Slashdot Mirror
New NASA Maps Show A Bad Day On Earth
Stephen Lau writes "ScienceDaily has an article talking about the new NASA maps that reveal the geography of the North American continent in amazing detail. One of the maps provides strong evidence of a 112 mile wide, 3000 foot deep impact crater which they believe was the comet/asteroid impact that killed the dinosaurs and more than 70% of Earth's living species 65 million years ago."
Wasn't this in Slashdot about 2 days ago?
From the 7th - NASA Releases New Topographic Map of North America
Which means that a similarly-sized asteroid may be slightly less apocalyptic than thought. Sort of comforting, though I wonder how we'd deal with global forest fires when we can't even handle a relatively small number now.
If the site is slashdotted, you can just download the full-resolution image [617.7 megabyte TIFF]
HIV Crosses Species Barrier... into Muppets
Actually, it was "slashdotted" before it was posted here. I read it this morning and already then it was at a crawl. Could be because about 390 news articles already link to it?
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In this particular case, though, this research is verifying a long held belief that a giant asteroid/comet hit the Yucatan Peninsula. This is not news of a new asteroid.
Very popular slashdot journal for adul
Those images have been timing out since before the first comments appeared.
Original Caption Released with Image: This shaded relief image of Mexico's Yucatan Peninsula show a subtle, but unmistakable, indication of the Chicxulub impact crater. Most scientists now agree that this impact was the cause of the Cretatious-Tertiary Extinction, the event 65 million years ago that marked the sudden extinction of the dinosaurs as well as the majority of life then on Earth.
Most of the peninsula is visible here, along with the island of Cozumel off the east coast. The Yucatan is a plateau composed mostly of limestone and is an area of very low relief with elevations varying by less than a few hundred meters (about 500 feet.) In this computer-enhanced image the topography has been greatly exaggerated to highlight a semicircular trough, the darker green arcing line at the upper left corner of the peninsula. This trough is only about 3 to 5 meters (10 to 15 feet) deep and is about 5 km. wide (3 miles), so subtle that if you walked across it you probably would not notice it, and is a surface expression of the crater's outer boundary. Scientists believe the impact, which was centered just off the coast in the Caribbean, altered the subsurface rocks such that the overlying limestone sediments, which formed later and erode very easily, would preferentially erode on the vicinity of the crater rim. This formed the trough as well as numerous sinkholes (called cenotes) which are visible as small circular depressions.
Two visualization methods were combined to produce the image: shading and color coding of topographic height. The shade image was derived by computing topographic slope in the northwest-southeast direction, so that northwestern slopes appear bright and southeastern slopes appear dark. Color coding is directly related to topographic height, with green at the lower elevations, rising through yellow and tan, to white at the highest elevations.
Elevation data used in this image were acquired by the Shuttle Radar Topography Mission (SRTM) aboard the Space Shuttle Endeavour, launched on Feb. 11, 2000. SRTM used the same radar instrument that comprised the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) that flew twice on the Space Shuttle Endeavour in 1994. SRTM was designed to collect 3-D measurements of the Earth's surface. To collect the 3-D data, engineers added a 60-meter (approximately 200-foot) mast, installed additional C-band and X-band antennas, and improved tracking and navigation devices. The mission is a cooperative project between NASA, the National Imagery and Mapping Agency (NIMA) of the U.S. Department of Defense and the German and Italian space agencies. It is managed by NASA's Jet Propulsion Laboratory, Pasadena, Calif., for NASA's Earth Science Enterprise, Washington, D.C.
The flying hamster of DOOM rains coconuts on your pitiful city.
They had evidence of soil from the Yucatan peninsula in the K/T layer from outcroppings around to world, indicating that the impact took place there and scattered material specific to the peninsula, around the globe. Dinosaurs are found up to the K/T layer, but not above. This has been known for quite some time. The exact location of the crater was located around 1991 I believe, but was only corroborating evidence. The evidence comes from the composition of the K/T layer. This link might help.
0xfeedface
here is yet another government server for us to destroy. It has many similar pretty thing for you to look at.
http://photojournal.wr.usgs.gov
Cypherpunks: Civil Liberty Through Complex Mathematics. Those who live by the sword die by the arrow.
I managed to save some of the two catalog pages here:
:)
http://www.phule.net/mirrors/PIA03379.html
and
http://www.phule.net/mirrors/PIA03377.html
PIA03379.html has the 1.5MB image.
