250 million year old mass extinction crater?

[Brian G Turner]

US geologists claim to have identified a suspect in the Earth's largest and most mysterious mass extinction - a large impact crater off the coast of Australia. However, other geologists are not convinced that the "smoking gun" is even a gun, let alone the lethal weapon.

Luann Becker, of the University of California at Santa Barbara, and colleagues present data in the journal Science that they says reveals a crater rivalling the one blamed for killing the dinosaurs. They say the effects of the newly revealed impact would have devastated the planet 250 million years ago at the end of the Permian period.

Paleontologists have long puzzled over the Permian mass extinction, which killed over 90 per cent of marine species and 50 to 70 per cent of land animals. The discovery of the Chicxulub impact structure in Mexico indicated that a 10-kilometre asteroid wiped out the dinosaurs 65 million years ago and put impacts at the top of the suspect list for the Permian event.

But key evidence was missing, including the iridium-rich fingerprints of an asteroid in sediments and an impact crater. Many researchers came to suspect the gas and dust from massive volcanic eruptions in Siberia were to blame.


More: http://www.newscientist.com/news/news.jsp?id=ns99994993

 

[Brian G Turner]

Personal comment - all this search for impacts, IMO, is completely missing the point, the Chicxulub crater simply isn't large enough by itself to create the long-term affects required to cause the mass extenction believed occuring. So the Australian one - if responsible for a far larger mass-extinction - absolutely needs something extra to lend any credance that this may be involved.

I'm sure it was Survivor who pointed out on another thread that the impact craters being pinpointed could simply have been the larger part of a larger fragmenting body. HOWEVER, in my opinion, if a research team is going to try and claim that a specific event has a specific single cause, then it absolutely must be able to account for that event fully. Lots of smaller fragments hitting the earth just isn;t going to cause a mass-extinction event by the explanations forwarded - so if someone is going to claim that a single impact caused such mass extinctions then they absolutely have to be able to explain demonstrably why such a crater impact would have caused such a mass exincttion, rather than claiming for such a loose casual - and unexplained - association between the two.

 

[kyektulu]

I will have to give this more thought before commenting.

 

[PERCON]

Could it be possible though that over a million years for example, the smaller and seemingly faster prey just out ran and out lived the bigger predators, a case of the survival of the fittest really. The dinosaurs will have died out around the same time as the prey had evolved to evade them thus making it look as though an impact wiped them out.

I've never really accepted the 'big meteor impact theory' as the reason for the extinction of the dinosaurs. Personally, I think a more evolution-based scenario may be needed and may be a more valid theory. I may be wrong, I may be right but that's not what matters. Finding the truth is all that matters.

Has anyone else got a different theory, if so I'd love to hear it...

PERCON - "I'm not deranged, just different..."

 

[Stalker]

But impact with the meteor even with diameter about a mile will suffice to annihillate all big life forms. Anly a small carrion-eater could survive in condition of nuclear winter that surely ould have followed. And it surely followed, you may not even doubt that!
The formula is simple - remember your school textbooks on physics. mv2/2
The specific density of a rock (in meteor it would largely be composed of nickel or zink) may vary but will hardly be less that 3000 kg/m3.
Let's take the radius of a meteor as 800 m. The volume of the sphere will roughly be V= 3/4 pi R3 So, V then will be equal to 3/4 X 3,1415 X 800 (3) = 1,206,336,000 m3. The mass of a meteor will be equal then to 1,206,336,000 X 3000 = 3,619,008,000,000 kg or 3,619,008,000 tons. The angular speed of the meteor correlated with Earth's speed may reach 50 km/sec. It will be 5000 m/sec in Ci units. All right putting that all into the formula: 3,619,008,000,000 X 5000 (2)/ 2 = 452,376,000,000,000,000,000 joules or 4,52376 X 1020 Joules.
That's of course, a rough calculation but it gives you an idea of the energy that blows up when such a meteor stirkes Earth.
Hiroshima bomb released the energy egual 8.370 x 1013 Joules that is roughly 5,000,000 times as less! Think of what horror could such a small rock cause!

 

[Brian G Turner]

But impact with the meteor even with diameter about a mile will suffice to annihillate all big life forms. Anly a small carrion-eater could survive in condition of nuclear winter that surely ould have followed.

