Sensations from the world
The world of meteorites is a world of sensations,
some of these sensations we refered already on the pages origin and records. For the popular press however, usually it is more worth mentioning, when a little meteorite causes earthly damage, than when a large cosmic lump is found in the desert, or if it turns out that it comes from the Moon or from Mars. The Mars meteorite of Nakhla, that fell in 1911 in Egypt in several pieces on Earth, from the beginning produced in the press more fuss by the fact, that one of its fragments killed a dog than by the later discovery, that it is a fragment from our red neighbour planet!
Other messages are quite amusing: for example on 10th December 1984, a 1,5 kg heavy stony meteorite demolished as a sort of cosmic mail a mailbox in Claxton, Georgia, USA. On april 7th 1990 in Glanerbrug, Netherlands, a 670 g heavy meteorite tumbled into the middle of a kitchen of a house after it had punctured the roof. And especially well known became the meteorite of Peekskill, New York, USA, who after it pierced through the trunk of a parking, red Chevy Malibu on 9th October 1992 got stuck unneath in the asphalt. The culprit was even filmed on its way to the crime scene by an amateur. Fragments of the 12 kg heavy Chondrite today are dealed in collector circles for more than 200 $/g, and the Chevy was an eye-catcher on numerous fairs and exhibitions in Germany, Switzerland, Japan, France and the USA.
Nicht immer geht der Fall eines Meteoriten so glimpflich ab. Und auch wenn es bis heute keinen nachgewiesenen Fall gibt, in dem ein Mensch durch einen Meteorit erschlagen wurde, hat es in der Vergangenheit doch immer wieder beängstigende Impaktereignisse gegeben, von denen zahlreiche grosse Meteoritenkrater in aller Welt Zeugnis ablegen. Wenn man z.B. heute die schwäbische Alb bereist und dort das friedliche Städtchen Nördlingen inmitten einer etwa 25 km grossen Senke liegen sieht, ahnt man kaum, dass es sich bei dieser als Nördlinger Ries bekannten Struktur um einen gewaltigen Impaktkrater handelt.
Vor etwa 15 Millionen Jahren ging hier ein fast ein Kilometer grosser Meteorit mit einer Geschwindigkeit von 70.000 km/h nieder, drang kilometertief in die Erde ein und riss mit der Energie von 250.000 Hiroshima-Bomben einen inneren Krater von über zwölf Kilometern Durchmesser aus der Albhochfläche. Alles Leben im Umkreis von über hundert Kilometern wurde augenblicklich durch eine Schockwelle vernichtet, und gewaltige Wolken aus verdampftem Gestein legten sich über grosse Teile Mitteleuropas. Das Gestein kondensierte zu einer glasartigen Masse, die z.B. über der heutigen Tschechei abregnete, wo man heute die sogenannten Moldavite finden kann, ein grünes, durchsichtiges Gesteinsglas, das meist in Form verwitterter Tropfen gefunden und gelegentlich zu Schmuck verarbeitet wird.
Die Ausmasse und Folgen von kosmischen Einschlägen von der Grössenordnung des Ries-Impakts sind nahezu unvorstellbar und lassen filmische Horrorszenarien á la Armaggedon oder Deep Impact im Vergleich wie Sandkastenspiele erscheinen. Echten Impakt-Ereignissen dieser Kategorie folgte stets eine Art nuklearer Winter, in dem die Sonne viele Jahre lang durch die dicken Staubwolken verdunkelt wurde und kaum mehr die Erde erreichte. Was folgte, war ein Massensterben unvorstellbaren Ausmaßes, und man geht heute davon aus, dass auch das Ende der Dinosaurier und der Tierwelt der Kreidezeit durch einen kosmischen Treffer verursacht wurde, der das Ries-Ereignis um einiges übertraf!
The fall of a meteorite does not always get off so lightly. And also if there is no proved case until today, where a person got killed by a meteorite, there have been frightening impact cases in the past again and again, of which numerous large meteorite craters in the whole world bear testimony. If nowadays one travels in the Swabian Albs and there sees for example the peaceful village Nördlingen in the middle of an about 25 km large depression, one hardly suspects, that this as Nördlinger Ries well known structure is a powerful impact crater one is dealing with.
