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Posted on 02/05/2010 7:31:57 AM PST by Palter
Double impact may have caused tsunami, global cooling
Pieces of a giant asteroid or comet that broke apart over Earth may have crashed off Australia about 1,500 years ago, says a scientist who has found evidence of the possible impact craters.
Satellite measurements of the Gulf of Carpentaria (see map) revealed tiny changes in sea level that are signs of impact craters on the seabed below, according to new research by marine geophysicist Dallas Abbott.
Based on the satellite data, one crater should be about 11 miles (18 kilometers) wide, while the other should be 7.4 miles (12 kilometers) wide.
For years Abbott, of Columbia University's Lamont-Doherty Earth Observatory, has argued that V-shaped sand dunes along the gulf coast are evidence of a tsunami triggered by an impact.
"These dunes are like arrows that point toward their source," Abbott said. In this case, the dunes converge on a single point in the gulf—the same spot where Abbott found the two sea-surface depressions.
The new work is the latest among several clues linking a major impact event to an episode of global cooling that affected crop harvests from A.D. 536 to 545, Abbott contends.
According to the theory, material thrown high into the atmosphere by the Carpentaria strike probably triggered the cooling, which has been pinpointed in tree-ring data from Asia and Europe.
What's more, around the same time the Roman Empire was falling apart in Europe, Aborigines in Australia may have witnessed and recorded the double impact, she said.
Aborigine Eyewitnesses
Based on the new research, Abbott thinks the two craters were made by an object that split into pieces as it approached Earth.
To make a pair of craters this big in the seafloor's soft sediments, the original object must have been about 2,000 feet (600 meters) across before it broke up, she said.
Core samples from the region back up the case for such an impact, Abbott added. Previous research had found that the samples contain smooth, magnetic spherules, which were probably created when the object's explosive landing melted material and blasted it into the sky.
Furthermore, a 2004 paper in the journal Astronomy and Geophysics suggested that the circa-A.D. 500 global cooling event might have been caused by dust from an impact of approximately the size Abbott has now calculated for Carpentaria.
It's even possible the impact had eyewitnesses: Aboriginal rock art from the region seems to have recorded the event, although the researchers examining this art declined to discuss details until after their paper has been published.
Still, Duane Hamacher, a Ph.D. student at Macquarie University in Sydney not involved with the rock-art work, recently demonstrated that Aboriginal stories can be used to locate meteorite craters.
"Numerous examples of fiery stars falling from the sky and striking the earth, causing death and destruction, are found throughout Aboriginal Dreamings [spiritual folk stories] across Australia," Hamacher wrote on his blog.
"The descriptions seem to indicate that the events were witnessed, not simply 'made-up.'"
In findings yet to be published, Hamacher used one set of Aboriginal stories, along with images in Google Earth, to locate a 919-foot-wide (280-meter-wide) impact crater in Palm Valley, in Australia's Northern Territory.
Too Many Meteorite Strikes?
But some experts are skeptical of Abbott's conclusions, which were presented last December at a meeting of the American Geophysical Union in San Francisco.
One potential problem is the presence of two separate craters at the Gulf of Carpentaria site, said physicist Mark Boslough of Sandia National Laboratories in Albuquerque, New Mexico.
If a large impactor had broken up on its final approach to Earth, he said, the fragments would still have been very, very close together when they landed: "It essentially will behave as one piece," creating a single crater, Boslough said.
In addition, he said, Abbott and other members of an informal association called the Holocene Impact Working Group are finding evidence for more impact events than astronomers calculate should be possible.
Abbott and colleagues argue that several climate events during the Holocene epoch—11,500 years ago to the present—were actually triggered by impacts, and therefore such large impacts are more common than currently believed.
Boslough and other experts, meanwhile, have been cataloging asteroids and other bodies that cross Earth's orbit and calculating how frequently space rocks should strike the planet.
"We have a pretty good idea about how many there are and what the frequency of impact should be, and the abundances based on [the working group's claimed crater count] are orders of magnitude greater than what astronomers observe," Boslough said.
"It's pretty hard to imagine where these things could be coming from so that astronomers wouldn't see them."
Instead, it's more likely that the craters found by the working group have volcanic origins, the impact skeptics conclude.
Abbott acknowledges that her case for Carpentaria isn't 100-percent proven. But in general, she said, "I think we're getting very close to being able to show there were a lot of impacts in the last 10,000 years."
ping
So, it was either Krakatoa exploding or two massive asteroid strikes that caused the Dark Ages? Cool!!!!
Bush’s fault!!
I thought that was Barney Frank?
Meteorite iron was very much in demand during the Dark Ages. It was said that swords forged of iron from heaven were invincible in battle. Legend had it that Excalibur itself was forged from meteorite iron.
Shrug. Makes ya wonder.
Uh, 11 miles is not a tiny difference. It’s like the difference between a .22 on a necklace and the 30mm Vulcan cannon.
Also, that finding about diamonds, if they can be manipulated, could lead to some more resilient earth drillers.
“So, it was either Krakatoa exploding or two massive asteroid strikes that caused the Dark Ages? Cool!!!!”
Neither had anything to do with the culture/civilizational crash in Europe. You may be thinking about the little ice age.
EARLY MIDDLE AGES
No one definitive event marks the end of antiquity and the beginning of the Middle Ages. Neither the sack of Rome by the Goths under Alaric I in 410 nor the deposition in 476 of Romulus Augustulus, the last Roman emperor in the West, impressed their contemporaries as epoch-making catastrophes. Rather, by the end of the 5th century the culmination of several long-term trends—most notably a severe economic dislocation and the invasions and settlement of the various Germanic tribes within the borders of the Western Empire—had changed the face of Rome. For the next 300 years western Europe remained essentially a primitive culture, albeit one uniquely superimposed on the complex, elaborate culture of the Roman Empire, which was never entirely lost or forgotten.
“Paging Velikosky. Paging Immanuel Velikovsky. This is your medium calling...”
Were the Dark Ages Triggered by Volcano-Related Climate Changes in the 6th Century?
The only historical event that is more debated than "the Extinction of the Dinosaurs" is "the Fall of Rome". Sheesh!
According to those who keep track of these eruptions, the 5th century (416 AD) Karkatoa eruption VEI is unknown but certainly not very large - perhaps the equilivant of St Helens at best. These was no signifigant eruption again until 1883 AD.
see here:
http://www.volcano.si.edu/world/volcano.cfm?vnum=0602-00=&volpage=erupt&format=expanded#E1883520
The guy you reference may be right and si.edu may not have updated. But, he seems alone in his opinion. So I’m not going with ‘could have’, ‘perhaps’, ‘global climate modelers’, ‘tree ring data’, and ‘hypothetical’.
These are the documented eruptions during a 90 year period when the “Dark Ages” could have been effected by volcanism:
450 A.D. – Ilopango (El Salvador) Erupts
Volcanic Explosivity Index (VEI) = 6
540 A.D. – Rabaul, Papua (New Guinea) Erupts
300 million tons of aerosols.
Volcanic Explosivity Index (VEI) = 6
Each of these is 10X greater than St Helens.
But if it had broken up slightly earlier -- due to solar heating, say, or gravitational stresses -- that argument loses its force.
The climate change took place around 535 AD, while the asteroid impact happened in 500 AD. Don’t know if there is any documented climate change around 500 AD.
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Thanks Palter.To all -- please ping me to other topics which are appropriate for the GGG list. |
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