Geological evidence shows that a giant meteorite about six miles wide smashed into the Yucatan Peninsula close to the current Mexican town of Chicxulub 65 million years ago. According to the standard theory, the impact set off volcanic eruptions, massive earthquakes and tsunamis that sent dust flying high into the atmosphere, where it lingered and blocked the Sun's light for decades or centuries.

Deprived of the sun's life-giving rays, plants and animals began to die. The dark skies also caused temperatures to plummet and white-hot debris falling back to Earth ignited wildfires all over the globe, the smoke of which mixed with rain clouds to create a scalding acid downpour. Many scientists believe the combined calamities killed off most of the life on Earth, including dinosaurs, in the so-called K-T extinction event .

A small team of scientists, however, have argued that a single meteorite was not enough to end the dinosaurs' reign, and that the Yucatan impact occurred 300,000 years too early. The biggest proponent of this alternative scenario is Gerta Keller of Princeton University.

Keller thinks that the Chicxulub impact, combined with volcanoes in India and global warming, only upset the ecological balence, causing many species to shrink in size. But these things weren't enough to trigger a mass extinction, she believes. Instead, Keller speculates that a second, currently unidentified meteor crashed sometime after Chicxulub.

But a new examination of sediments taken from the Demerara Rise in the Atlantic Ocean casts fresh doubt on Keller's minority view.

Located some 3,000 miles from the Yucatan Peninsula, the Demerara Rise is considered an intermediate distance from the impact site. Interpretation of samples collected from locations close to the crater are complicated by factors such as waves, earthquakes and landslides that were triggered by the impact and which shuffle the sediment layers. Samples from farther away, meanwhile, receive little impact debris and are much less helpful in recreating events.

The Demerara Rise sample thus provides an unusually clear picture of the events at the time of the mass extinction that claimed the dinosaurs. Analysis revealed a unique layer composed of impact-related material, but none above or below that layer.

The Demerara Rise sediment, therefore, shows "no support for multiple impacts or other stresses leading up to or following the deposition of material from the impact," MacLeod said.

The team's findings are detailed in an online version of the Geological Society of America Bulletin.

No airplanes crashed, and astronomers said the event was probably a "bolide," a random meteor that could have been natural or man-made.

Morgan County Sheriff Chief Deputy Mike Corley said the reports came from southern Morgan County and Cullman County. Firefighters and various police agencies searched the area but found no crash site.

"(We found) no fires, no explosions or anything to explain it," said Corley. "It was like a falling star."

Decatur astronomer Loren Ball said the bolide likely came from "space junk." He said the North American Aerospace Defense Command is tracking 9,000 pieces of man-made junk including nuts, bolts, gloves and pieces of expired satellites that, because of friction with the upper atmosphere, are gradually approaching Earth.

The lime-green color, Ball said, is consistent with the color that would come from burning aluminum as it entered Earth's atmosphere.

The fact that the object broke into pieces is no surprise, whether the object was natural or man-made. Moving at 10 to 40 miles per second, it would generate tremendous energy, much of it in the form of light. He said a bolide the size of a golf ball generates enough light to trigger calls to the media.

"Something like this happens every day, but there are not always people around to see it," Ball said.

Space junk

According to some studies, there are 4 million pounds of space junk - as many as 110,000 objects larger than 1 centimeter - in low-Earth orbit. They provide a brilliant display on Earth, but can be hazardous to astronauts.

A small speck of paint from a satellite shooting around the Earth once dug a quarter-inch pit in a space shuttle window.

Earth's atmosphere extends 250 miles above its surface, Ball said, a fact that forces the International Space Station and the Hubble Space Telescope to periodically correct their orbit so they won't be pulled into a downward spiral.

Gene Byrd, professor of astronomy at The University of Alabama, said the sightings were too late to be explained by a meteor shower that took place last week.

Bolide explanation

He said the composition of the bolide could explain its greenish color, but the human eye might also explain it. The eye has greater sensitivity to blue and green colors, he said.

Byrd's guess was that it was "a large, sporadic meteor." He said such meteors occasionally emit a sonic boom, and usually are rock fragments from the asteroid belt.

In the 1950s, he said, a small meteor actually struck a woman in Sylacauga, sending her to the hospital with a severe bruise. Astronomers believe a 10-mile-wide meteor that hit Mexico caused the extinction of the dinosaurs, Byrd said.

Corley said he saw the event from his home.

"It did have an unusual color. It had a bright, glowing, lime-green color to it," Corley said.

The Alabama sightings came a day after a similar green fireball was seen in the skies above Australia.

