Last week's meteor in Russia is being compared to the Tunguska event that took place in Siberia over a century ago. We posted about it previously, so if you're wondering what that was exactly, you can learn all about it here:
Phil Plait, astronomer, lecturer, and blogger at Bad Astonomy gives a humorous and informative talk about asteroid impacts both in the past and in the future. He touches on the asteroid that wiped out the dinosaurs 65 million years ago, and the 50 meter-wide asteroid that created Meteor Crater in the Arizona desert 50,000 years ago, and the rocky bolide that exploded with the force of 1000 atomic bombs above the Tunguska river region in Siberia in 1908. Each impacted with Earth, and lucky for us, they all took place safely in the past. But you know it’s bound to happen again. It’s not a question of if, but one of when. And when could be sooner than you think. Plait ratchets up his talk’s anxiety level with the information that an asteroid discovered in 2004 and known as Apophis is headed toward Earth. This thing isn’t anywhere as huge as the 6-mile wide space rock that ended the reign of the dinosaurs, but at over 250 meters across it could still do some serious damage.
In 2029, Apophis will pass so close to Earth it will come inside the orbit of some of our weather satellites. It won’t strike our planet at that time but if it manages to pass through a small kidney-shaped region in known as a gravitational keyhole, Earth’s pull would redirect Apophis orbit into one that would set it on a path of collision with us the next time it comes around on April 13, 2036. Sure the odds are slim everything will actually line up right for this to happen, but Plait sees it as an opportunity for us to learn how to deal with such events. We know impacts happened in the past, and we can assume they'll continue to happen in the future. Apophis is a good example of that. So it makes sense to start planning on how we can defend against such an event. Scientists from organization such as the B612 Foundation and NASA are already trying to raise public awareness of the dangers asteroids and other near Earth objects may pose to the future of our planet. And Plait explains some interesting counter offensives already being considered. It won't be an easy task but it's probably one that needs planning just in case. Besides, look at what could happen if we don't. It's a no-brainer.
A team of scientists may have finally found a possible impact crater from the Tunguska event that blasted above Siberia nearly a century ago.
On June 30, 1908, some sort of extraterrestrial object, such as a comet or an asteroid (at least according to the consensus), exploded in Earth’s atmosphere above the Tunguska River with such force that it flattened more than 2000 square miles of forest. But until now, no viable impact site had ever been found.
This whole Tunguska thing is cloaked in so much mystery and mythology, that agents Muldar and Scully could do a whole X-Files episode about it (in fact, they did). Well, the truth may be out there, but there’s a whole lot of it that remains unknown.
What’s is known is that something big exploded over the Tunguska river region in 1908. The place, unfortunately, is so out-in-the-middle-of-nowhere; it wasn’t scientifically investigated until more than two decades later when mineralogist Leonid Kulik led the first official expedition into the region in 1927. Kulik had initially come upon the site six years earlier when he doing a survey for the Soviet Academy of Sciences. Local eyewitness accounts convinced him that the explosion had been caused by an enormous meteorite impact, and he persuaded the Soviet government to fund the expedition in hopes of salvaging meteoric iron for Soviet industry. But to his disappointment, no possible impact crater was ever located (except in one bare location that later proved to be just a bog). What the expedition did find was a huge area of forest flattened out in a butterfly pattern. Oddly, the only trees still standing were located at ground zero, but those had been stripped bare of all their leaves and bark.
Kulik didn’t find any chunks of iron either, although later expeditions did find microscopic traces of nickel and iron in the soil.
But now, a University of Bologna team of scientists claims that Lake Cheko, which is located just 5 miles north-northwest of the explosion’s epicenter, shows some interesting features that could be interpreted as resulting from some sort of impact, perhaps from a small chunk of the disintegrating space rock – if that’s what it was. The team’s research appears in the online journal Terra Nova.
But other scientists aren’t jumping on the bandwagon just yet. For one thing the lake exhibits almost none of the usual telltale physical markings of an impact crater, other than being uniquely funnel-shaped unlike other neighboring lakes. And even then, its shape is more elliptical than circular. Cheko’s rim is not raised and lacks any sign of upturned ejecta. The scientists have found no shocked terrestrial rock in or around the lake, and to date no meteoric material either. And even if some is found, skeptics say it could have washed into the lake from the surrounding landscape. Also, trees older than a hundred years old are still standing near the lake. If Cheko were an impact crater, the force of the collision would have knocked them all down. It’s true that the lake doesn’t appear on any map prior to 1929, but the region is extremely remote, and there is some folklore evidence of its existence before then.
