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Mass Extinctions (Overall; In General)

rynner2

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The earliest Meteor extinction event? Link.
Ellwood and four other researchers have just published an article in the journal Science in which they tie an early mass extinction to a meteor strike. This extinction happened 380 million years ago in what is called the middle Devonian. It was a time when only small plants, wingless insects and spiders inhabited the land and everything else lived in the sea. About 40 percent of all species disappeared from the fossil record at this time.

The extinction has been known to geologists for a long time but this is the first time it has been tied to a meteor strike. This is also the oldest known impact that has been tied to a mass extinction.

Ellwood is quick to point out that because the extinction and the meteor strike happened at the same time does not prove the impact caused the extinction -- but it certainly suggests it.
...
The past 550 million years are divided up by geologists into about 90 "stages." Each stage is distinguished from another by a change in the fossil record. To date, only four of these stages show strong evidence of a meteor strike, Ellwood's discovery being the latest, as well as the oldest. The most recent, best known extinction is the K-T boundary at which the dinosaurs died out, about 65 million years ago. There have been five major mass extinctions and many smaller ones since then.

"We know that meteors have struck the Earth hundreds of times," Ellwood said. "If I had to guess, I would say that once every 5 million years a meteor big enough to cause a mass extinction hits the Earth.

"We could protect ourselves if we wanted. We went to the moon, we can figure out how to destroy or deflect a meteor. All it takes is the political will -- and an awareness of the threat."
 
Actually, last week's New Scientist had an article explaining the proposition that at least some of the mass extinction impacts were caused by flood basalts rather than asteroids. (Basically, a mantle plume causes a section of crust to collapse, and ejects a lump of material that then causes the crater.) But can I find a reference on their website now? No. But they do have this story.

That's one of NS's problems, they sometimes forget earlier research they published contrary to the current story. So you read one week that Theory A is the latest and greatest idea, then the next week Theory B is where everyone is looking, and no-one mentions Theory A at all.
 
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Hmmmmmmmmm its interesting that the answer might be:

d) None of the above

e) All of the above

Volcanoes, asteroids and mass extinctions


Neither massive volcanic eruptions nor extraterrestrial impacts are sufficiently powerful on their own to cause mass extinctions of life on Earth, research by University of Leicester geologists suggests.

Instead, both events coincidentally occurring together may be required to cause the worst mass extinctions.

In the last 300 million years, life on Earth has suffered three major mass extinctions: those of the end-Permian, end-Triassic and end-Cretaceous periods.

The third of these, leading to the demise of the dinosaurs 65 million years ago, is believed to be caused by a meteorite colliding with the Earth, combined with the eruption of huge floods of basaltic lava.

Controversy rages over whether all three mass extinctions involve a similar combination of impact and volcanism, and if they did, whether this is due to random chance or whether there is any causal link between impact and volcanism.

Dr Rosalind White, Royal Society Dorothy Hodgkin Research Fellow, and Professor Andrew Saunders, both of the University of Leicester Department of Geology, recently looked at the statistical probability of any link between impact and eruptions to see whether it is credible that they occur during the same period by coincidence alone.

Their re-evaluation of the frequency of bolide (extraterrestrial) impacts and massive ‘flood basalt’ volcanism indicates that both events occur individually much more frequently than the incidence of mass extinctions.

This suggests that each, on its own, is not powerful enough to trigger a disastrous worldwide collapse of ecosystems that would lead to a mass extinction.

The occurrence of flood basalts (caused by the outpourings of basaltic lava) and bolide impact may both be necessary to lead to the largest mass extinctions the planet has known.

That begged the question as to what the likelihood was of the two events occurring over the same period, if they were not linked.

Here, Professor Saunders’ and Dr White’s statistical analysis showed that three random coincidences involving both impact and volcanism over the last 300 million years are likely, and there would not necessarily have to be any link between them.

They therefore suggest that theories implying that flood basalts are generated by bolide impacts are unnecessary and unproven.

Rosalind White explained the scale of events that cause flood basalts: “Massive continental flood basalt provinces occur when immense outpourings of basaltic lava are formed by localised partial melting in anomalously hot regions of the Earth’s mantle (the solid layer of rock between the Earth’s core and crust).

“A typical continental flood basalt would cover an area five times that of the UK, with lava exceeding 1 km in thickness, made up of hundreds of individual lava flows, each coming from an enormous volcanic eruption that may have lasted decades.

