was odd too。 it wasalmost as soft as rainwater。 naturally occurring soft water had never been found in iowabefore。
though manson鈥檚 strange rocks and silken waters were matters of curiosity； forty…oneyears would pass before a team from the university of iowa got around to making a trip to themunity； then as now a town of about two thousand people in the northwest part of thestate。 in 1953； after sinking a series of experimental bores； university geologists agreed thatthe site was indeed anomalous and attributed the deformed rocks to some ancient； unspecifiedvolcanic action。 this was in keeping with the wisdom of the day； but it was also about aswrong as a geological conclusion can get。
the trauma to manson鈥檚 geology had e not from within the earth； but from at least 100million miles beyond。 sometime in the very ancient past； when manson stood on the edge of ashallow sea； a rock about a mile and a half across； weighing ten billion tons and traveling atperhaps two hundred times the speed of sound ripped through the atmosphere and punchedinto the earth with a violence and suddenness that we can scarcely imagine。 where mansonnow stands became in an instant a hole three miles deep and more than twenty miles across。
the limestone that elsewhere gives iowa its hard mineralized water was obliterated andreplaced by the shocked basement rocks that so puzzled the water driller in 1912。
the manson impact was the biggest thing that has ever occurred on the mainland unitedstates。 of any type。 ever。 the crater it left behind was so colossal that if you stood on oneedge you would only just be able to see the other side on a good day。 it would make the grandcanyon look quaint and trifling。 unfortunately for lovers of spectacle； 2。5 million years ofpassing ice sheets filled the manson crater right to the top with rich glacial till； then graded itsmooth； so that today the landscape at manson； and for miles around； is as flat as a tabletop。
which is of course why no one has ever heard of the manson crater。
at the library in manson they are delighted to show you a collection of newspaper articlesand a box of core samples from a 1991鈥�92 drilling program鈥攊ndeed； they positively bustle toproduce them鈥攂ut you have to ask to see them。 nothing permanent is on display； andnowhere in the town is there any historical marker。
to most people in manson the biggest thing ever to happen was a tornado that rolled upmain street in 1979； tearing apart the business district。 one of the advantages of all thatsurrounding flatness is that you can see danger from a long way off。 virtually the whole townturned out at one end of main street and watched for half an hour as the tornado came toward them； hoping it would veer off； then prudently scampered when it did not。 four of them； alas；didn鈥檛 move quite fast enough and were killed。 every june now manson has a weeklong eventcalled crater days； which was dreamed up as a way of helping people forget that unhappyanniversary。 it doesn鈥檛 really have anything to do with the crater。 nobody鈥檚 figured out a wayto capitalize on an impact site that isn鈥檛 visible。
鈥渧ery occasionally we get people ing in and asking where they should go to see thecrater and we have to tell them that there is nothing to see；鈥潯ays anna schlapkohl； the town鈥檚friendly librarian。 鈥渢hen they go away kind of disappointed。鈥潯owever； most people；including most iowans； have never heard of the manson crater。 even for geologists it barelyrates a footnote。 but for one brief period in the 1980s； manson was the most geologicallyexciting place on earth。
the story begins in the early 1950s when a bright young geologist named eugeneshoemaker paid a visit to meteor crater in arizona。 today meteor crater is the most famousimpact site on earth and a popular tourist attraction。 in those days； however； it didn鈥檛 receivemany visitors and was still often referred to as barringer crater； after a wealthy miningengineer named daniel m。 barringer who had staked a claim on it in 1903。 barringer believedthat the crater had been formed by a ten…million…ton meteor； heavily freighted with iron andnickel； and it was his confident expectation that he would make a fortune digging it out。
unaware that the meteor and everything in it would have been vaporized on impact； hewasted a fortune； and the next twenty…six years； cutting tunnels that yielded nothing。
by the standards of today； crater research in the early 1900s was a trifle unsophisticated； tosay the least。 the leading early investigator； g。 k。 gilbert of columbia university； modeledthe effects of impacts by flinging marbles into pans of oatmeal。 （for reasons i cannot supply；gilbert conducted these experiments not in a laboratory at columbia but in a hotel room。）somehow from this gilbert concluded that the moon鈥檚 craters were indeed formed byimpacts鈥攊n itself quite a radical notion for the time鈥攂ut that the earth鈥檚 were not。 mostscientists refused to go even that far。 to them； the moon鈥檚 craters were evidence of ancientvolcanoes and nothing more。 the few craters that remained evident on earth （most had beeneroded away） were generally attributed to other causes or treated as fluky rarities。
by the time shoemaker came along； a mon view was that meteor crater had beenformed by an underground steam explosion。 shoemaker knew nothing about undergroundsteam explosions鈥攈e couldn鈥檛： they don鈥檛 exist鈥攂ut he did know all about blast zones。 oneof his first jobs out of college was to study explosion rings at the yucca flats nuclear test sitein nevada。 he concluded； as barringer had before him； that there was nothing at meteorcrater to suggest volcanic activity； but that there were huge distributions of other stuff鈥攁nomalous fine silicas and magnetites principally鈥攖hat suggested an impact from space。
intrigued； he began to study the subject in his spare time。
working first with his colleague eleanor helin and later with his wife； carolyn； andassociate david levy； shoemaker began a systematic survey of the inner solar system。 theyspent one week each month at the palomar observatory in california looking for objects；asteroids primarily； whose trajectories carried them across earth鈥檚 orbit。
鈥渁t the time we started； only slightly more than a dozen of these things had ever beendiscovered in the entire course of astronomical observation；鈥潯hoemaker recalled some yearslater in a television interview。 鈥渁stronomers in the twentieth century essentially abandonedthe solar system；鈥潯e added。 鈥渢heir attention was turned to the stars； the galaxies。鈥�
what shoemaker and his colleagues found was that there was more risk out there鈥攁 greatdeal more鈥攖han anyone had ever imagined。
asteroids； as most people know； are rocky objects orbiting in loose formation in a beltbetween mars and jupiter。 in illustrations they are always shown as existing in a jumble； butin fact the solar system is quite a roomy place and the average asteroid actually will be abouta million miles from its nearest neighbor。 nobody knows even approximately how manyasteroids there are tumbling through space； but the number is thought to be probably not lessthan a billion。 they are presumed to be planets that never quite made it； owing to theunsettling gravitational pull of jupiter； which kept鈥攁nd keeps鈥攖hem from coalescing。
when asteroids were first detected in the 1800s鈥攖he very first was discovered on the firstday of the century by a sicilian named giuseppi piazzi鈥攖hey were thought to be planets； andthe first two were named ceres and pallas。 it took some inspired deductions by theastronomer william herschel to work out that they were nowhere near planet sized but muchsmaller。 he called them asteroids鈥攍atin for 鈥渟tarlike鈥濃�攚hich was slightly unfortunate asthey are not like stars at all。 sometimes now they are more accurately called planetoids。
finding asteroids became a popular activity in the 1800s； and by the end of the centuryabout a thousand were known。 the problem was that no one was systematically recordingthem。 by the early 1900s； it had often bee impossible to know whether an asteroid thatpopped into view was new or simply one that had been noted earlier and t