Posted on 01/29/2002 8:41:57 AM PST by RightWhale
http://www.spaceref.com/news/viewpr.html?pid=7246
PRESS RELEASE
Date Released: Monday, January 28, 2002
Marshall Space Flight Center
The Great Dying 250 Million Years Ago
250 million years ago something unknown wiped out most life on our planet. Now scientists are finding buried clues to the mystery inside tiny capsules of cosmic gas.
January 28, 2002: It was almost the perfect crime.
Some perpetrator -- or perpetrators -- committed murder on a scale unequaled in the history of the world. They left few clues to their identity, and they buried all the evidence under layers and layers of earth.
The case has gone unsolved for years -- 250 million years, that is.
But now the pieces are starting to come together, thanks to a team of NASA-funded sleuths who have found the "fingerprints" of the villain, or at least of one of the accomplices
Above: Life was flourishing on the Earth about 250 million years ago, then during a brief window of geologic time nearly all of it was wiped out. This image is an artist's impression of a Lower Permian swamp in Texas.
The terrible event had been lost in the amnesia of time for eons. It was only recently that paleontologists, like hikers stumbling upon an unmarked grave in the woods, noticed a startling pattern in the fossil record: Below a certain point in the accumulated layers of earth, the rock shows signs of an ancient world teeming with life. In more recent layers just above that point, signs of life all but vanish.
Somehow, most of the life on Earth perished in a brief moment of geologic time roughly 250 million years ago. Scientists call it the Permian-Triassic extinction or "the Great Dying" -- not to be confused with the better-known Cretaceous-Tertiary extinction that signaled the end of the dinosaurs 65 million years ago. Whatever happened during the Permian-Triassic period was much worse: No class of life was spared from the devastation. Trees, plants, lizards, proto-mammals, insects, fish, mollusks, and microbes -- all were nearly wiped out. Roughly 9 in 10 marine species and 7 in 10 land species vanished. Life on our planet almost came to an end.
Scientists have suggested many possible causes for the Great Dying: severe volcanism, a nearby supernova, environmental changes wrought by the formation of a super-continent, the devastating impact of a large asteroid -- or some combination of these. Proving which theory is correct has been difficult. The trail has grown cold over the last quarter billion years; much of the evidence has been destroyed.
"These rocks have been through a lot, geologically speaking, and a lot of times they don't preserve the (extinction) boundary very well," says Luann Becker, a geologist at the University of California, Santa Barbara. Indeed, there are few 250 million-year-old rocks left on Earth. Most have been recycled by our planet's tectonic activity.
Undaunted, Becker led a NASA-funded science team to sites in Hungary, Japan and China where such rocks still exist and have been exposed. There they found telltale signs of a collision between our planet and an asteroid 6 to 12 km across -- in other words, as big or bigger than Mt. Everest.
Many paleontologists have been skeptical of the theory that an asteroid caused the extinction. Early studies of the fossil record suggested that the die-out happened gradually over millions of years -- not suddenly like an impact event. But as their methods for dating the disappearance of species has improved, estimates of its duration have shrunk from millions of years to between 8,000 and 100,000 years. That's a blink of the eye in geological terms.
"I think paleontologists are now coming full circle and leading the way, saying that the extinction was extremely abrupt," Becker notes. "Life vanished quickly on the scale of geologic time, and it takes something catastrophic to do that."
Such evidence is merely circumstantial -- it doesn't actually prove anything. Becker's evidence, however, is more direct and persuasive:
Deep inside Permian-Triassic rocks, Becker's team found soccer ball-shaped molecules called "fullerenes" (or "buckyballs") with traces of helium and argon gas trapped inside. The fullerenes held an unusual number of 3He and 36Ar atoms -- isotopes that are more common in space than on Earth. Something, like a comet or an asteroid, must have brought the fullerenes to our planet.
Becker's team had previously found such gas-bearing buckyballs in rock layers associated with two known impact events: the 65 million-year-old Cretaceous-Tertiary impact and the 1.8 billion-year-old Sudbury impact crater in Ontario, Canada. They also found fullerenes containing similar gases in some meteorites. Taken together, these clues make a compelling case that a space rock struck the Earth at the time of the Great Dying.
But was an asteroid the killer, or merely an accomplice?
Many scientists believe that life was already struggling when the putative space rock arrived. Our planet was in the throes of severe volcanism. In a region that is now called Siberia, 1.5 million cubic kilometers of lava flowed from an awesome fissure in the crust. (For comparison, Mt. St. Helens unleashed about one cubic kilometer of lava in 1980.) Such an eruption would have scorched vast expanses of land, clouded the atmosphere with dust, and released climate-altering greenhouse gases.
World geography was also changing then. Plate tectonics pushed the continents together to form the super-continent Pangea and the super-ocean Panthalassa. Weather patterns and ocean currents shifted, many coastlines and their shallow marine ecosystems vanished, sea levels dropped.
"If life suddenly has all these different things happen to it," Becker says, "and then you slam it with a rock the size of Mt. Everest -- boy! That's just really bad luck."
Was the "crime" then merely an accident? Perhaps so. Nevertheless, it's wise to identify the suspects -- an ongoing process -- before it happens again.
I've often speculated such was the case. It might be fruitful for experts to investigate why Pangaea started to break up after what appears to be a long period of equilibrium. I wonder a lot, as well, about what kinds of events were involved in bringing deep plutonic rocks like Kimberlites to the surface in Africa, Siberia, Canada, Australia and other regions where diamond "pipes" are found. Could they have been the result of powerful impact events?