“Eruptions are separated by periods of inactivity that can last hundreds or thousands of years. The total time taken to erupt an entire continental flood basalt province is probably approximately 1-5 million years, though in most cases, the dating is not precise enough for us to know this duration accurately.”

A report on the research carried out by Dr Rosalind White and Professor Andrew Saunders is to be published later in the year by the geological journal Lithos.




More information:
http://www.le.ac.uk

http://www.innovations-report.com/html/reports/earth_sciences/report-29308.html
 
anome said:
Actually, last week's New Scientist had an article explaining the proposition that at least some of the mass extinction impacts were caused by flood basalts rather than asteroids. (Basically, a mantle plume causes a section of crust to collapse, and ejects a lump of material that then causes the crater.) But can I find a reference on their website now? No. But they do have this story.

That's one of NS's problems, they sometimes forget earlier research they published contrary to the current story. So you read one week that Theory A is the latest and greatest idea, then the next week Theory B is where everyone is looking, and no-one mentions Theory A at all.
That was the 'Verneshot' theory.
 
That's the particular theory in this instance, but they do it all the time.

The Verneshot proponents had decided, in contrast to the analysis given above, that the impacts were too unlikely to coincide with the flood basalts, and as the flood basalts predated the impacts, the impacts can't have caused the flood basalts, so maybe the flood basalts caused the impacts.

Don't know if it makes any sense, myself. Not really up on geology.
 
I don't really buy the idea that flood basalts can lead to a large crater as I'm not actually aware of an associated one - they tend to lead to higher areas (the Ethiopian Plateau, the Deccan Traps, Iceland, etc.). Also 'impact' craters tend not to be associated with flood basalts.

That said I'd need to read the article ;)

Emps
 
Ok. So what is the actual 'trigger' for a flood basalt event?:eek:
 
A mantle plume.

Roughly, off the top of my head, The mantle plume causes the flood basalt, and a pocket of gas under a section of crust forms. This pocket collapses, but that's not what causes the impact crater. The collapse of the pocket causes a lump of crust to be ejected into the air, usually coming down near the site of the plume, but possibly moving much further, depending on the size of the plume.

They claim that Tunguska may have been such an event. Need to look at their evidence again.
 
Interesting but I'm still not buying it - flood basalts are much slower processes that that and the plume rarely gets close to the surface - the magma seeps up through the crust through any available cracks over a wide area (hence the flood part). There was a recent(ish) eruption in Iceland which showed how it works (the name will come to me in a bit).

It sounds like the authors are reaching there ;)

Emps
 
Yeah, I'm unconvinced. It could happen that way, but...

I think the timescale issue is addressed by it being caused by the outgassing, not the actual plume itself.
 
It is interesting to note that the giant impacts on Mars which caused the Hellas and Argyre basins, at the very end of the Noachian period, both are diametrically opposite to the highest volcanoes in the solar system; Olympus Mons, Pavonis Mons and so on...

one theory says that the impacts caused these volcanoes, as they will have been in the focus of the shockwaves that travelled through the red planet.

if impacts caused these giant volcanic events on Mars, then perhaps a similar effect sometimes occurs on Earth.
 
Verneshots

Wed 19 May 2004

9:50am (UK)
Science Watch

By John von Radowitz, Science Correspondent

DID A ‘VERNESHOT’ SEE OFF THE DINOSAURS?

The dinosaurs might not have been the victims of a giant asteroid after all.

They could have been blown out of existence by an almighty underground explosion with the energy of seven million atom bombs, according to a new theory.

A team of scientists claims the Earth-shaking blast, called a Verneshot, is the best explanation for why the dinosaurs were wiped out 65 million years ago.

Most experts believe the extinction was caused by a huge asteroid or comet that smashed into the Earth off the coast of Mexico.

Others have blamed a mega-volcanic episode, called a continental blood basalt, which resulted in numerous vents pouring poison gas into the atmosphere from a region called the Deccan Traps in India.

But there’s a mystery that neither theory has been able to solve.

The death of the dinosaurs was not the only mass extinction to have occurred since complex life emerged on the Earth 400 million years ago.

In fact there have been four. And each one seems to have coincided both with a continental flood basalt and a meteorite impact, even though the chances of this happening are remote.

