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In 2001, the Earth-observing satellite Landsat 7 took the above image of Egypt. Now, the dashed circle (and the blog entry title) make it pretty obvious what’s going on here, but for a moment look at the picture’s features and pretend the circle isn’t there. Now swear to tell the truth: you’d never ever see a crater in there, would you? I know I wouldn’t have.
And that’s how a crater 31 kilometers across stayed hidden: in plain sight. It’s so freaking huge no one ever noticed it before. Farouk El-Baz spotted it, but then, he has experience. He trained the Apollo astronauts in lunar surface geology (and if his name is familiar, a shuttle in Star Trek: The Next Generation was named after him).
El-Baz knew that there was a greenish glass found in Egypt called "impact glass". It’s commonly formed when a big meteorite slams into the ground; the tremendous heat and pressure fuse the sand underneath it into glass (a big impact can dwarf a nuclear bomb in energy produced, although the temperature is much lower). So El-Baz used satellite imagery to poke around, and voila.
He has a great eye for this, obviously. Remember, he didn’t have a dashed circle to guide his view.
The raised rim is pretty clear once you see it. The impactor must have been huge, probably over a kilometer across. Anything within a thousand miles of the impact had a pretty bad day — I estimate the yield at roughly 200,000 megatons, though I might be off by a factor of two or three. For comparison the largest nuclear weapon ever detonated was about 60 megatons. The fireball would have been as hot as the surface of the Sun, and just the heat of impact would have wrought damage on an incomprehensible scale. Then the blast wave started expanding outward in a circle, and the real destruction would have begun…
The crater was immense, but a hundred million years of erosion has worn it down to a chain of hills difficult for the eye to see. Still, it sat there all that time, just waiting to get noticed. We never saw it, and it’s right here on Earth! What awaits us on other planets?’
March 14th, 2006 at 10:24 am
Any information as to the age, other then a hundred million years? I’m wonering if it’s tied to any minor die-off in the fossil record (or, for that matter, any major die-off). I know there’s no significant periodicity found in extinction events, but impacts of this scale always make me wonder what happened to the locals.
March 14th, 2006 at 10:53 am
That is absolutely fascinating, Phil. I wonder how many other such craters here on Earth have escaped detection.
March 14th, 2006 at 11:00 am
Phil
Can you give a more detailed location? I’m in Egypt, and I have the NASA coverage for the whole country – I’d be interested to try and have a closer look.
March 14th, 2006 at 11:45 am
Nick, try here: 24º 40′ N, 24º 58′ E. It straddles the Libyan border.
March 14th, 2006 at 11:46 am
How many other craters? How long is a piece of string?
But see how many HAVE been found at the Earth Impcat Database:
http://www.unb.ca/passc/ImpactDatabase/
John
March 14th, 2006 at 12:06 pm
Fascinating, Phil; I especially find myself dwelling on the issue raised in your last paragraph. Even just eyeballing the math… assume that there is an impact of comparable magnitude every ~100,000 years, and also consider the Earth’s approximate age at ~4,000,000,000 years. There would be ~40,000 such impacts in our history. So now, assume a crater like that can be almost unrecognizably worn down in ~100,000,000 years, so that craters younger than 100,000,000 years old are at least remotely able to be discovered. Considering that ~71% of the earth’s surface is covered with oceans, we should expect to find somewhere in the area of 300 of these buggers that made landfall.
How many of these do we know about? Certainly nowhere near 300!
Great post!
March 14th, 2006 at 1:22 pm
While I don’t usually like to dispute experts in their field, I remain unconvinced this is a crater. I have looked at the picture, and followed the link to the close-up view. I don’t see any objective reason to pick the erosional features that he does to form that oval, other than the slight curve of the top features. The rest of the marks seem indistinguishable from the rest of the erosional features all over that image.
Now, I appreciate the existence of the “Desert Glass” is evidence that there was an impact somewhere in the area. I just don’t see enough justification that this is a crater, even weathered.
March 14th, 2006 at 2:08 pm
You are right to say that it’s not a crater. It’s only the barest remnant of an ancient crater. The shock-quartz, or “impact glass” is the primary evidence that it once was a crater.