No, I'm not going to try and mirror the 600+MB TIFF file
In Soviet Russia...michael would be rotting in Siberia!
They can't be 100% absolutely positively certain, but they can get pretty close to certain. There are several ways to find out if a particular asteroid was the cause of a certain effect.
We can get fairly accurate dating of both the asteroid event and the extinction event. You can find out when the impact occurred by noting how deep the the impact site and the material ejected from it is buried and comparing it to the sedimentation rates in the area. You can also perform carbon dating or other isotopic analysis on material that was killed in the region of the event at the impact layer.
If the impact was large enough then the material that made up the asteroid should have been deposited around the world. Each asteroid has a "fingerprint" of different isotopes that is fairly unique, so the deposited layer can be identified as to which asteroid caused it. This means that there will be an identifiable layer of material in the arctic ice. Since each yearly layer has seasonal dark and light bands, just count the rings to find out how old the deposited layer is.
Dating the dinosaurs is also done pretty easily. Carbon dating and isotopic analysis can narrow down the date pretty well, as well as buried depth, sedimentation rates, and other geological identifiers. Finally, the layer that the dinosaur fossils are found in will have some of that isotopic "fingerprint" from the asteroid that impacted the Earth.
With this information you can narrow down both the impact date and the extinction dates to a narrow range. If those ranges overlap and the impact was large enough, you probably have the impact that caused the extinction. It turns out that there is probably the major impact in the Yucatan Peninsula and a few much more minor impacts that caused the extinction of the dinosaurs. We've known about this for years, but more evidence never hurts.
Sapere aude!
It's a very accessible read, and explains their thought processes quite clearly.
As I recall, the discovery of iridium, an element only found extraterrestrially (i.e. on asteroids), in the strata of rock that corresponds to the date of the extinction of the dinosaurs tipped them off.
-DZ
What about the rest?
:)
And yes I have a copy of the 30MB sized one already (I'm not crazy enought to download the CD sized one).
PIA03381:Shaded Relief with Height as Color and Landsat, Yucatan Peninsula, Mexico[30.85MB]
PIA03380:Anaglyph, Yucatan Peninsula, Mexico[5.193MB]
PIA03378:Anaglyph, North America[208.5MB]
PIA03377:Shaded Relief with Height as Color, North America[208.5MB]
PIA03379:Shaded Relief with Height as Color, Yucatan Peninsula, Mexico[617.7MB]
BTW wget is your friend.
Here is an annotated mirror which should help: Image
Carbon 14 is good for dating organic matter up to around 40000 years old... But there are other means of dating on a geological time scale. Forinstance, when certain minerals are melted and then cooled, they form with a crystalline structure aligned to the earth's magnetic field. By taking into account shifts in the alignment, the known rate of continental drift, comparisons to other nearby rock layers, etc, you can get a pretty good idea when those rocks initially cooled. Also, you can use radioactive elements with longer half lives than carbon-14 to date rocks, by comparing the ratio of that element to its decay products within the rock. This is what most often gets confused with radio-carbon dating, due to both techniques' reliance on radioactive isotopes. And don't forget just looking at the rock strata.... -- Horse_Pheathers
the vast majority of the impactor would have been either vaporized or shattered into tiny pieces (dust sized) by the deceleration and the conversion of kinetic energy to heat.
the yucatan (and other) impact craters that have been identified on earth are identified as impacts not just by their morphology! in fact the yucatan crater was not "seen" until after they inferred that it was there.
the other evidence includes geochemistry (such as the famous irridium "anomalies people like to bring up), tektites (tiny globs of glass caused by the impact), "shocked" quartz (in which the crystal structure has been severely modified by the stresses caused by the impact), coesite at the surface (coesite is a high-pressure polymorph of quartz usually only found in rocks deep in the crust), tsunami deposits (caused by the giant "tidal" wave resulting from an impact into shallow ocean), etc.
"A major reason for your GDP is because your country was founded on slave labour; helping it become the richest country in the world in no time at all."
When slavery was at it's peak, the US wasn't so 'rich'. That didn't happen until well after slavery was completely abolished.
The reason we don't usually get to see the original meteor is simply because it has been vapourised in the intense heat caused by impact ;) If you think about it, these things may be travelling at about 150 000km/h, and all that kinetic energy needs to go somewhere, so it gets transferred to heat energy - here's an experiment you can perform in your garage - strike a metal plate with a sledgehammer several times (wear ear protection!) not only might you see sparks fly, but feel the plate and hammer afterwards - it will be hot.