The probability of all four extinctions occurring at the same time as an impact and continental flood basalt is one in 3,500.

But according to the new theory from a team of German scientists, a Verneshot could answer the riddle and account for impact evidence such as craters.

The name Verneshot comes from Jules Verne’s book “From the Earth to the Moon” in which a huge cannon shoots astronauts into space.

The theory suggests what might happen if a mantle plume, a stream of lava welling up from deep within the Earth, builds up between a thick chunk of immovable continent called a craton.

If the craton started splitting, or “rifting”, which could occur every 100 million years, the release of pressure would produce a catastrophic gas explosion.

Gases would surge up and burst out at the surface, poisoning the atmosphere and causing severe environmental stress around the world.

The blast would trigger a magnitude 11 earthquake, bigger than any quake ever recorded.

But this would be just a prelude to the main event.

Immediately after the explosion, pressure would plummet in the pipe that carried the gases, causing it to cave in from the bottom upwards.

The collapse would travel up at hypersonic speed, erupting with unimaginable force at the surface and hurling as much as 20 gigatonnes of rock into the stratosphere.

The energy released would be equivalent to 120 billion tonnes of TNT, or seven million of the atom bombs that destroyed Hiroshima at the end of the Second World War.

Debris would rain down from the sky, and dust would blot out the sun to cause the same kind of climate changing effects as an impact from space.

A large piece of rock from a Verneshot blast landing on the Earth would produce a crater in the same way as an asteroid or comet.

An object ejected from the Deccan Traps could explain why the Chicxulub crater, linked to the extinction of the dinosaurs, is so lopsided.

Modellers have concluded that the impactor must have come in from the south-east at an angle of about 20 degrees. That doesn’t rule out a meteorite, but it also fits in with debris flying from the direction of India.

The scientists, led by Jason Phipps Morgan, at the Geomar earth science institute at Kiel University, believe all the impact signatures associated with mass extinctions can be explained by the Verneshot theory,

Deep mantle volcanism, for instance, would bring the rare element iridium to the surface, while the explosion would produce quartz crystals riddled with tiny fractures.

Small blobs of melted rock and carbon particles called fullerines – other hallmarks of a meteorite impact – could also be formed.

Phipps Morgan, whose claims were reported in New Scientist magazine, acknowledges that the theory is very difficult to prove.

The best evidence would be to locate the remains of a Verneshot pipe buried under kilometres of rock. These should show up on seismic images and gravity surveys.

A “circular gravity anomaly” relating to disturbed areas of basaltic rock would be one expected find, says Phipps Morgan.

Though no-one has yet carried out such a survey in detail, large near-circular gravity anomalies have been recorded under the Deccan Traps.

The best clue to a Verneshot event would be to find remains of a projectile inside a crater.

Usually the high-speed approach of a meteorite ensures that it vaporises when it hits the Earth. Verneshot debris, on the other hand, would not travel so fast and should leave some remnants at the crash site.

If rock fragments at the Chicxulub crater were found to originate from the Deccan area of India, it would be strong evidence that the dinosaurs vanished because of a Verneshot.

http://news.scotsman.com/latest.cfm?id=2946232

Oh and I enjoy "blood basalts" - now that would be Fortean in the extreme!! :)

I'm still not buying it:

1. Flood basalts eruptions are far more common than these major impacts.

2. There was no rifting at Deccan - rifting may have occurred much earlier (when the Indian plate split from Africa - you can track the hot spot all across the Indian Ocean until things stabliised when it hit India leading to the accumulation of the Deccan Traps).

3. Where they for the focal point for rifting (in a triple point ridge area) there is no impacts that I know of - examples include the Ethiopian one and all the eruptions around the Tertiary which resulted in the opening of the Atlantic - major examples of which include the Iceland plume (the failed rift arm is the North Sea) and Nigeria (where the failed arm produces another major hydrocarbon reservoir).

4. It is nearly untestable - the major craters are buried and any rock invovled in the imapct would be substantially altered.

Its an interestng theory but they'd need to find a match with the major rifting and/or flood basalt events (eruptions can continue for 10-20 million years some times though) and a means to test it - i.e. a workable model ;)

Emps
 
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I'm not convinced either. As I said, the basic idea behind it is that they expect fewer coincidental flood basalts and meteor impacts. Meanwhile the other people mentioned above think that the number is about right.