There may be other significant evidence as well, but here I’m just speculating. For instance, the Chixiclub crater in the Yucatan can be detected by the anomalous gravity signature resulting from the crater being filled with different materials than the surrounding rock. Perhaps that same mechanism could show up here as well.
Also, craters leave tell-tale evidence in how they distort the previously-planar layers of rock they impact. In the central area the rock is either vaporized or ejected, but along the raised rim the layers are tilted towards the center of the crater. Additionally, the layers outside the rim can be inverted when they are tossed out of the crater. These types of stratigraphic evidence can also indicate a fossil crater.
So, you are right to be skeptical, but the shock quartz evidence is very strong. And further evidence, though not discussed by Phil, may have been collected to shore up the argument that a crater used to exist there.
March 14th, 2006 at 2:32 pm
Indeed, lots of old craters are hard to recognise just by eye. I live about hundred miles or so from the Kentland crater, in Indiana. Possibly no one would even have guessed were it not for the anomalous presence of the central uplift, the peak that was produced by the liquefacted soil rushing in to fill the vacuum generated by impactor. The rim is all eroded away at the surface and has only been mapped out with gravimetric surveys.
The peak is rich in lots of useful rocks which are otherwise at too great a depth to be mined economically. The uplift propelled the stuff up to where it can be dug right out. In fact, it’s now a commercial quarry.
March 14th, 2006 at 2:35 pm
Wonder if Dr. Shoemaker ever saw it?
March 14th, 2006 at 2:44 pm
This makes me wonder aswel…. how many have we missed ebcause they are to large, under water, or almost erroded gone.
March 14th, 2006 at 2:46 pm
BA, I recognised Farouk El-Baz’s name from Andrew Chaikin’s book (A Man on the Moon). I’ve watched just about every episode of Star Trek: TNG, but do not remember the names of any of the shuttles.
March 14th, 2006 at 3:22 pm
This has spurred others to look for more craters:
http://www.astroseti.org/impacts.php
And more have been found.
March 14th, 2006 at 3:30 pm
Remember that erosion is a very powerful force. The physical characteristics of an impact crater don’t last in a pristine state for long in geologic time. If that crater is 100 myo it has been around 16x longer than the Grand Canyon. The effects and byproducts, shocked quartz and grav. anomalies of the impact outlast the physical footprint.
March 14th, 2006 at 3:50 pm
It’s just a little south east from the BP Structure crater, but a hell of a lot bigger. If you locate BP Structure on Google Earth, from an eye-alt of 200km, it’s in the same field.
March 14th, 2006 at 4:10 pm
There seems to be another crater at 24º 35′N, 24º 24′ E, clearly visible in GE with an altitude setting in the region of 20 miles.
Its size is mid-way between the Kebira crater and the BP Structure.
March 14th, 2006 at 4:27 pm
Regarding the 60 megaton bomb (the most powerful ever to be constructed), it was featured in a recent story at Damn Interesting. Here’s a teaser:
“Despite the cloudy weather, the flash of light was visible as far as 1,000 kilometers distant, though the sound of the blast would not reach that far for forty-nine minutes, in the form of an indistinct, heavy blow. The giant fireball reached from ground-level to about 34,000 feet into the air, violently releasing 3800 times more explosive energy than the Hiroshima bomb– equivalent to fifty million metric tons of TNT. One hundred kilometers from ground zero the heat would have inflicted third degree burns. Atmospheric focusing produced areas of destruction hundreds of kilometers from ground zero, including wooden structures which were completely destroyed, and some shattered windows in Finland. The explosion’s atmospheric shockwave traveled around the Earth three times before it dissipated.”
“The mushroom cloud which followed the blast was enormous in scale. It stretched sixty kilometers into the sky, and had a diameter of about forty kilometers. Ionization from the explosion disrupted radio communications for the better part of an hour.”
There’s also a link to a Google Video clip of the bomb drop, in the comments. Now, 60 megatonnes is certainly bad enough, by the above description – can’t even begin to imagine a 200,000 megaton blast… let alone the much larger one that wiped out the overgrown lizards. Whew! :O
March 14th, 2006 at 6:17 pm
As luck would have it, there are also formations that look like ancient craters but probably aren’t. The East side of Hudson Bay, Quebec has always looked like part of an enormous impact crater to me.