I'm under the impression that no calculation so far can create dynamics that will result in a nuclear winter effect from the impact that caused the Chicxulub crater. Therefore to imply a nuclear winter from it would require a magic "unknown" to create an effect to tally with the impact hypothesis. As this would be obviously unacceptable, then the hypothesis would be wrong if the objection sustained.

It's also worth pointing out that the dinosauria included carrion feeders, but plenty of herbivore and carnivore non-dinosaur species survived.

The impact hypothesis certainly creates a significant event, but it's not enough to create complete extinction of all dinosaur species while leaving other groups damaged but surviving.

2c.

 

[polymorphikos]

What about the theory in Walking With Dinosaurs - that the saurians were already at a fragile point and the meteorite tipped them over.

However, considering the close intersection of times and the absolute dominance of the dinosaurs prior to the impact, followed by a highly-apparent opposite, the meteor probably had something to do with it. Perhaps it created an untenable situation, as opposed to a total nuclear winter. I don't know. I'm not a geologist/astrophysicist/at all knowledgeable on the topic.

 

[dreamwalker]

Alot suggest that the Permian Mass extinction had something to do with a Super Volcano/Caldera

The occurrence of a super-eruption would have severe environmental effects and might threaten global civilisation. This is the assessment of a Geological Society of London working group composed of senior Earth Scientists. The effects of a super-eruption would be comparable to those predicted for the impact of a 1km-diameter asteroid with the Earth. In fact, super-eruptions are 5-10 times more likely to occur than such an impact.

http://www.solcomhouse.com/yellowstone.htm
"Back in the day" an eruption of this magnatide could have gone on for months, even years... easily enough to cause the Permain mass extinction.

Alot of what happened with the other impact new mexico is to do with fluidisation...

A comet or asteroid the size of a small city rocked the planet, sending giant tsunamis across the ocean and earthquakes reverberating around the globe. It also turned much of the Yucatan into mush, scientists suspect, causing rock to behave like a thick fluid.

http://www.space.com/scienceastronomy/planetearth/asteroid_jello_001122.html
Apparently, because of the central uplift (see http://www.space.com/images/h_chicxulub_anim_02.gif ) failling back down to earth, It was the eqivilant of having 2 impacts

 

[Stalker]

It's also worth pointing out that the dinosauria included carrion feeders, but plenty of herbivore and carnivore non-dinosaur species survived.

With all due respect, Brian, it's not the fact! In condition when the light of the sun cannot penetrate the clouds of dust in the atmosphere, the plants will sffer first. Then it's herbivors' turn to die. Etc. Simple feeding chain. Still, paleontologists simply cannot give well-defined answer to that question.
You may stick to any other theory explaining mass extinction (that took place regularly, each 200 million years) but the main cause of it would still be braking the climatic balance due to dramatic and abrupt chanches that had taken place. By the way, in chalk layers (65 million years ago) paleontologists find the traces of huge fires all over the Earth. What does it tell us?
All right, to those sticking to volcano theory...
The explosion of a Santorini volcano had effect not only on Minoyan civilisation - the Cinese far far East noticed clouds of dust and ashes hiding sun from them! After Krakatoa's eruption on the island Java in august 1883 over 19 km3 of ashes was blon into the air, and that caused lovages during a few years thereafter and average global cooling 1-1,5 degrees centigrade.
Whatever you say, volcano or meteor - the effect would be the same - "nuclear" winter. Chicsxulub crater is 145-180 km that's means that rock that hit Earth was no less than 3 miles (at least 4 times as more as what I calculated). How much dust and ash will it raise to the atomosphere?
"It's what we call a global killer,.. sir!"

 

[Brian G Turner]

I still think there's too much simplification in looking for a single cause, when IMO there's definitely call for multiple causes to be involved - for example, in the Cretaceous extinction we also have the Deccan Traps in India basically turning that subcontinent into one huge eruption.

I've also seen arguments from the fossil record that although there is a clearly marked K-T boundary, we still have dinosaurs in existence over the following 5 million years, slowly dying out.

Yes, a nuclear winter scenario is going to be a catastrophic global event - but I simply don't see this scenario scientifically sustained - as before, the mechanics of the Chicxulub impact apparently will not lead to the creation of a nuclear winter scenario, and so the proponents of that hypothesis claimed instead that the meteorite must have happened to hit an unusual type of rock that would have caused the event - in other words, the meteorite itself could not cause the proposed level of destruction, so it was claimed that it hit "magic rock" that happened to cause especially devastating climatic effects in an impact.

