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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.
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.
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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
Since this is a dupe from last week, I had already downloaded the TIFF of the North America image, and converted it to a 1600x1200 JPEG.
You can grab it here.
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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
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 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