Sankar Chatterjee (Texas Tech) and a team of researchers have been looking at something known as the Shiva basin, that area west of India that is heavily laden with oil and gas resources. Chatterjee believes the Shiva basin is in fact a huge, multi-ringed impact crater, one caused by a bolide perhaps as much as 40 kilometers in diameter, big enough, as the scientist says, to create its own tectonics. The supposed dinosaur killer impactor in the Yucatan, by contrast, is thought to have been between eight and ten kilometers wide. Is Shiva basin the crater left by the actual extinction event?
Mostly submerged, Shiva’s outer rim forms a 500-kilometer ring with a central peak extending some three miles from the ocean floor. One result of such a strike, if the team’s theories hold up, is that the volcanic eruptions at the nearby Deccan Traps may well have been enhanced, not to mention the ensuing formation of the Seychelles Islands, which would have broken off the Indian tectonic plate. We’ll learn more about this theory when the team goes to India to look at rocks from the center of the presumed crater. Says Chatterjee:
“Rocks from the bottom of the crater will tell us the telltale sign of the impact event from shattered and melted target rocks. And we want to see if there are breccias, shocked quartz, and an iridium anomaly.”
Image: This diagram shows a three-dimensional reconstruction of the submerged Shiva crater (~500 km diameter) at the Mumbai Offshore Basin, western shelf of India from different cross-sectional and geophysical data. The overlying 4.3-mile-thick Cenozoic strata and water column were removed to show the morphology of the crater. Credit: Sankar Chatterjee, Texas Tech University.
On a similar note, I see that a new title focusing on the Tunguska event is coming to our shelves, and let’s hope it attracts the interest of people still unaware of the power of such impacts. The Tunguska Mystery (Springer, 2009) works through the various investigations into the nature of the impactor, and from the press release I’ve seen notes the urgency of solving the asteroid vs. comet question, given our need to protect against future strikes. The author, Vladimir Rubtsov, has been a prolific writer of popular science articles published in Russia and internationally.
I hasten to add that I haven’t seen this one yet, but I’ll update this note when I’ve had the chance to page through the book. From the Amazon site I learn that Dr. Rubtsov “…joined the laboratory of Dr. A. V. Zolotov in Kalinin (now Tver), where for three years [he] studied the problem of the Tunguska explosion.” That was back in the 1970s, and was followed by a doctoral thesis with an interesting title: “Philosophical and Methodological Aspects of the Problem of Extraterrestrial Civilizations.” We’ll see how the scientist pulls together current thinking on Tunguska, the nature of whose impactor strikes me as less of a mystery than a fairly well constrained scientific question still in the process of being solved.
Comments on this entry are closed.
I’m a bit swamped right now, but I’m waiting to see what Chatterjee has offered for evidence that it IS an impact. The last consensus I heard was that it was not accepted as such, despite being pushed for now about 7+ years.
Just the other day I read an article titled “Comet alert” in the Oct. issue of “Spaceflight” in which a theory is presented whereby the Tunguska event was the result a ‘glancing blow’ by the NEO 2005NB56 — which is due back in our neighborhood in 2045. The theory, by Russian scientists E.M. Drobyshevski, T.Yu. Galushina, and M.E. Drobyshevski, was evidently also given popular coverage by “Popular Mechanics” a few months ago ().
I strongly recommend that readers here peruse the 1st poster, Will Baird’s blog…
Excellent paleontology, space science and rocketry commentary.
I just hope Vladimir Rubtsov isn’t one of those folks who try to explain the Tunguska event as the crash and explosion of a nuclear-powered alien starship.
I am not saying it couldn’t ever happen, but I blame that particular story on a “perfect storm” combination of the Cold War themes of UFOs, nuclear bombs, and people not appreciating just how much kinetic energy even a relatively small space rock can release when it hits our planet at tens of thousands of kilometers per hour.
When I first heard of Tunguska in the early 1970s, the trendy theory being touted was that a mini black hole had hit the Siberian tundra and plowed right through Earth back into space. Black holes were just coming into vogue with the discovery of Cygnus X-1.
Asteroid explosion over Indonesia raises fears about Earth’s defences
An asteroid that exploded in the Earth’s atmosphere with the energy of three Hiroshima bombs this month has reignited fears about our planet’s defences against space impacts.
By Tom Chivers
Published: 10:23AM GMT 27 Oct 2009
On 8 October, the rock crashed into the atmosphere above South Sulawesi, Indonesia. The blast was heard by monitoring stations 10,000 miles away, according to a report by scientists at the University of Western Ontario.
