Sooner or later, a catastrophe from space will wipe out almost all life on Earth, according to Dr Arnon Dar of the Technion Space Research Institute in Israel. A particular type of exploding star going off anywhere in our region of the Universe would devastate our planet.
Using the latest statistics and calculations, Dar says that a supermassive star collapsing at the end of its lifetime would form a black hole and send out a beam of destructive radiation and particles that would sterilize any planet in its path. The odds are that any planet in our galaxy would be affected about once every one hundred million years. "It is a certainty; the timescales are comparable to mass extinctions seen in Earth's geological record," he says.
Supermassive stars, those with a mass substantially greater than our Sun, are scattered throughout the galaxy. When they collapse at the end of their lives, they eject an intense beam of gamma-rays into space. These rays are so powerful that they could have a major influence on life in our galaxy. "If such a beam were to strike Earth, the effects would be totally devastating, unlike anything we could imagine," Dar says.
On the side of Earth facing the explosion, searing shock waves will begin to rip through the atmosphere, igniting infernos when they reach the ground. Within moments of the arrival of the radiation from deep space, the atmospheric temperature will begin rising rapidly, wrecking global weather systems. All organic material on the surface of Earth will start to burn.
The initial gamma-ray burst will last only a fraction of a second, but almost immediately afterwards will come the cosmic rays, which will drench our planet for days. Cosmic rays are highly energetic particles travelling through space at almost the speed of light. They will slam into the atmosphere, depositing vast amounts of energy and creating swarms of destructive particles, called muons, that penetrate hundreds of feet into rocks so that even deep-sea creatures will be affected by lethal doses of radiation.
The Earth's ecosystem will be destroyed. "The few who might survive will wish they had died," says Dar. "They will struggle, forlornly, on a wrecked planet." He points out that many of the great extinctions that regularly punctuate the Earth's history are consistent with being caused by a devastating influx of radiation from space. "Direct proof that it happened this way is lacking at present," he says, "but many people are looking for it."
Because the gamma-ray bursts from collapsing supermassive stars are shot across the cosmos in narrow beams, probably no more than a degree across, most of them will miss the Earth. However, the latest statistics suggest once every one hundred million years or so, they will hit us. This is about the rate of global extinctions on Earth.
At the moment, astronomers do not know which star to watch. Stars like the supermassive Eta Carinae, which is visible in the Southern Hemisphere, are likely to explode and send out a gamma-ray burst sometime in the next million years or so. But this particular star isn?t pointing in our direction.
Somewhere, a star is pointing our way, but astronomers haven?t found it yet. Dar says, ?Perhaps one day we will be able to tell which stars are threatening."
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We don?t know for sure why the dinosaurs died out, but scientists are about to test their favorite theory. Palaeontologists suspect that about 65 million years ago a giant meteorite hit the Earth. It may have been accompanied by severe volcanic activity.
A thin layer of clay found all around the world contains iridium, which is a rare element but one that meteorites have quite a lot of. Dinosaur bones are found below this clay layer. The impact of a meteorite this size would have made life on Earth unlivable for large creatures, with no sunlight for years and nothing to eat. Some mammals did survive (and they became us). Some dinosaurs survived as well, and live among us now as birds.
Now scientists have drilled a core of earth from a crater in the Gulf of Mexico called the Chicxulub crater. They think this might be the site of the meteorite's impact and are getting ready to analyze the core. The crater wasn?t spotted before because it was buried beneath miles of limestone. It is 20 times deeper than the Grand Canyon.
Want to find out what?s out in space that may be heading our way? Read ?Dark Matter, Missing Planets & New Comets? by Tom Van Flandern, click here.
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