Me - I don't know. I'm not a geologist. Either one could be right, but the Verneshot theory does seem to be a tad complicated. As if they thought: "Well, that explains this bit, but how can we manipulate it to explain this without resorting to the original theory?"

As for testability: the traditional hypothesis of a combination of flood basalt and meteor impact isn't testable either, without an event happening. At least we'll die knowing which one was right, I suppose.
 
anome said:
Either one could be right, but the Verneshot theory does seem to be a tad complicated. As if they thought: "Well, that explains this bit, but how can we manipulate it to explain this without resorting to the original theory?"

My feelings exactly - that said I do love the name for the process!!

Emps
 
Jules has a lot to answer for, if you ask me.
 
I always thought Mr Verne should have gone on and written a 20, 000 leagues.. ~ Journey to ... crossover. There's a backstory there somewhere1

:)
 
See the previous threads on specific mass extinctions:

KTE (which killed the dinosaurs):
forteantimes.com/forum/viewtopic.php?t=6466
https://forums.forteana.org/index.php?threads/so-what-really-did-kill-the-dinosaurs.6466/


The Great Dying (which happened in the Permian and was the largest of them all):
forteantimes.com/forum/viewtopic.php?t=15336
https://forums.forteana.org/index.php?threads/the-great-dying-the-permian-triassic-extinction.15336/


and a discussion of their frequency:

Mass extinction comes every 62 million years, UC physicists discover

David Perlman, Chronicle Science Editor

Thursday, March 10, 2005



With surprising and mysterious regularity, life on Earth has flourished and vanished in cycles of mass extinction every 62 million years, say two UC Berkeley scientists who discovered the pattern after a painstaking computer study of fossil records going back for more than 500 million years.

Their findings are certain to generate a renewed burst of speculation among scientists who study the history and evolution of life. Each period of abundant life and each mass extinction has itself covered at least a few million years -- and the trend of biodiversity has been rising steadily ever since the last mass extinction, when dinosaurs and millions of other life forms went extinct about 65 million years ago.

The Berkeley researchers are physicists, not biologists or geologists or paleontologists, but they have analyzed the most exhaustive compendium of fossil records that exists -- data that cover the first and last known appearances of no fewer than 36,380 separate marine genera, including millions of species that once thrived in the world's seas, later virtually disappeared, and in many cases returned.

Richard Muller and his graduate student, Robert Rohde, are publishing a report on their exhaustive study in the journal Nature today, and in interviews this week, the two men said they have been working on the surprising evidence for about four years.

"We've tried everything we can think of to find an explanation for these weird cycles of biodiversity and extinction," Muller said, "and so far, we've failed."

But the cycles are so clear that the evidence "simply jumps out of the data," said James Kirchner, a professor of earth and planetary sciences on the Berkeley campus who was not involved in the research but who has written a commentary on the report that is also appearing in Nature today.

"Their discovery is exciting, it's unexpected and it's unexplained," Kirchner said. And it is certain, he added, to send other scientists in many disciplines seeking explanations for the strange cycles. "Everyone and his brother will be proposing an explanation -- and eventually, at least one or two will turn out to be right while all the others will be wrong."

Muller and Rohde conceded that they have puzzled through every conceivable phenomenon in nature in search of an explanation: "We've had to think about solar system dynamics, about the causes of comet showers, about how the galaxy works, and how volcanoes work, but nothing explains what we've discovered," Muller said.

The evidence of strange extinction cycles that first drew Rohde's attention emerged from an elaborate computer database he developed from the largest compendium of fossil data ever created. It was a 560-page list of marine organisms developed 14 years ago by the late J. John Sepkoski Jr., a famed paleobiologist at the University of Chicago who died at the age of 50 nearly five years ago.

Sepkoski himself had suggested that marine life appeared to have its ups and downs in cycles every 26 million years, but to Rohde and Muller, the longer cycle is strikingly more evident, although they have also seen the suggestion of even longer cycles that seem to recur every 140 million years.

Sepkoski's fossil record of marine life extends back for 540 million years to the time of the great "Cambrian Explosion," when almost all the ancestral forms of multicellular life emerged, and Muller and Rohde built on it for their computer version.

