Skip to comments.Did a gamma-ray burst devastate life on Earth?
Posted on 09/24/2003 2:05:01 PM PDT by LibWhacker
A DEVASTATING burst of gamma-rays may have caused one of Earth's worst mass extinctions, 443 million years ago. A team of astrophysicists and palaeontologists says the pattern of trilobite extinctions at that time resembles the expected effects of a nearby gamma-ray burst (GRB). Although other experts have greeted the idea with some scepticism, most agree that it deserves further investigation.
GRBs are the most powerful explosions known. As giant stars collapse into black holes at the end of their lives, they fire incredibly intense pulses of gamma rays from their poles that can be detected even from across the universe for 10 seconds or so. All the bursts astronomers have recorded so far have come from distant galaxies and been harmless on the ground, but if one occurred within our galaxy and was aimed straight at us, the effects could be devastating, according to astrophysicist Adrian Melott of the University of Kansas in Lawrence.
The Earth's atmosphere would soak up most of the gamma rays, Melott says, but their energy would rip apart nitrogen and oxygen molecules, creating a witch's brew of nitrogen oxides, especially the toxic brown gas nitrogen dioxide that colours photochemical smog (see Graphic).
Melott estimates that a burst would produce enough of the gas to darken the sky, blotting out half the visible sunlight reaching the Earth. Nitrogen dioxide would also destroy the ozone layer, exposing surface life to a dangerous overdose of ultraviolet radiation from the sun for a year or more until the ozone recovered.
The idea that GRBs could have affected the course of evolution was first suggested two years ago (New Scientist, 15 December 2001, p 10). John Scalo and Craig Wheeler of the University of Texas at Austin estimated that GRBs close enough to affect life in some way might occur once every 5 million years or so- around a thousand times since life began. Now Melott believes he has palaeontological evidence that this actually happened at the end of the Ordovician period 443 million years ago, causing one of the five largest extinctions of the past 500 million years. Working with Bruce Lieberman, a specialist in fossil trilobites also at the University of Kansas, and other colleagues, he looked at the pattern of extinctions in the late Ordovician.
The researchers found that species of trilobite that spent some of their lives in the plankton layer near the ocean surface were much harder hit than deep-water dwellers, which tended to stay put within quite restricted areas. Usually it is the more widely spread species that fare better in extinctions. Melott says this unusual pattern could be explained by a GRB, which would probably devastate creatures living on land and near the ocean surface, but leave deep-sea creatures relatively unharmed (http://www.arxiv.org/abs/astro-ph/0309415).
Previous theories blame the two extinctions that occurred in the late Ordovician period on the start and end of an ice age at the time. But it is hard to explain what triggered the ice age itself, which started very suddenly at a time when the climate was quite warm.
Continental changes would have taken too long, and climate models have not been able to replicate the ice age. But a GRB that blocked out the sun could have caused it, points out Pat Brenchley, a retired palaeoecologist from the University of Liverpool, UK, calling the idea" an interesting alternative". "I'd like to see a lot more information," says Peter Sheehan of the Milwaukee Public Museum, who has studied the Ordovician extinctions.
When Sheehan looked at the pattern of extinctions among brachiopod species, he found that 90 per cent of the widespread species survived, compared with only 10 per cent of those living in restricted areas. This is the normal pattern during extinctions. He thinks that glaciation alone might have killed off shallow-water species by draining water from shallow continental seas. Mellot concedes that a lot more work needs to be done, but is optimistic: "We think it's a good hypothesis."
Written by Jeff Hecht
New Scientist issue: 27 September 2003.
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No, it was because George W. Bush didn't sign Kyoto.
Signs of the End of the Age
1Jesus left the temple and was walking away when his disciples came up to him to call his attention to its buildings. 2"Do you see all these things?" he asked. "I tell you the truth, not one stone here will be left on another; every one will be thrown down." 3As Jesus was sitting on the Mount of Olives, the disciples came to him privately. "Tell us," they said, "when will this happen, and what will be the sign of your coming and of the end of the age?" 4Jesus answered: "Watch out that no one deceives you. 5For many will come in my name, claiming, 'I am the Christ, ' and will deceive many. 6You will hear of wars and rumors of wars, but see to it that you are not alarmed. Such things must happen, but the end is still to come. 7Nation will rise against nation, and kingdom against kingdom. There will be famines and earthquakes in various places. 8All these are the beginning of birth pains. 9"Then you will be handed over to be persecuted and put to death, and you will be hated by all nations because of me. 10At that time many will turn away from the faith and will betray and hate each other, 11and many false prophets will appear and deceive many people. 12Because of the increase of wickedness, the love of most will grow cold, 13but he who stands firm to the end will be saved. 14And this gospel of the kingdom will be preached in the whole world as a testimony to all nations, and then the end will come. 15"So when you see standing in the holy place 'the abomination that causes desolation,' spoken of through the prophet Daniel--let the reader understand-- 16then let those who are in Judea flee to the mountains. 17Let no one on the roof of his house go down to take anything out of the house. 18Let no one in the field go back to get his cloak. 19How dreadful it will be in those days for pregnant women and nursing mothers! 20Pray that your flight will not take place in winter or on the Sabbath. 21For then there will be great distress, unequaled from the beginning of the world until now--and never to be equaled again. 22If those days had not been cut short, no one would survive, but for the sake of the elect those days will be shortened. 23At that time if anyone says to you, 'Look, here is the Christ!' or, 'There he is!' do not believe it. 24For false Christs and false prophets will appear and perform great signs and miracles to deceive even the elect--if that were possible. 25See, I have told you ahead of time. 26"So if anyone tells you, 'There he is, out in the desert,' do not go out; or, 'Here he is, in the inner rooms,' do not believe it. 27For as lightning that comes from the east is visible even in the west, so will be the coming of the Son of Man. 28Wherever there is a carcass, there the vultures will gather. 29"Immediately after the distress of those days
" 'the sun will be darkened, and the moon will not give its light; the stars will fall from the sky, and the heavenly bodies will be shaken.'
 30"At that time the sign of the Son of Man will appear in the sky, and all the nations of the earth will mourn. They will see the Son of Man coming on the clouds of the sky, with power and great glory. 31And he will send his angels with a loud trumpet call, and they will gather his elect from the four winds, from one end of the heavens to the other. 32"Now learn this lesson from the fig tree: As soon as its twigs get tender and its leaves come out, you know that summer is near. 33Even so, when you see all these things, you know that it is near, right at the door. 34I tell you the truth, this generation will certainly not pass away until all these things have happened. 35Heaven and earth will pass away, but my words will never pass away.