March 14th, 2006 at 6:46 pm
Nigel,
The very first shuttle, really just a test one…never flew in space is the
ENTERPRISE!:) Named for, you guessed it…Star Treks’ Enterprise.
March 14th, 2006 at 6:59 pm
Makes me think that the Great Pyramids were built for use as a bomb shelter. How large was the explosion that caused the Arizona Metor Crater? So much data—so little time for conclusions on how many craters once peppered the Earths surface. Those massive oceans are the real erosion machine that just washes out all the evidence from the past. Very intresting post 4-sure….
March 14th, 2006 at 7:12 pm
Phil & everyone,
Check out Red State Rabble..this is too funny.
Creationist Ken Hovind Director of the “Creationist Dino Park” in Florida
is in BIG trouble….seems that he never got the ok’s for Zoning…among some other real problems!
March 15th, 2006 at 2:34 am
The 200,000 megaton bit: Does that refer to the mass of the impacting rock, or is it the TNT equivalent?
March 15th, 2006 at 3:42 am
Hello Edward,
I think NIgel is refering to the names on the shuttlecraft carried onboard the starship Enterprise. For example, on TOS there was one named “Galileo”. On Next Generation there were several named shuttlecraft, for example one was named “Feynman”.
March 15th, 2006 at 6:25 am
Bomb/explosive yields are expressed as amounts of TNT, yes.
March 15th, 2006 at 6:39 am
TO JOHN D:
Thanks for the information about the Earth Impact Database. Learn something new every day.
March 15th, 2006 at 9:31 am
To P E M,
Did you hear about the VVIP row at the very front of the Enterprise rollout vewing stands ?
Richard
March 15th, 2006 at 10:06 am
Does anyone want to tell the current Adminstration that the Solar System possesses WEAPONS OF REALLY REALLY MASS DESTRUCTION! And that that they could be launched at American soil with nary a warning?
It’s all a matter of packaging: if we want to revive NASA’s plan for exploring the local universe we have to convince Karl and Dick and whazz his name that we need to INVADE THE SOLAR SYSTEM IMMEDIATELY. We can call it Operation Mars Or Us and we’d be on Mon Olympus within two years!
March 15th, 2006 at 10:13 am
The Enterprise situation is a fiasco. People were so adamant to get the “First” shuttle named Enterprise that they actually got the drop test simulator named Enterprise.
True, the plan at the time was to convert the drop test simulator into a full Shuttle, but that didn’t happen.
March 15th, 2006 at 10:25 am
As far as I know there was no mass extinction at 100 million years ago (in fact it looks like there is a spike in the number of species around that time), there was one 200 million years ago and another 65 (which has already been discussed), as well as a minor one around 150 million years before. There isn’t even any major transition at that point (the Jurassic/Cretaceous transition dates back to about 150 million years). Now what would be interesting is if the date is a bit off, and it is really 150, 200, or especially 250 million years old. That would be really big news. A 65 million year old crater would also be significant, indicating a multiple impact event.
March 15th, 2006 at 10:29 am
Anthony Kendall Said:
>You are right to say that it’s not a crater. It’s only the barest remnant of an ancient crater. The shock-quartz, or “impact glass†is the primary evidence that it once was a crater.
I’m uncertain from the article on the geographic distribution of the shock-quartz. Localized to this region would make sense. Scattered across this and other regions would be less convincing. I’m not saying impacts haven’t happened in the region, I’m just doubting that this is the specific remains of a crater.
>So, you are right to be skeptical, but the shock quartz evidence is very strong. And further evidence, though not discussed by Phil, may have been collected to shore up the argument that a crater used to exist there.
Certainly any other evidence collected would be valuable. But the linked article doesn’t discuss other evidence. It discusses the shock-quartz from the standpoint of original data that caused El-Baz to start looking for the crater. He was asked if the crater could be identified and he replied no, but then decided to see if he could. This is his conclusion. That doesn’t mention other evidence.
This crater appears to be determined purely visually by El-Baz. It appears to me to be picking the items that fit the pre-conceived notion there is a round crater here. I don’t see anything other than the one curve on the top clump of erosion to suggest there’s a round spot here. The rest of the points on the dotted line appear to me to be picked because they are handy. I see no objective reason to pick them and not the similar features that surround them. That is my point. Any contextual evidence or ground evidence to support that choice would be great. Heck, a statement that the crater wall definition is a guess would be nice. It seems to me too defined without justification for that definition. That’s my reservation.