Other scientists speculate that the source of the event wasn’t from outer space at all, but rather was caused by geophysical forces, such as a cataclysmic gas blow out from deep inside the Earth. It just so happens that the Tunguska event epicenter sets at the intersection of a number of tectonic faults, and atop the ancient crater of a paleovolcano. Kimberlite pipes are also found in the area, an indication of magma reservoirs deep beneath the surface. And evidently there was a lot of earthquake activity in the Tunguska epicenter region back in 1908.
Andrei Ol'khovatov, a former Soviet scientist who is now -in his own words- “an independent researcher/expert” on everything Tunguska, has an entire website addressing this and other possibilities about the event. He has participated in a number of International Tunguska conferences, and I found his site very interesting to peruse.
So, whatever the Tunguska event was, whether it was a comet or asteroid, a UFO, an errant radio transmission, or the real cause of global warning - it exploded about 3-6 miles above the ground, knocked down a whole lot of lumber, scared the dickens out of the locals, and illuminated the sky so brightly it could be seen in London, a third of the way around the globe!
The Italian team plans to return to Lake Cheko in 2008 to perform further tests, including drilling into the core of the lake to examine an anomaly detected some 10 meters below the lake bottom. It could be a meteorite fragment or maybe just some compacted mud. I guess we’ll have to wait and see.
A new theory suggests that a blast from space 13,000 years ago may have been responsible for changes in Ice Age human cultures, and for wiping out most of North America’s large mammals, a fate similar to what large dinosaurs may have met 65 million years earlier.
The extraterrestrial blast from a large object, such as a comet or asteroid, colliding with Earth would have caused a significant climate cooling over the North American continent lasting for centuries.
According to Dr. Richard Firestone of Lawrence Berkeley National Laboratory, in California, the source of the collision may have originated from a supernova explosion that occurred about 250 light years from Earth.
“Our research indicates that a 10-kilometer-wide comet, which may have been composed from the remnants of a supernova explosion, could have hit North America 13,000 years ago,” says Firestone. “This event was preceded by an intense blast of iron-rich grains that impacted the planet roughly 34,000 years ago.”
Firestone and co-researcher Alan West say evidence of the supernova’s initial shockwave can be found in tiny impact craters in 34,000 year-old mammoths tusks. The two men theorize the tiny craters are the results of iron-rich grains traveling at 10,000 kilometers per hour slamming into the enamel.
Other evidence supports the comet impact theory. Sediment layers at some 22 prehistoric sites across the continent, show high of levels of iridium, along with concentrations of tiny diamond chips called nanodiamonds. There’s also a black layer of high carbon content that researchers argue could be the remains from wildfires ignited by the blast that swept across the continent.
No crater is known but scientists suggest that ice sheets present at the time may have been thick enough to act as a buffer against the collision.
It’s also possible the space rock exploded in the atmosphere but even then a shockwave of intense heat that would have wiped out everything in its path for miles around, and would have caused immediate and long-term damage to any existing human cultures. Glacial ice would have melted and surged into the North Atlantic, changing currents and effects on climate for centuries.
Such an event seems to coincide with the onset of what’s known as the Younger Dryas Episode, a period of significant environmental changes, Paleolithic cultural development, and mega-fauna extinctions.
All the large mammals that once populated the North and South Americas disappeared suddenly right about the estimated time of the extra-terrestrial impact.
"All the elephants, including the mastodon and the mammoth, all the ground sloths, including the giant ground sloth - which, when standing on its hind legs, would have been as big as a mammoth," said Professor James Kennett, from the University of California in Santa Barbara.
"All the horses went out, all the North American camels went out. There were large carnivores like the sabre-toothed cat and an enormous bear called the short-faced bear."
The effects of such a sudden extinction would certainly impact human populations as well. And that seems to be what happened. A number of prehistoric cultures such as the Clovis seem to have disappeared around the same time.
The new theory will be presented and hashed out this week at the American Geophysical Union's Joint Meeting in Acapulco, Mexico.
LINKS AND MORE INFO