Until now, it has been accepted generally that the Chicxulub impact off the coast of Mexico 65 million years ago wiped out the dinosaurs. Evidence of the crater left by the giant asteroid or comet has been found under the sea off the coast of Yucatan.

But a group of scientists led by Professor Gerta Keller of Princeton and Professor Wolfgang Stinnesbeck of the University of Karlsruhe begged to differ. They uncovered a series of geological clues which suggests the truth may be far more complicated.

In short, they say that the crater in the Yucatan is too old to have killed off the dinosaurs. Yucatan took the rap for a dino murder that occurred much later.

However, no-one has yet found the crater from the 'real culprit' impact which ended the Age of Reptiles and caused one of the largest mass extinctions in history.

'There is some evidence that it may have hit in India,' says Dr. Keller. The crater, named Shiva by one expert, is estimated to measure 500 kilometres (over 300 miles) in diameter. However, at this time there is little proof of its existence.

Keller says marine microfossils in sediments drilled from the ocean floor show that Chicxulub hit Earth 300,000 years before the mass extinction it was supposed to have caused.

The small marine animals that produced the microfossils escaped virtually unscathed.

The Chicxulub impact conspired with the Deccan Flood Basalt eruptions in India, a period of prolonged and intense volcanic activity, to nudge species towards the brink, said Dr Keller.

Vast amounts of greenhouse gas were pumped into the atmosphere by the Deccan volcanism over a period of more than a million years. By the time Chicxulub struck, land temperatures were seven to eight degrees Celsius warmer than they had been 20,000 earlier.

Weakened by these events, species were finally killed off by the second impact.

The previous impact theory was beautifully simple and appealing. Much of its evidence was drawn from a thin layer of rock known as the 'KT boundary.' This layer is 65 million years old (which is around the time when the dinosaurs disappeared) and is found around the world exposed in cliffs and mines.

For supporters of the impact theory, the KT boundary layers contained two crucial clues. In 1979, scientists discovered that there were high concentrations of a rare element called iridium, which they thought could only have come from an asteroid. Right underneath the iridium was a layer of spherules, tiny balls of rock which seemed to have been condensed from rock which had been vapourised by a massive impact.

But Keller's team concentrated on a series of rock formations in Mexico where the iridium layer was separated from the spherule layer by many metres of sandstone. Keller found evidence such as ancient worm burrows that suggested that the deposition of the sandstone had been interrupted many times.

Her team concluded that there was a gap of some 300,000 years between the deposition of the spherules (from the Chicxulub crater) and the iridium (from an asteroid). Therefore, there must have been two impacts.

Earlier this year the charity commissioned livestock specialist Dr David Kimenye to examine how the herders are coping with the recent drought, uncovering a disastrous story. Over two months, Dr Kimenye talked to pastoralists in five areas across the Mandera district, home to 1.5 million people.

The study discovered that:

- Incidence of drought has increased fourfold in the Mandera region in the past 25 years.

- One-third of herders living there - around half a million people - have already been forced to abandon their pastoral way of life because of adverse climatic conditions.

- During the last drought, so many cattle, camels and goats were lost that 60 per cent of the families who remain as herders need outside assistance to recover. Their surviving herds are too small to support them.

The new findings follow recent warnings from the UK Met Office that if current trends continue one-third of the planet will be desert by the end of 2100. The scientists modelled how drought is likely to increase globally during the coming century because of predicted changes in rainfall and temperature around the world.

At present, according to their calculations, 25 per cent of the Earth's surface is susceptible to moderate drought, rising to 50 per cent by 2100. In addition, the areas susceptible to severe drought - 8 per cent - are expected to rise to 40 per cent. And the figure for extreme drought, currently 3 per cent, will rise to 30 per cent.

And what is doubly worrying about Kimenye's research is that it has revealed that a system of nomadic pastoralism that has, over the centuries, been able to cope with unpredictable weather patterns and regular drought has been brought by climate change to the point of utter extinction.

It is a fact not lost on those who have been forced out of their historic lifestyle to settle at the Quimbiso settlement. Nearby is a stinking pit where the bones of the last of once thriving herds were dumped and burned - victims of the worst drought in living memory.

The families who until a few months ago herded these animals across northern Kenya and beyond now huddle in this riverside settlement, their children prone to malaria and other illnesses, but at least close to a reliable source of water. Now they are completely dependent on aid handouts for most of their food.

'Our whole life has been spent moving, but we are desperate people. People who have lost our livelihood,' says Mukhtar Aden, one of the elders at the Quimbiso settlement. 'We didn't settle here by choice, it was forced upon us.'

Everywhere are tales of huge livestock losses. In one roadside settlement, which now depends on selling milk from its few remaining animals to passing trucks, a man produces a book recording the dark days of the drought. One entry, for 15 February, shows that the community lost more than 500 sheep and goats and 250 cattle in a single day.

And while rain did came to the region for the first time in more than a year last month, it was too late for the makeshift roadside communities who no longer have animals to put out to pasture.

Wargadud is another sizeable community running along either side of the region's main road. The chairman of Wargadud's water users' association is Abdullahi Abdi Hussein, who describes how the periods of rain have got shorter and the dry spells longer - changing the pattern of four seasons on which the pastoral communities depended.