Maybe what I’m asking is to understand the details of El-Baz’s professional judgement. What is it he sees that defines this as a crater with the walls where he puts them?
March 15th, 2006 at 1:46 pm
Does it look like a smily face to anyone else?
200 Megatons is a pretty good fireworks show. I wonder what the fossil record in the area is like.
It would be interesting to see how long animal life took to return to the immideate area around the crater.
Contrasting local and global instictions (like that caused by Chicxulub impact) could be insightful.
It would give us a good idea of just how much damage could be done- and how long it would take to repair- next time a rock hits us.
March 15th, 2006 at 2:42 pm
Where is the proof that this structure is an impact crater? According to the BU Press
Release there are only satellite images yet no field studies so far. Gene Shoemaker
himself taught me (i.e. told me during a lunch break at Fred Whipple’s 90th birthday
party, to be exact) that you must not trust any impact crater until you’ve been digging
around in it yourself – there are just too many other round structures in terrestrial
geology. So publishing this discovery as an impact crater, let alone the source of the
desert glass, instead of calling it a “crater candidate”, was Bad Astronomy indeed!
March 15th, 2006 at 3:09 pm
Where is the picture?
March 15th, 2006 at 4:54 pm
To add to the Kebira structure discussion, the Paper:
“Discovery of the largest impact crater field on Earth in the Gilf Kebir region, Egypt”, Philippe Paillou (et al), documents the presence of shattercones and planar deformation features in the structures documented in the paper. These are positive indicators of an impact event. This crater field is
March 15th, 2006 at 5:03 pm
To add to the Kebira structure discussion, the Paper:
“Discovery of the largest impact crater field on Earth in the Gilf Kebir region, Egyptâ€, Philippe Paillou (et al), documents the presence of shattercones and planar deformation features in the structures documented in the paper. These are positive indicators of an impact event. This crater field is less than 300 km to the east of the Kebira structure. A field trip to the Kebira structure will be required to finally determine if it is an impact crater (or not).
To add further to this “crater search” discussion, for some time now I have thought that “maybe” the Manicouagan structure is a “double” impact site comparable to the Clear Water Lake double craters, both in northern Quebec, Canada.
Looking at the Manicouagan structure at N 51° 23′ W 68° 42′, notice that
there is a “second” circular structure immediately to the north. I have
illustrated this at: http://www.ottawa.rasc.ca/astronomy/earth_craters/possible_craters/index.html (look half way down the page) I highlighted the “circular” structure on the aeronautical chart. The geology in the area shown on the aeronautical chart reveals that:
a.. The contour lines denoting an increase in elevation of the Precambrianrocks to the north of the structure follows a semicircle;
b.. Two rivers on the east and west of the feature form an enclosingsemi-circle around the structure; and
c.. There is a central peak.
This could simply be the result of my “fertile” immagination, or could it?
Charles O’Dale
Meeting Chair
Ottawa RASC http://www.ottawa.rasc.ca/astronomy/earth_craters/index.html
March 15th, 2006 at 7:38 pm
Those arced hills at 2 and four o’clock, as will as the long one between 10 and noon would be a good indication of a crater. I an wondering if he had access to a topographic map of the area.
I hae read somewhere that when Galileo first saw large craters on the Moon, he described it as being a walled plain, like Bohemia. Has anyone checked that area to see if there are any signs of an impact?
March 25th, 2006 at 10:45 am
Can I ask how you figure on 200,000 megatons equivalent for the impact strength. I would be interested in the inputs of the equation.
If one hit Earth today, likely it would land in the Ocean. Are we able to detect crater marks on the surface of the Ocean? Whats the biggest crater impact we know of in the solar-system?
July 10th, 2006 at 11:10 am
“Kebira”, just like Paillou’s “crater field”, appears to be the product of trying very hard to find exactly what one is looking for.
We recently visited the “Kebira” area, and found the “central uplift” to be an eroded outlier of the surrounding sandstone plateau, with undisturbed horizontal bedding throughout. The feature is the result of erosion, no evidence of impact origin.
The same is true for Paillou’s crater field, which have been visited both by myself and several other geologist groups. All the features described are clearly non-impact origin.