Muller has long been known as an unconventional and imaginative physicist on the Berkeley campus and at the Lawrence Berkeley Laboratory. It was he, for example, who suggested more than 20 years ago that an undiscovered faraway dwarf star -- which he named "Nemesis" -- was orbiting the sun and might have steered a huge asteroid into the collision with Earth that drove the dinosaurs to extinction.

"I've given up on Nemesis," Muller said this week, "but then I thought there might be two stars somewhere out there, but I've given them both up now."

He and Rohde have considered many other possible causes for the 62- million-year cycles, they said.

Perhaps, they suggested, there's an unknown "Planet X" somewhere far out beyond the solar system that's disturbing the comets in the distant region called the Oort Cloud -- where they exist by the millions -- to the point that they shower the Earth and cause extinctions in regular cycles. Daniel Whitmire and John Matese of the University of Louisiana at Lafayette proposed that idea as a cause of major comet showers in 1985, but no one except UFO believers has ever discovered a sign of it.

Or perhaps there's some kind of "natural timetable" deep inside the Earth that triggers cycles of massive volcanism, Rohde has thought. There's even a bit of evidence: A huge slab of volcanic basalt known as the Deccan Traps in India has been dated to 65 million years ago -- just when the dinosaurs died, he noted. And the similar basaltic Siberian Traps were formed by volcanism about 250 million years ago, at the end of the Permian period, when the greatest of all mass extinctions drove more than 70 percent of all the world's marine life to death, Rohde said.

The two scientists proposed more far-out ideas in their report in Nature, but only to indicate the possibilities they considered.

Muller's favorite explanation, he said informally, is that the solar system passes through an exceptionally massive arm of our own spiral Milky Way galaxy every 62 million years, and that that increase in galactic gravity might set off a hugely destructive comet shower that would drive cycles of mass extinction on Earth.

Rohde, however, prefers periodic surges of volcanism on Earth as the least implausible explanation for the cycles, he said -- although it's only a tentative one, he conceded.

Said Muller: "We're getting frustrated and we need help. All I can say is that we're confident the cycles exist, and I cannot come up with any possible explanation that won't turn out to be fascinating. There's something going on in the fossil record, and we just don't know what it is."

Source

They have a graph here.
 
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Interesting.There always seems to be dissussions regarding the various cycles of natural events/catastrophies.It does seem that there are a large number of these (volcanic erruptions, meteor showers etc) events that are 'due' another cycle.The results of some of these would clearly test the very survival of most species of life.Lets hope they dont all come at once and we have the ability to prevent/survive them!!!!
 
Bad news - we are way past our 'extinct by' date

Robin McKie, science editor
Sunday March 13, 2005
The Observer

Some say the world will end in fire, some say in ice, wrote Robert Frost. But whatever is to be our fate, it is now overdue.

After analysing the eradication of millions of ancient species, scientists have found that a mass extinction is due any moment now.

Their research has shown that every 62 million years - plus or minus 3m years - creatures are wiped from the planet's surface in massive numbers.

And given that the last great extinction occurred 65m years ago, when dinosaurs and thousands of other creatures abruptly disappeared, the study suggests humanity faces a fairly pressing danger. Even worse, scientists have no idea about its source.

'There is no doubting the existence of this cycle of mass extinctions every 62m years. It is very, very clear from analysis of fossil records,' said Professor James Kirchner, of the University of California, Berkeley. 'Unfortunately, we are all completely baffled about the cause.'

The report, published in the current issue of Nature, was carried out by Professor Richard Muller and Robert Rohde also from the Berkeley campus. They studied the disappearances of thousands of different marine species (whose fossils are better preserved than terrestrial species) over the past 500m years.

Their results were completely unexpected. It was known that mass extinctions have occurred in the past. During the Permian extinction, 250m years ago, more than 70 per cent of all species were wiped out, for example. But most research suggested that these were linked to asteroid collisions and other random events.

But Muller and Rohde found that, far from being unpredictable, mass extinctions occur every 62m years, a pattern that is 'striking and compelling', according to Kirchner.

But what is responsible? Here, researchers ran into problems. They considered the passage of the solar system through gas clouds that permeate the galaxy. These clouds could trigger climatic mayhem. However, there is no known mechanism to explain why the passage might occur only every 62m years.

Alternatively, the Sun may possess an undiscovered companion star. It could approach the Sun every 62m years, dislodging comets from the outer solar system and propelling them towards Earth. Such a companion star has never been observed, however, and in any case such a lengthy orbit would be unstable, Muller says.

