated," Mr Laupepa said.

Kiribati, a nation of 33 coral atolls straddling the Equator and of 105,00 people, is in the same situation.

President Anote Tong said Kiribati had unusually high tides in the past two weeks and feared small, low-lying nations like his would be swamped within 50 years.

"If we are talking about our island states submerging in 10 years' time, we simply have to find somewhere else to go," Mr Tong said.

Kiribati, Tuvalu, the Federated States of Micronesia, the Marshall Islands and parts of Papua New Guinea and Vanuatu are considered at greatest risk.

A climate change report by Australia's leading scientific research body released two weeks ago found that Micronesia had experienced an annual sea level rise of 21.4mm since 2001.

It said a sea level rise of 30-50 cm would affect hundreds of millions of people across the Asia-Pacific region, slashing economic output, inundating large areas of Bangladesh, India and Vietnam and reducing Kiribati, Fiji and the Maldives to a small fraction of their current land area.

It also called on Australia, which is not a signatory to the Kyoto Protocol to cut greenhouse gases, to do more to combat climate change and to be more open to environmental refugees.

Mr Laupepa said the responsibility for taking in those made homeless by rising sea levels rests squarely with the major greenhouse gas emitters.

"We are deeply concerned. Certainly they have a moral obligation to take responsibility for the problems created by their actions," he said.

It wasn't immediately clear what was tainting the section of the Yellow River. Environmental protection officials took samples and were trying to determine whether the sewage was toxic, the official Xinhua news agency said.

"Residents were alarmed to see a sewage pipe pouring red water into the country's second longest river" on Sunday between 3 p.m. and 6 p.m., the agency said.

A news photo from the local paper showed a resident in the city center by a stretch of the river - a drinking water source for millions - that was rose-colored instead of the usual milky brown. Other photos showed patches of bright red and pink.

An official from Yellow River Water Resource Committee in Lanzhou confirmed the pollution. He said they were still analyzing the sample and had not determined what caused it. Like many Chinese officials, he gave only his family name, Wang.

Environmental protection has taken on new urgency for Chinese leaders following a November 2005 chemical spill in the Songhua River in northeastern China which forced the city of Harbin to shut down its water supply for days and sent toxins flowing into Russia.

China's cities are among the world's smoggiest, and the government says its major rivers, canals and lakes are badly polluted by industrial, agricultural and household pollution.

Hundreds of millions of people live without adequate supplies of clean drinking water. Throughout the country, protests have erupted over complaints by farmers that uncontrolled discharges by factories are ruining crops and poisoning water supplies.

Said another: "Let the mayor of Lanzhou drink the water and then they will immediately have measures in place to deal with the environmental pollution."

Kang Mingke, an official with the city's environment protection bureau, said there were no chemical plants located nearby, according to Xinhua. He said the red water could have come from central heating companies who dye their hot water to prevent people from diverting it for their own use, the news agency said.

John Hocevar, an oceans specialist for Greenpeace USA, said that the photos he had seen of the spill might indicate a "red tide," a burst of toxic plankton in the water, spurred by the presence of nutrient-rich waste from the sewage spill.

Alternatively, he said industrial toxins could have caused the red color. "It's too early to say what's exactly in this," he said. "It could be just about anything."

Noting that local government officials have said there is no industry in the area, Hocevar said if the discoloration is the result of industrial waste, it would have to come from illegal dumping.

"For a spill this size to have this kind of effect, it would have to be illegal," he said.