And while there were always droughts, he says: 'Decade after decade it has been getting more severe. It has only been getting harder and harder and more and more serious.'

Though alarming, the figures confirm expectations. "They make intuitive sense to me," says Jim Watson, deputy leader of the energy programme at the Tyndall Centre for Climate Change Research, UK.

One likely contributor is China, whose emissions slowed at end of the 1990s before rising again. China is now the world's second largest emitter of greenhouse gases after the US. On Tuesday, the International Energy Agency released a report predicting that it would become the world's top emitter by 2030 (see World faces 'dirty, insecure' energy future).

Other growing developing countries, such as India and Brazil, are also fast becoming large emitters.

The US, meanwhile, is taking no nationwide action to reduce greenhouse gas emissions. And the European Union Emissions Trading Scheme - created to help EU nations abide by their agreed Kyoto Protocol emissions limits - failed to do so in 2005, its first year of operation. It is unlikely to do so until its second phase of operation, which begins in 2008.
Unacceptably high

The Global Carbon Project report shows that carbon dioxide emissions over the last five years resembled one of the scenarios which the Intergovernmental Panel on Climate Change uses to predict how the world will change with greenhouse gas emissions. The "A1B" scenario assumes that 50% of energy over the next century will come from fossil fuels, resulting in atmospheric carbon dioxide concentrations causing drastic climatic consequences.

"On our current path, we will find it extremely difficult to rein in carbon emissions enough to stabilise the atmospheric CO2 concentration at 450 parts per million and even 550 ppm will be a challenge," says Josep Canadell, executive director of the Global Carbon Project.

Research suggests that stabilising carbon dioxide concentrations at 450 ppm could limit global warming to 2°C.
Environmental inertia

The authors also highlight the importance of environmental inertia. This is the mechanism by which the environment stores up part of the energy of generated by greenhouse gas emissions, only releasing it to the atmosphere later on.

As a result, even when human emissions do begin to drop, atmospheric carbon dioxide will continue to rise for up to a century. Global temperatures will continue to increase for two or more centuries.

"This report shows how important it is for all countries to work towards more ambitious climate targets within the next phase of international action beyond 2012," says Watson.

He adds: "Action to persuade the US and large developing countries such as China and India to work towards such an agreement is particularly crucial. So is the acceleration of technological co-operation initiatives to help developing countries - particularly China - to move to a lower carbon development pathway."

In 2000, an experimental plane loaded with instruments for measuring various particles in the atmosphere flew over Iceland shortly after an eruption of the Hekla volcano there. "It was running some of the instruments when it intercepted the volcanic plume - totally by accident," explains Genevieve Millard, an earth scientist at the University of Cambridge, UK.

Surprisingly, the plane's data showed that ozone levels were practically nonexistent within the ribbon-like plume.

Researchers looking for ozone depletion after volcanic eruptions have traditionally focused on the effect of particles of volcanic sulphate, which comes from the sulpur dioxide gas emitted during an eruption.

Instead, Millard's team found nitric acid and ice particles were the ozone hole culprits. These particles would normally have needed lower temperatures in order to form, but Millard believes that the high concentrations of nitric acid and water vapour in the plume allowed them to condense at warmer-than-usual temperatures.

Their presence is critical, as these chemicals cause volcanic chlorine gases to become energised and reactive in the atmosphere. It is this active chlorine that starts to react with ozone, breaking it down and creating holes, Millard believes.
Patched up

The resulting mini-ozone hole was shallow and effectively patched up within days, the researchers say. This is because the Hekla eruption was small and the plume did not penetrate deep into the ozone layer.

Within two days, the 'thicker' top of the ozone layer had compensated for the small hole. Millard compares this process to poking into a rubber sheet: the sides get dragged in and fill the indentation. By 12 days, even the ozone levels in the lowermost stratosphere had been patched up.

"The most important thing," says Millard, "is that the plume got into the stratosphere."

She and her colleagues are now looking at a much larger eruption - Mount Pinatubo in the Philippines in 1999 - to see if larger eruptions will mean larger holes in the ozone layer.

"For example, is there significant loss of ozone and increased ultra-violet radiation at low latitudes following large explosive eruptions?" questions team member David Pyle, at the University of Oxford, UK. "We want to understand this, so that we can have a better picture both of what might have happened in the past and of what may happen in the future."

Journal reference: Geophysical Research Letters (doi:10.1029/2006GL026959) and Journal of Geophysical Research (doi:10.1029/2005JD006872)

The temblor, as measured on the open-ended Moment Magnitude scale, struck at 10:26 pm (2:02 GMT Monday), with its epicenter located 212 kilometers (130 miles) northeast of Santiago del Estero city, at a depth of 550 kilometers (342 miles), the service said.

The Pacific Tsunami Warning Center at Ewa Beach, Hawaii, said there was no risk of a Pacific-wide tsunami "based on historical earthquake and tsunami data."

However, the center warned that "earthquakes of this size sometimes generate local tsunamis that can be destructive along coasts located within 100 kilometers (60 kilometers) of the earthquake epicenter."

The archipelago nation is part of the Pacific Ocean's "ring of fire," where earthquakes of this magnitude are common and rarely cause serious damage.