Impact Ejecta - An overturned flap of latest ejecta on the terrace terrane. Anderson Study of the Manson Impact Structure MIS Drill cores, cutting samples from water wells, and seismic data has led to a good understanding of the geometry of the well-preserved impact structure. Fun Facts Only Naturally soft water in Iowa - within a few miles outside of Manson, the water changes from soft to hard. High Fluroride content in water turns teeth brown - was once a problem but a water purification system was put in place and it is no longer an issue.
Extremely high salt content in water - was not an issue for townspeople in comparison to the fluoride although increased salt intake is known for high blood pressure and heart disease.
The high salt content was removed in the purification system as well. In everyone knew Manson was special - the townspeople found out through drilling a well. The wells in Manson have to be drilled to feet while the norm for wells is - feet. Possibly the reason for the dinosaur extinction - Before better testing was available it was widely thought that the meteor that struck this area caused the extinction of the dinosaurs.
It is now known that the meteor that struck current day Manson, IA happened 20 million years before the dinosaurs became extinct. The American Nobel laureate Luis Alvarez, who became gripped with the problem of explaining dinosaur extinctions after a conversation with his geologist son Walter. It was really quite a presumptuous request. They were asking Asaro to devote months to making the most painstaking measurements of geological samples merely to confirm what seemed entirely self-evident to begin with—that the thin layer of clay had been formed as quickly as its thinness suggested.
Certainly no-one expected his survey to yield any dramatic breakthroughs. It ran for minutes and we could see we were getting interesting results, so we stopped it and had a look. The results were so unexpected, in fact, that the three scientists at first thought they had to be wrong. The amount of iridium in the Alvarez sample was more than three hundred times normal levels—far beyond anything they might have predicted. Tests on other samples—from Denmark, Spain, France, New Zealand, Antarctica—showed that the iridium deposit was worldwide and greatly elevated everywhere, sometimes by as much as five hundred times normal levels.
Clearly something big and abrupt, and probably cataclysmic, had produced this arresting spike. After much thought, the Alvarezes concluded that the most plausible explanation—plausible to them, at any rate—was that the Earth had been struck by an asteroid or comet. The idea that the Earth might be subjected to devastating impacts from time to time was not quite as new as is now sometimes suggested.
As far back as , a Northwestern University astrophysicist named Ralph B. Baldwin had suggested such a possibility in an article in Popular Astronomy magazine. He published the article there because no academic publisher was prepared to run it. Even among palaeontologists it was not unknown. In a professor at Oregon State University, M. A year before the Alvarezes announced their controversial theory, Hollywood provided an unwitting reminder that the idea of devastating impacts from space was hardly new.
In fact, it had been around since But it did. It was received everywhere, but particularly in the palaeontological world, as an outrageous heresy. Walter was a geologist specializing in palaeomagnetism, Luis was a physicist and I was a nuclear chemist.
And now here we were telling palaeontologists that we had solved a problem that had eluded them for over a century. But there was also something much deeper and more fundamentally abhorrent in the impact theory. The belief that terrestrial processes were gradual had been elemental in natural history since the time of Lyell.
By the s, catastrophism had been out of fashion for so long that it hadbecome literally unthinkable. Nor did it help that Luis Alvarez was openly contemptuous of palaeontologists and their contributions to scientific knowledge.
One of the most vigorous opponents was Charles Officer of Dartmouth College. He insisted that the iridium had been deposited by volcanic action even while conceding in a newspaper interview that he had no actual evidence of it. As late as , more than half of all American palaeontologists contacted in a survey continued to believe that the extinction of the dinosaurs was in no way related to an asteroid or cometary impact. Enter Eugene Shoemaker. Shoemaker had an Iowa connection—his daughter-in-law taught at the University of Iowa—and he was familiar with the Manson crater from his own studies.
Thanks to him, all eyes now turned to Iowa. Geology is a profession that varies from place to place. In Iowa, a state that is flat and stratigraphically uneventful, it tends to be comparatively serene. There are no alpine peaks or grinding glaciers, no great deposits of oil or precious metals, not a hint of a pyroclastic flow. No-one now can remember quite when, still less why, the state geologists were placed in an academic facility, but you get the impression that the space was conceded grudgingly, for the offices are cramped and low-ceilinged and not very accessible.
When being shown the way, you half expect to be taken out onto a roof ledge and helped in through a window. Ray Anderson and Brian Witzke spend their working lives up here amid disordered heaps of papers, journals, furled charts and hefty specimen stones. Geologists are never at a loss for paperweights. I asked them about Gene Shoemaker, a man who seems to have been universally revered. Even with his support, it took two years to get it up and running.
Eugene Shoemaker was one of the first scientists to be convinced of the potential—and in the long run inevitable—dangers of comets and asteroids colliding with Earth. Certainly more than our budget would allow. The declaration attracted a good deal of press attention but was unfortunately premature. A more careful examination of the data revealed that Manson was not only too small, but also nine million years too early. He shrugged. The search moved elsewhere. Hildebrand travelled to the site and decided fairly swiftly that they had their crater.
The devastation was far greater than most scientists had expected. Conveniently, a natural test of the theory arose soon after when the Shoemakers and Levy discovered Comet Shoemaker-Levy 9, which they soon realized was headed for Jupiter. For the first time, humans would be able to witness a cosmic collision—and witness it very well, thanks to the new Hubble Space Telescope. Most astronomers, according to Curtis Peebles, expected little, particularly as the comet was not a coherent sphere but a string of twenty-one fragments.
The impacts began on 16 July , went on for a week and were bigger by far than anyone—with the possible exception of Gene Shoemaker—expected. One fragment, known as Nucleus G, struck with the force of about six million megatonnes—seventy-five times all the nuclear weaponry in existence.
Nucleus G was only about the size of a small mountain, but it created wounds in the Jovian surface the size of Earth. It was the final blow for critics of the Alvarez theory. Luis Alvarez never knew of the discovery of the Chicxulub crater or of the Shoemaker-Levy comet, as he died in Shoemaker also died early On the third anniversary of the Jupiter collision, he and his wife were in the Australian outback, where they went every year to search for impact sites.
On a dirt track in the Tanami Desert—normally one of the emptiest places on Earth—they came over a slight rise just as another vehicle was approaching. Shoemaker was killed instantly, his wife injured.
Some of his ashes were sent to the Moon aboard the Lunar Prospector spacecraft. The rest were scattered around Meteor Crater.
Other craters are larger—notably, Chesapeake Bay, which was recognized as being an impact site in —but they are either offshore or deformed. I asked them how much warning we would receive if a similar hunk of rock were coming towards us today. The likelihood is that such a visitation would take us completely by surprise.
How hard an impactor hits depends on a lot of variables—angle of entry, velocity and trajectory, whether the collision is head-on or from the side, and the mass and density of the impacting object, among much else—none of which we can know so many millions of years after the fact.
But what scientists can do—and Anderson and Witzke have done—is measure the impact site and calculate the amount of energy released. Latest posts by Curious Craig see all. Historic Sunken Gardens — St. I love comments, let me know what you think! Cancel reply.
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