Scientists are concerned that it was not spotted by any telescopes, and that had it been larger it could have caused a disaster.
The asteroid, estimated to have been around 10 metres (30ft) across, hit the atmosphere at an estimated 45,000mph. The sudden deceleration caused it to heat up rapidly and explode with the force of 50,000 tons of TNT.
Luckily, due to the height of the explosion – estimated at between 15 and 20 km (nine to 12 miles) above sea level – no damage was caused on the ground.
However, if the object had been slightly larger – 20 to 30 metres (60 to 90ft) across – it could easily have caused extensive damage and loss of life, say researchers.
Full article here:
Wednesday, April 07, 2010
Could a Comet Tail Have Scarred the Earth in the Recent Past?
The idea that the Earth shows signs of having repeatedly passed through the tail of a comet does not bear up to scrutiny.
One of the puzzles that geologists occasionally ponder is the nature of eskers and drumlins.
Eskers are winding ridges a few tens of metres high that look remarkably like railway embankments. Indeed they are often used as readymade roads and run up and down hills over distances that sometimes stretch to hundreds kilometres.
Drumlins, on the other hand, are tear drop-shaped hills a few tens of metres high and a hundreds of metres long. They often appear in large numbers with the same orientation in drumlin fields .
Geologists have long assumed that eskers and drumlins are formed by glaciers and left behind after these ice giants retreated.
There are essentially two problems. The first is the internal structure of these formations. Eskers and drumlins have have an outer layer of water-borne clay and silt with attendant fossil debris. This covers an inner core made of unsorted boulders and rocks which are entirely free of fossils. These inner cores do not appear to have been affected by the action of water. How does this structure arise?
The second is that if glaciers are responsible for eskers and drumlins, they ought to be forming now. And yet nobody can find anywhere on Earth where these structures are currently forming.
Today, Milton Zysman and Frank Wallace publish on the arXiv their explanation for the formation of these objects and it makes for fascinating, if not entirely convincing, reading.
Zysman and Wallace say that eskers and drumlins are the debris left on Earth after our planet repeatedly passed through the tail of a giant comet. They say this explains the distribution of eskers and drumlins, which often form in roughly parallel lines.
It also explains their internal structure. The rocky core of these objects is pure cometry debris which explains the absence of fossils. The outer layer built up later through the action of water and ice.
The cometary origin, they say, also explains the rather unique shape of the individual rocks in the cores and the striations that mark them predominantly in line with their longest axis. (Apparently, these markings are consistent with the process of erosion that must occur in comet tails.)
Zysman and Wallace also point out that the ice age that is associated with esker and drumlin formation must have been caused by the comet tail, which would have enveloped Earth in a layer of dust that rapidly cooled the planet.
This is not an entirely new idea. Various commentators have suggested that many of Earth’s rocks and much of its water and atmosphere may have come from comets. And indeed this paper is an edited version of one the authors originally gave in 1997.
However, Zysman and Wallace’s idea as it stands is little more than an interesting guess. What of isotopic evidence? Presumably the isotopic content of the rocky cores should differ in a measurable way from material on Earth that has other origins. If this work has been done, they make no mention of it.
And the fact that we have not seen eskers and drumlins forming in the two hundred years that we’ve been looking does not mean they did not form in the past, during the many millennia that glaciers were ravaging the Earth. (In fact, there are recent reports that scientists have seen a drumlin forming for the first time in Antarctica.)
And finally, it’s hard to imagine that the debris from a comet tail hitting the atmosphere at several tens of kilometres per second would then land in a tear drop shape just a few tens of metres in size or form a line a few tens of metres wide but hundreds of kilometres long.
It should be straightforward to refute or dismiss this idea by simulating of the kind of debris patterns that this kind of event would produce. And in any case, the heat generated when rocks enter the Earth’s atmosphere melts their outer surface, giving them a “fusion crust” that is easy to identify. Why don’t the rocks in esker and drumlin cores have fusion crusts?
Putting Zysman and Wallace aside, however, it is still possible that the Earth has been shaped by extraterrestrial forces in ways that we are only beginning to grasp. For example, there is growing evidence that the Solar System has been regularly disturbed by passing stars and their accompanying discs of ice and dust. These events must have had a dramatic impact on our world.
It is becoming increasingly clear that conditions on Earth are a product of the interplanetary and interstellar environment in ways we are only beginning to understand. And of course we need new hypotheses to explore this idea to its fullest extent.
Ref: http://arxiv.org/abs/1004.0416: Tails of a Recent Comet: The Role Cometary Jets Play in Crustal Formation Esker/ Drumlin Swarms