Or perhaps some internal geophysical cycle triggers massive volcanic activity every 62m years, Muller and Rohde wondered. Plumes from these would surround the planet and lead to a devastating drop in temperature that would freeze most creatures to death.

Unfortunately, scientists know of no such geological cycle.

'We have tried everything we can think of to find an explanation for these weird cycles of biodiversity and extinction,' Muller said. 'So far we have failed. And, yes, we are due one soon, but I would not panic yet.'

Source
 
Emperor said:
Bad news - we are way past our 'extinct by' date

...
But Muller and Rohde found that, far from being unpredictable, mass extinctions occur every 62m years, a pattern that is 'striking and compelling', according to Kirchner.
...

Most especially when you are living through it! :roll:

That 62 my pattern has always bothered me. What exactly occurs every 62 my? :?
 
Just looked at the data. While I know the fossil record is patchy and that dating techniques ropey but I'm just not convinced by a quick visual inspection. There are at least two "double whammy" events and the sudden mass extinction event that took place 124my ago seems to have been a sudden decline at 140my ago followed by 25my of bouncing along the bottom. There are also two very distinct events at 250mya and 200mya. At the dinosaur event the number of species declined to a low with the level of the post 250my event high.

I somehow think they have not taken all sources of error into their calculation. Could of course just be a "big media story" before a grant application. I'm always suspicious of off-field scientists spotting something those in the field just "didn't notice".
 
Sea life 'killed by exploding star'

Alok Jha, science correspondent
Monday April 11, 2005
The Guardian

A huge blast of radiation from an exploding star might have been behind one of the Earth's worst mass extinctions, some 450m years ago.

In the latest issue of the Astrophysical Journal Letters, scientists argue that a gamma ray burst, the most powerful explosion that occurs in the universe, was responsible for the Ordovican mass extinction in which 60% of all marine invertebrates died.

Gamma ray bursts are thought to be caused either when two neutron stars collide or when giant stars collapse into black holes at the end of their lives.

Article continues
For around 10 seconds, intense pulses of energy are fired off, which can be detected right across the universe. All the bursts recorded by astronomers so far have come from distant galaxies and are therefore harmless to the Earth.

But if a burst occurred in our own galaxy, the effect would be devastating.

Dr Adrian Melott, of the University of Kansas and an author of the latest paper, said: "A gamma ray burst originating within 6,000 light years from Earth would have a devastating effect on life.

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

Such a burst would strip the Earth of its protective ozone layer, allowing deadly ultraviolet radiation to pour down from the sun.

Computer models showed that up to half the ozone layer could be destroyed within weeks. Five years later, at least 10% would still be missing.

Using computer models, the researchers calculated that plankton and other life in the first few feet of the oceans would have been destroyed.

The knock-on effect would have been huge: plankton are at the bottom of the marine food chain providing for animals which are then preyed upon by larger species.

Previously, scientists thought that an ice age caused the Ordovican extinction. A gamma ray burst would have had a similar effect, causing a fast die-off early on and triggering a significant drop in surface temperature.

Astronomers are planning to launch a robot spacecraft to study the mysterious gamma ray bursts further.

Because the bursts happen suddenly and are so short, scientists have been lucky to detect one a month with instruments on Earth.

Next month, Nasa will launch the £138m Swift probe, which will sweep up to one sixth of the sky at a time, looking for sudden bursts. If all goes well, the probe could catch two three explosions a week.

http://www.guardian.co.uk/uk_news/story ... 94,00.html
 
Another report on this:

Ray burst is extinction suspect

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.

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.
------------------------
Story from BBC NEWS:
http://news.bbc.co.uk/go/pr/fr/-/1/hi/s ... 433963.stm
Published: 2005/04/11 18:30:40 GMT
© BBC MMV
 
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Poisonous volcanic gas caused world's largest mass extinction, study

The research, published in the journal Geology, reveals vital clues about the mass extinction at the end of the Permian period, 250 million years ago, when mammal-like reptiles known as synapsids roamed the earth. Many scientists had previously thought that an asteroid hitting the earth or a deep-sea methane release had caused the extinction, which obliterated more than two-thirds of reptile and amphibian families.