The theory of Pangea is interesting but I would like to hear more of how a single continent originally formed or split and reformed to a single continent again. Some of these theories move continents around to fit the "disaster d'jour".
Pangaea broke up because it had been together quite long enough and it was all a big mistake to begin with, thank you very much.
:-)
I wonder a lot, as well, about what kinds of events were involved in bringing deep plutonic rocks like Kimberlites to the surface in Africa, Siberia, Canada, Australia and other regions where diamond "pipes" are found. Could they have been the result of powerful impact events?
No. Kimberlites are diatremes, which are caused by violent, volatile-rich eruptions from the deep mantle (hence, the diamonds, which require very high pressures to crystallize). Impacts, even the very largest events, only affect the upper few kilometers of planetary crusts.
Who got the ring? Very funny response but it doesn't help much with my question.
Kimberlites are diatremes, which are caused by violent, volatile-rich eruptions from the deep mantle
Can you point me in the direction of books/info on diatreme eruptions and their cause? (I'll Google as soon as I finish this message). They seem to be very ancient events, but possibly violent enough in themselves to have influenced earth's biology if any occurred within the time life has been evolving.
I wonder if this will blow in the next 50 years.
Cheers.
As for kimberlites, there is a large, professional literature. The best reference is:
Wylie P.J. (1967) Kimberlites, in Ultramafic and Related Rocks, J. Wiley and Sons, New York, pp. 240-278.
Good luck!
Thanks very much for taking the time to post a reference. I'll definitely try to find it. Meanwhile, I've found a lot of interesting stuff on-line.
Yes, convection is pretty interesting. I melt quite a bit of gold and silver for casting jewelry and have always thought the "scum" on the surface of the melt is a fair analog for what's happening to the continents on earth's molten core (enormous differences, of course, but an analog as I said). The movement of the surface scum on molten metal seems to be related to the direction of heat application and the total amount of heat. Those two factors are probably the major ones in plate tectonics (apart from earth's rotational effects, gravitational forces, the presence of immense quantities of liquid water, etc., etc.) It still seems plausible that impacts may play some role from time to time.
And ROACHES! Oh excuse me, you Florida residents, palmetto bugs! LOL!
Then please explain the relevance of this statement from the article.---
Indeed, there are few 250 million-year-old rocks left on Earth. Most have been recycled by our planet's tectonic activity.
You need rocks to date them. You need dated rocks to rate the accuracy of the method. And you need a standard. Now you may be very precise, but very inaccurate.
This is like the association between the K/T impact and the formation of the Deccan Traps (Asia) at approximately the same time and again an impact has been indicated as a possible cause of the formation of Basalts in SE Oregon and Idaho about 17mya (starting point of Yellowstone hot spot).
Direct impacts causing volcanism "Impact Volcanism" would probably mask the impact craters in basalt and 250my can hide a lot of stuff.
A direct impact may not be necessary to cause volcanism, but the shock waves of a large impact may reinforce each other at a position globally opposite the impact site (antipode) which, taking into account the positions of the continents 65mya, seems to have happened at the K/T boundary.
Around 1980, after suffering three >6.0 magnitude earthquakes in quick succession, the USGS was very concerned that something was going on. The CO2 emissions, dome building and earthquake swarms triggered at that time are continuing.
I would say Yellowstone is a bigger danger at this time.
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Hunt for Oil Leads to Crater Linked to 'Great Dying'The team, led by geologist Luann Becker of the University of California, Santa Barbara examined undersea drilling samples taken by oil prospectors in the 1970s and '80s and since held in an Australian lab. They also studied ancient layers of Earth now exposed on land Down Under and in Antarctica. Dated to the time of the mass extinction, they found breccia, a porous rock often linked to impacts. And they uncovered tiny glass beads and material known as shocked quartz, which has been fractured in several directions. These can be indicators of the extreme heat generated when a large, high-speed extraterrestrial object slams into the planet... The findings point to the existence of a 125-mile-wide (200-kilometer) crater called Bedout off the northwest coast of Australia. The ring-like structure had previously been identified as a possible impact crater by seismic data and a map of gravity variations in the area.
by Robert Roy Britt
13 May 2004
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Well duh, so Alaska could have a State Bird...
Not just any roach can be a Palmetto Bug, only the ones bigger than 1-1/2 inches.
Ok heres what you want to know.
Ill try to keep it short. When heavy planets form initially they heat up. and are molten. than as they start to form a atmosphere the surfaced start to cold and form a think layer of mass, which over time condensates to a local point do to rotation of the planet( Pangaea) the subsurface layer( under the liquid, typically water based, forms a solid crust. This a common scenario fyi and and about 85 percent of starts have planets and about 1 in 1000 stars have some from of live. Now what happened here is that a very large meteor pinged earth like a pool ball, near what was than northern africa roughly, according to most maps, and fractured the crust like a egg shell, this is also very common occurance over such a long period of time. hence the creation of the plates, what happens that causes great extinctions in life forms is, as the fractures occur you get massive volcanic activity all at the the same time along the fractured plate boundrys, which causes a number of effectss, the 2 primary being poisonous gases and atmospheric changes in content and Temperature, which tends to crush most forms of life, much of what goes extinct depends on the type and severity of the effects and somewhat on geological locations etc etc etc you can figure the rest ,,it can actually be modeled. if your understanding/science is great enough. please forgive the bad grammer and this is a summary fyi and not complete detail..didnt fell like typing to much or editing to much :) Im tired and its late
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