Ray burst is extinction suspect

**Parihaka** · 04-11-2005, 17:05 PM

http://news.bbc.co.uk/1/hi/sci/tech/4433963.stm

Quote:

Gamma ray bursts are the most powerful explosions known
A huge cosmic explosion could have caused a mass extinction on Earth 450 million years ago, according to an analysis by scientists in the US.
A gamma ray burst could have caused the Ordovician extinction, killing 60% of marine invertebrates at a time when life was largely confined to the sea.

These cosmic blasts are the most powerful explosions in the Universe.

The scientists think a 10-second burst near Earth could deplete up to half of the planet's ozone layer.

We don't know exactly when one came, but we're rather sure it did come - and left its mark

Dr Adrian Melott, University of Kansas

With the ozone layer devastated, the Sun's ultraviolet radiation could have killed off much of the life on land and near the surface of oceans and lakes.

Gamma ray bursts are rare occurrences, but scientists estimate that at least one must have occurred near the Earth in the past one billion years.

Scientists think that gamma-ray bursts are generated in two principal scenarios. In one scenario, a star collapses in on itself, giving birth to a black hole and releasing a high-energy jet of material travelling at close to the speed of light.

The bursts could also be generated when two neutron stars collide.

"A gamma ray burst originating within 6,000 light-years from Earth would have a devastating effect on life," said co-author Dr Adrian Melott, an astronomer at the University of Kansas, US.

"We don't know exactly when one came, but we're rather sure it did come - and left its mark. What's most surprising is that just a 10-second burst can cause years of devastating ozone damage."

Surface-dwellers

Dr Melott and his colleagues used computer models to calculate the effects of a nearby gamma ray burst on the Earth's atmosphere and its life forms.

They showed that up to half the ozone layer would be destroyed within weeks. Five years on, at least 10% would still be missing.

During the Ordovician, most life forms still lived in the sea

Although deep sea creatures would be protected from the effects of the burst, surface-dwelling plankton and other life near the top of the ocean would not survive.

This would have had huge implications for other life forms, because plankton form the foundation of the marine food chain; they provide for animals which are then eaten by larger species.

Bruce Lieberman, a palaeontologist at the University of Kansas, originated the idea that a gamma ray burst could have caused the Ordovician extinction. An ice age has been implicated by other scientists in the extinction.

The latest research shows that a gamma ray burst could have caused a fast die out early on and could also have triggered a drop in temperature similar to the effect of an ice age.

Swift, a Nasa space mission launched in November 2004, is currently investigating the phenomenon of gamma ray bursts from Earth orbit.

Ray · 04-11-2005, 17:53 PM

Ray burst?

That caught my eye.

I was worried that someone thought I was a balloon and about to burst.

My waist is 32 inches!

**Parihaka** · 04-11-2005, 18:05 PM

So now the truth is out, you're responsible for the mass extinction of dinosaurs!

Ray · 04-12-2005, 02:19 AM

dalem · 04-12-2005, 12:48 PM

Ozone depletion is overrated as a large-scale forcing event.

-dale

Broken · 04-16-2005, 23:50 PM

Quote:

Originally Posted by dalem

Ozone depletion is overrated as a large-scale forcing event.

-dale

Ozone is a major UV blocker in the atmosphere. Us bigger organisms, especially the furry ones, can deal with low ozone, but marine photo-synthesizers and plankton tend to get very unhappy and die. So a mass die-off of marine organisms would be understandable if their food-supply (the plankton) were gone.

Speaking of Gamma-ray Bursters, the shock wave from a small one hit the earth back in December. The burster was located about 20,000 light-years away near the galactic core. Fortunately for us. Even so, every gamma-ray detector in orbit was knocked offline and the wavefront made a dent 30-miles deep in the Earth's ionosphere.

The burster was a midget, it only converted a mass equivalent to half the sun into pure energy in a fifth of a second. A real pip-squeak.

The Chap · 04-27-2005, 01:07 AM

The initial burst is one thing. The eventual effect is even more interesting. Compacting and ionising the interstallar medium along a shock-wave front .

04-27-2005, 01:07 AM	#7 (permalink)
The Chap *Senior Contributor* Join Date: 08-18-04 Location: UK Posts: 1,181 Country:	The initial burst is one thing. The eventual effect is even more interesting. Compacting and ionising the interstallar medium along a shock-wave front . __________________ Where's the bloody gin? An army marches on its liver, not its ruddy stomach.

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04-11-2005, 17:53 PM	#2 (permalink)
Ray Postmaster General *Military Professional* Join Date: 08-20-03 Posts: 26,144 Country:	Ray burst? That caught my eye. I was worried that someone thought I was a balloon and about to burst. My waist is 32 inches!

04-11-2005, 18:05 PM	#3 (permalink)
Parihaka Moderator Join Date: 11-10-04 Location: Te Ika a Maui Posts: 9,465 Country:	So now the truth is out, you're responsible for the mass extinction of dinosaurs!

04-12-2005, 02:19 AM	#4 (permalink)
Ray Postmaster General *Military Professional* Join Date: 08-20-03 Posts: 26,144 Country:

04-12-2005, 12:48 PM	#5 (permalink)
dalem Lord High Hullabalooster *Senior Contributor* Join Date: 11-23-04 Location: Columbia Heights, MN Posts: 8,323 Country:	Ozone depletion is overrated as a large-scale forcing event. -dale

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