Meteorites usually contain high concentrations of Platinum Group Elements (PGE's) e.g. rhodium, palladium, and platinum. They also contain relatively high concentrations of irridium relative to earth because these bodies haven't had the chance to chemically differentiate them through the forces of gravity. Moreover, they have different isotope ratio's when compared with terrestial PGE's - this is how you know if it's terrestrial or not!
Now, when the impact event occurs, the atoms don't get destroyed, they get transferred to the target material. (you can vapourise the impactor, sure, but you can't destroy the atoms)
So you can look for these signatures geochemically, and in some cases you can even tell what type of meteorite hit the earth (stoney, iron or carbonaceous chondrite)
Reference: McDonald, I (2002): Clearwater East impact structure: A re-interpretation of the projectile type using new platinum-group element data from meteorites, Meteoritics and Planetary Science, vol.37 459-464
-- Fuck Beta
Actually, by your logic, where are all the meteors and other things that have hit the moon. There are bunches of craters there. And not one big meteor sitting in the middle. Actually, quite a bit of research into this crater has been done, there is a layer of a material (compacted dust, the actual material I cannot remember. Nickel and ferrite maybe.) all over the globe which roughly coincides with the estimated impact date. This "layer" seems to be thicker around the geographical regions near the impact site. Oh right, what about that crater in Arizona? Where's the rock that made that? My point is, albeit a bad one, there are some basic laws regarding transfer of energy (some physics major or 8th grader could tell you what they are) which basically dictate that the earth is this really big huge heavy rock. And you hit that rock with basically a little rock, something's gotta give. Typically the little rock. So either it gets liquified or what not. Where's the proof? Fire a lead pellet into a brick of lead at a very very high rate of speed. What do you get? A crater in the lead block, a fine coating around and in that crater of the lead that made up your pellet. How do we know it's not a sink hole? Because of the make up of the material's around an impact site that do not coincide with the native materials of the geological area?
feh
OK folks ... I think we may have a Band-Aid® "fix" for the dreaded Slashdot Effect on the NASA PhotoJournal.
/.'ed, there's about 9,000-12,000 HTTP packets going back and forth every second at the moment, according to tcpdump.)
What you have to understand is that the NASA PhotoJournal is not really intended for "casual users" as a rule. It's really more oriented towards researchers. Thus, you'll find, it was easy to download full-resolution TIFFs, and the stuff like JPEGs and GIFs was really somewhat of an afterthought. Meaning, basically, that methods (cgi-bin) were provided to create those JPEG images on the fly, from pull-down menus.
Basically, part of the "Slashdotting" of the machine was the CPU being eaten alive by all that cgi-bin on-the-fly conversion stuff.
What we've done (Band-Aid® fix) is to change the interface to be more "user friendly" until a final decision is made on how to orient the site - namely, what this means is that each page will now have a thumb, and clicking on the thumb will get you a modest-sized (pre-cached, not on-the-fly) JPEG image. The original full-sized TIFF image will be available from the menu on the lower-right of the page. In addition, full-scale JPEGs are currently being generated on a back-end machine, so when those are done, they'll be transferred over and then a link/menu entry for getting the full-sized JPEGs will be provided as well as the TIFF link.
While the load average is still high, I think responsiveness should be doing better now.
(Just for fun, in case you've never been
For the record:
Iridium is found on the Earth, but only in small quantities. The iridium anomaly is a band of clay greatly enriched in iridium over background levels.
Earthly processes can concentrate iridium, even on fairly large scales, but not even approaching the degree needed to explain the very high levels observed, let alone the world wide extent of the enrichment.
It's also worth pointing out that not all non-earthly bodies are enriched in iridium, so it's possible to suffer an impact event without iridium enrichment.
On the subject of mass extinctions and impacts: most of the notable mass extinctions in the Earth's history have apparently not been caused by impacts. Really large extinctions are fairly rare (depending on how you count, there are about five really big ones), and comet/asteroid impacts are much, much, more common.
It's possible that this paricular impact was especially disasterous because it hit close to North America where most of the dinosaurs lived, it was a very large impact, it hit in the ocean which generated exceptionally large tsunamis as well as water vapor, it hit limestone which was vaporized to produce CO2, and there was gypsum or anhydrite interbedded with the limestone which would have produced unpleasant sulfur compounds including sulfuric acid rain...but that's hardly the whole story. Still, it is a rather unpleasant start.
- Anonymous Coward