Again, the point of the objection is that I've not seen Chicxulub argued as having sufficient mechanical energy to cause an actual nuclear winter effect. A huge energy impact, yes, but not a global killer.

We can see from the geological record that there was at least one large meteorite strike, and there was also massive volcanic activity - BUT the geological record also apparently shows no sudden mass extinction, but a gradual one.

It's also worth pointing out that the most devastating effects of such an impact would have been across North America, which I have to admit sometimes seems to come across as a particular bias in North American researchers - if the dinosaur record in Colorado shows sudden devastation, then they apply that globally without apparently justifying why.

Overall, I think there's far too much simplification in the Cretaceous event - I really don't think we're looking at a single cause, but instead, multiple causes all having an effect over an extended period, which doesn't cause a nuclear winter event, but would cause widespread climatic changes then over an extended time would result in heavy extinction pressures on the majority of the ecological systems of earth at the time.

But...that's just my personal 2c.

 

[Stalker]

Well, it we take as proven fact that the extinction time lengthened out over millions of years, then meteor theory shall sound bancrupt. And then, you are absolutely right, my dear friend.
Nonetheless, I will argue only one point of yours that is that 3-mile meteor (Chicxulub impact case) could not have been global killer. Roughly speaking it was as good ad 20 million Hiroshimas! You only think what energy is that! No "magic rock" is needed - simple physics! Impact, earthquakes, devastating tsunamies wiping out all continental shorelines thousand miles deep... If miserable (in comparison!) Krakatoa erupted with over 19 km3 of ashes blown into the air and the whole world felt that, so how much dust and ashes would have been blown up to the atmosphere at the Chicxulub impact?
In recent Roland Emmerich's movie, the so called "domino" effect of abrupt climatic change is shown perfectly clear. Hope, you will not argue that all things are interrelated in thes best of the worlds? One small change may cause the chain reaction of other changes...

 

[Brian G Turner]

Nonetheless, I will argue only one point of yours that is that 3-mile meteor (Chicxulub impact case) could not have been global killer. Roughly speaking it was as good ad 20 million Hiroshimas! You only think what energy is that! No "magic rock" is needed - simple physics! Impact, earthquakes, devastating tsunamies wiping out all continental shorelines thousand miles deep...

I'm thinking particularly on how the debate raged in the 1990's, and how Scientific American covered the argument, not least after Chicxulub was analysed - and that's when it was postulated that the energy released would in fact have been incapable of causing the previously ascribed climatic event, and that's why the actual type of rock impacted would have been the actual key to the extinction event - - - and this was all from the pro-impact arguments.

This is a subject I definitely need to return to and collect references on, not least to see how the current arguments are running - but it's still a fun subject to discuss.

 

[dreamwalker]

I'm thinking particularly on how the debate raged in the 1990's, and how Scientific American covered the argument, not least after Chicxulub was analysed - and that's when it was postulated that the energy released would in fact have been incapable of causing the previously ascribed climatic event, and that's why the actual type of rock impacted would have been the actual key to the extinction event - - - and this was all from the pro-impact arguments.

This is a subject I definitely need to return to and collect references on, not least to see how the current arguments are running - but it's still a fun subject to discuss.

Just on a side note...
It was suggested that the Chicxulub impact actually slowed down the length of a day by almost a minute. Maybe this accounted for the mass extinction

 

[chrispenycate]

The extraordinary detail for me was the "killed over 90 per cent of marine species and 50 to 70 per cent of land animals" What conceivable catastrophe could kill that high a percentage of marine life (thermally blanketed, capable of migrating or being migrated when conditions change, shock mounted) without anihilating the dry land species (and what were the dry land species at that time? I suppose I'm going to have to do some research to do a reasonable theory) Poisoning? But surely a cyanide comet crashing into the sea woul poison the atmosphere pretty conclusively too, and ocean currents are unreliable enough that it would need some pretty impressive fragmentation to get that high a death toll.

As regards the energy calculations- why assume the cosmic body was metallic? The reason most meteorites that reach earth are metallic is that most of the other junk falling on us vaporises before getting down- but with a big enough lump you could make it out of cheese and you'd still get enough impacting to make a heck of a fondue.

If birds survived, and crocodiles survived,(oh, and mammals too, but they're not over important- not like say cockroaches) when dinosaurs of a wide range of shapes and sizes disappeared the "nuclear winter" type explanation needs a lot of jiggery pokery- I almost prefer the death rays from the black hole at the center of the galaxy.