Meteorologists there identified the object as a meteor, likely produced as the Earth passed through the tail of the comet Tempel-Tuttle according to news reports.

Last week, a Russian cosmonaut hit a golf ball into orbit from the International Space Station as part of a publicity campaign to raise money for the Russian space program.

The golf ball joined the other pieces of space junk that will eventually burn up in the upper atmosphere.

Measuring 6.2 on the Richter scale the quake rocked Ternate and nearby islands on eastern Indonesian province of North Maluku at 0132 GMT, said an official at Jakarta's Meteorology and Geophysics Agency. The quake's epicentre was in the sea, about 228 kilometres northeast of Ternate, the provincial capital of North Maluku, and occured about 72-kilometres beneath the sea bed, according to the official, who identified herself as Eva.

There were no immediate reports of injury or structural damage from the latest earthquakes to jolt Indonesia in recent weeks.

Indonesia, the world's largest archipelago nation, is prone to earthquakes because of its location on an arc of volcanos and oceanic trenches encircling the Pacific Basin.

The basic thunderstorm occurs when you have strong updrafts in a building storm. As the water droplets bustle around inside the clouds, they can build up an electric charge -- much like how if you wear socks on a carpet, you build up a charge if you scuffle them around. When the charge gets big enough, and it finds a release, that electric current is what you see as lightning.

To get those strong updrafts, you generally need much colder air moving in at the upper levels of the atmosphere. Since warm air rises, having much colder air aloft allows the air to rise farther, making for a bigger storm.

It is more difficult to get thunderstorms when temperatures are very low, but there's no real maximum temperature required to form a thunderstorm; what you need is a large relative difference in temperature between the ground and the upper levels.

In other words, as a rough example, having it be 28 on the ground and, say, 0 degrees above would work in a similar way as a 68 degree reading on the ground and a 40 degree reading above (again a rough example. It's not really that linear in true life due to other factors, but the idea is the same.)

Thunderstorms are already somewhat rare here because of our temperate climate. We normally don't get the big temperature differences to trigger thunderstorms. But with the arctic air moving in, we were able to get a decent difference in temperature.

But that was just one part of it. A second factor, the Puget Sound Convergence Zone also greatly helped in the creating favorable ingredients.

We had those arctic winds from the north colliding with the typical warmer winds from the south. Where those winds collided on the ground, they were forced up into the air -- helping trigger a strong updraft. The colder air moving in allowed those updrafts to get even higher and create the heavy snow and lightning.

"Almost all of the systems that have been looked at are in positive feedback ... and soon those effects will be larger than any of the effects of carbon dioxide emissions from industry and so on around the world," he added.

Scientists say that global warming due to carbon emissions from burning fossil fuels for power and transport could boost average temperatures by up to 6C by the end of the century causing floods, famines and violent storms.

But they also say that tough action now to cut carbon emissions could stop atmospheric concentrations of CO2 hitting 450 parts per million -- equivalent to a temperature rise of 2C from pre-industrial levels -- and save the planet.

Lovelock said temperature rises of up to 8C were already built in and while efforts to curb it were morally commendable, they were wasted.

"It is a bit like if your kidneys fail you can go on dialysis -- and who would refuse dialysis if death is the alternative. We should think of it in that context," he said.

"But remember that all they are doing is buying us time, no more. The problems go on," he added.

REFUGE

Lovelock adopted the name Gaia, the Greek mother earth goddess, in the 1960s to apply to his then revolutionary theory that the earth functions as a single, self-sustaining organism. His theory is now widely accepted.

In London to give a lecture on the environment to the Institution of Chemical Engineers, he said the planet had survived dramatic climate change at least seven times.

"In the change from the last Ice Age to now we lost land equivalent to the continent of Africa beneath the sea," he said. "We are facing things just as bad or worse than that during this century."

"There are refuges, plenty of them. 55 million years ago ... life moved up to the Arctic, stayed there during the course of it and then moved back again as things improved. I fear that this is what we may have to do," he added.

Lovelock said the United States, which has rejected the Kyoto Protocol on cutting carbon emissions, wrongly believed there was a technological solution, while booming economies China and India were out of control.

China is building a coal-fired power station a week to feed rampant demand, and India's economy is likewise surging.

If either suddenly decided to stop their carbon-fuelled development to lift their billions of people out of poverty they would face a revolution, yet if they continued, rising CO2 and temperatures would kill off plants and produce famine, he said.

"If climate change goes on course ... I can't see China being able to produce enough food by the middle of the century to support its people. They will have to move somewhere and Siberia is empty and it will be warmer then," he said.