However, analysis of a unique set of molecules found in rocks taken from the Dolomites in Italy has enabled scientists to build up a picture of what actually happened. The molecules are the remains of polysaccharides, large sugar-based structures common in plants and soil, and they tell the story of the extinction.

The molecules date from the same time as a major volcanic eruption that caused the greatest ever outpouring of basalt lava over vast swathes of land in present day Siberia.

The researchers believe that the volcanic gases from the eruption, which would have depleted earth's protective ozone layer and acidified the land and sea, killed rooted vegetation. This meant that soil was no longer retained and it washed into the surrounding oceans.

The chemistry of the rocks reveals that although the sugar molecules were found in marine sediments, they derived from land, supporting the theory that massive soil erosion caused them to end up in the sea.

Soil materials in the oceans would have blocked out light and soaked up oxygen. Analysis of rock chemistry suggests that after the soil crisis on land, the marine ecosystem succumbed to the stresses of environmental change and oceanic life faltered, completing a global catastrophe.

Dr Mark Sephton, from Imperial College London's Department of Earth Sciences and Engineering and lead author of the research, said: "The cause of the end Permian extinction has been highly controversial. We show that the terrestrial ecosystem was the first to suffer. The continent-wide nature of the event implies that it was caused by something in the atmosphere. The unique chemical data indicates that something fast and catastrophic happened on land."

Prof Henk Visscher of Utrecht University, also part of the research team, commented: "Similar to the 'Dead Zone' nowadays spreading in the Gulf of Mexico, the soil crisis could have caused a worldwide expanse of uninhabitable low-oxygen conditions in shallow marine waters. So what began on land ended in the sea. It seems there was no place to hide at this time of great dying."

Dr Sephton believes that lessons can be learned in the present day from the damage caused by the end Permian extinction: "Land degradation is a worsening global problem thanks to human activity and soil erosion has caused the loss of a third of arable land over the last forty years. 35% of the Earth's land is now soil-free. Identifying the nature of the end Permian soil crisis may help us understand what is in store for us in the years ahead," he said.

The research was carried out by an international team of scientists from the United Kingdom, the Netherlands and the United States.

Source: Imperial College London
http://www.physorg.com/news8673.html
 
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A Lag Before Dying
By Krista Zala
ScienceNOW Daily News
12 March 2007

As recent geologic events go, few had more dramatic consequences than the formation of a land bridge between Central and South America 3 million years ago. Formed by the Pacific tectonic plate sliding under the Caribbean one, the Isthmus of Panama divided the Atlantic and Pacific oceans, radically altering sea currents. A massive extinction of marine animals ensued, yet death may not have come quickly. According to a new study, the rate of these extinctions peaked about 2 million years after the Isthmus formed. The discovery complicates the tidy notion of an ecological change rapidly following an environmental one.
Before the Isthmus of Panama emerged, the open waters between North and South America were similar to the Pacific today. Both were muddy, loaded with plankton, and nourished by nutrient-rich waters that regularly rose from the depths. Once the Isthmus split the sea into the Caribbean and the Pacific, upwelling in the Caribbean stopped. The region's plankton starved, but its reef-building corals thrived. And, traditional theory goes, animals that loved the upwelling died out in their new environment within the geologically instantaneous time frame of thousands of years.

Not so fast, says marine paleontologist Aaron O'Dea, of the Smithsonian Tropical Research Institute in Balboa, Panama. He and colleagues tracked shifts in ancient ecosystems by counting the overall abundance of marine invertebrate fossils and analyzing how populations of species swelled or shrank over time. Reporting online this week in Proceedings of the National Academy of Sciences, O'Dea and colleagues conclude that after the Caribbean shifted from the Pacific to its present-day environment, many species that loved the old conditions managed to cling to life for as long as 2 million years before biting the dust. O'Dea says that these communities may have remained steady under deteriorating conditions until they reached a critical level, then collapsed. Extinction rates in the Caribbean peaked in the last 1 million to 2 million years, the team reports, with half the solitary, mud-loving coral species and a third of mollusk species dying out every million years.

The study "points out something we haven't noticed before: the time lag between environmental shifts ... and a peak in the extinction," says Peter Roopnarine, an invertebrate zoologist at California Academy of Sciences in San Francisco. Evolutionary biologist David Jablonski of the University of Chicago in Illinois says that the extinction delay is perhaps not surprising, given that hardier members of a species might be able to stick things out longer than the species as a whole. Whatever the cause, O'Dea says, the findings could mean that other "quick" extinctions may not have been so rapid after all.
http://sciencenow.sciencemag.org/cgi/co ... 2007/312/3
 
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Mighty_Emperor linked:
Or perhaps there's some kind of "natural timetable" deep inside the Earth that triggers cycles of massive volcanism, Rohde has thought. There's even a bit of evidence: A huge slab of volcanic basalt known as the Deccan Traps in India has been dated to 65 million years ago -- just when the dinosaurs died, he noted. And the similar basaltic Siberian Traps were formed by volcanism about 250 million years ago, at the end of the Permian period, when the greatest of all mass extinctions drove more than 70 percent of all the world's marine life to death, Rohde said.
Hi Emps
I almost missed this one.
Someone has pointed out, and I can't remember who, that the Deccan Traps lie on a line on almost the opposite side of the globe as the Chicxulub Crater and are dated at the same time.
 
Intetrestingly enough, the Tharsis volcanoes on Mars are more or less opposite the giant Hellas impact crater. The connection between impact and volcanism isn't proved or otherwise at the moment.
 
Mammal rise 'not linked' to dinos
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The extinction of the dinosaurs 65 million years ago had little effect on the evolution of mammals, according to a study in the journal Nature.
One theory had suggested the rise of the mammals was directly linked to the disappearance of the dinosaurs.

The evidence challenging the connection comes from the most complete family tree compiled for mammals.

It shows how different groups, such as primates and rodents, are related and when they diverged.

An international team compiled the mammal "supertree" from existing fossil data and from genetic analyses.

Throughout the Cretaceous Period, when dinosaurs walked the Earth, mammals were relatively few in number, and were prevented from diversifying and evolving in ecosystems dominated by the ancient reptiles.

Explosive evolution

According to the established view, the extinction of the dinosaurs removed this constraint, allowing mammals to diversify and flourish, and placing them on course to their present position of dominance on Earth.

Under this model, placental mammals split into major sub-groupings, which originated and rapidly diversified after the mass extinction event - thought to have been caused by an asteroid or comet striking Earth 65 million years ago (a point in time recorded in rocks and referred to by geologists as the K-T boundary).

Co-author Kate Jones, from the Zoological Society of London, told the BBC Radio 4's Leading Edge programme: "The meteor impact that killed off the dinosaurs has traditionally been thought to have given mammals the edge they needed."


Some mammals did benefit from the demise of the dinosaurs


More details

However, the supertree shows that the placental mammals had already split into these sub-groups by 93 million years ago, long before the space impact and at a time when dinosaurs still ruled the planet.

After the origin of these sub-groups - or orders - the rate of mammal evolution fell and remained low again until the Eocene Epoch, 55 million years ago.

The start of the Eocene was marked by rapid global warming and an explosion in the diversity of mammal lineages.

"The [supertree] is a new way of showing all the mammal species on the planet, starting with a common ancestor. Species relationships can be inferred from morphological characteristics and genetic sequences," explained Dr Jones.

"If we had done this from scratch, we would have had to get molecular and morphological data for 4,000 different species.

"What we did instead was use already published information from hundreds of researchers around the world. We used a new technique called supertree construction which allows us to get all the information that's out there, re-code it and re-analyse it as if it's all part of one dataset."

'Straw man' theory

The composition of rocks and marine sediments laid down at the boundary between the Palaeocene and Eocene epochs show that global temperatures rose by around six degrees Celsius in less than 1,000 years - an event known as the thermal maximum.

Dr Rob Asher, an expert on mammalian phylogeny at the University of Cambridge, said: "Palaeontologists have known for over a hundred years that not all modern placental mammal groups appear right after the K-T boundary.

"Most orders of placental mammals - what I mean by that is cats and bats and whales and people - appear at the Eocene. On the flipside, not all dinosaurs disappear at the end of the Cretaceous.

"There was a period of several million years at the end of this period which witnessed several extinctions of non-avian dinosaurs. So the old textbook idea that at the K-T boundary dinosaurs disappeared and mammals appeared is a bit of a straw man."

But the idea that mammal fossils from the Cretaceous represent ones ancestral to today's mammals was a controversial question, said Dr Asher.
http://news.bbc.co.uk/2/hi/science/nature/6503045.stm
 
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