About 15 millions years ago here an almost one kilometer large meteorite with a speed of 70.000 km/h went down, penetrated one kilometer deep into the earth and tore an internal crater of more than twelve kilometers diameter with the energy of 250.000 Hiroshima-bombs out of the alb highplane. All life in the vicinity of more than hundred kilometers got immediately destroyed by a shock wave, and powerful clouds of evaporated rock went down over large parts of Central Europe. The rock condensed to a glassy mass, which for example rained down over the nowadays Czechoslowakia, where one can find these days the socalled Moldavites, a green, transparent rock glass that is found usually in form of weathered drops and occasionally is made into jewelry.
The extents and sequences of cosmic impacts of the order of magnitude of the Ries-impact are almost unimaginable and in comparison, film horrorszenes á la Armaggedon or Deep Impact appear like sand box games. Always after real impact-events of this category a kind of nuclear winter followed, when the Sun was darkened for many years by thick dust clouds, and scarcely reached the Earth any more. What followed, was a mass dying of an unimaginable extent, and one is assuming today that also the end of the Dinosaurs and the animal world of the chalk time was caused by a cosmic hit, which surpassed the Ries-event a couple of times!
It was known since long, that at the transition between the geological era of Chalk and Tertiary about 65 millions years ago, an unimaginable catastrophe must have happened, for at that time not only the Dinosaurs suddenly were extincted after they had controlled the earth for almost 150 millions years: over three-quarters of all that time well known animals and plant types were extinguished within short time. In the beginning one assumed, that powerful volcano outbreaks were responsible for that mass dying, but in 1978 Italian researchers, who examined the geological dividing layer between chalk and tertiary, discovered a centimeter-thick redbrown layer of clay, something quite sensational. This layer contained large quantities of the noble metal Iridium, on Earth very rare, but in meteorites usually occurs in thousand times higher concentration. Is it that the impact of a giant meteorite has put an end to the giants of prehistoric times?
In the beginning this daring theory was rejected by many scientists, mainly because no impact crater of corresponding size and suitable age was known. Only in 1990 researchers discovered at the coast of Yukatan, Mexico, a craterformlike structure with a diameter of about 280 kilometers. Until then it had been unrecognized, because over half of the crater lies on the ground of the gulf of Mexico and the landpart of the structure in the course of millions of years was filled with sediments and therefore superficially is no longer visible. The age determination of the newly discovered Chicxulub-crater yielded a sensation: here 65 millions years ago had hit a powerful meteorite with more than 10 kilometers diameter and the power of 5 billions megatons TNT - say over 10 millions Hiroshima-bombs -, enough destruction power to throw the Earth into a decades long winter and to extinguish almost all life!
Today one knows, that such mass dying through the impact of powerful meteorites happened in the history of the Earth again and again, and one is concerned by the possibility of such an impact in our time. Although one meanwhile knows several hundred objects with a diameter of one kilometer and more, that cross our Earth's orbit and could collide some day with us, a far greater danger comes from smaller objects with a diameter of about hundred meters. First of all there are many more such small asteroids, and secondly they can be discovered only with difficulty through telescopes or with radar. Therefore a prediction is almost impossible. In the last century, at least two of such impacts happened - 1908 at the rocky Tunguska, Siberia, and 1930 in the vicinity of Rio Curuca, Brazil -, which however occured fortunately in uninhabited zones. If they had hit a city or a populated zone, their effect would have been more devastating than the dropping of a hydrogen bomb with the explosive power of 20 megatons of TNT!
However there are also scientific sensations from the world of meteorites, letting them appear in an entirely different light: not as potential destroyers, but rather - on the opposite - as lifebringers. At the end of the 19th century one has already found water and traces of organic substances in many carbonaceous Chondrites, but this discovery was dismissed until the sixties of the last century as earthly pollution for not having to think earnestly about possible consequences for our world- and selfview. So in september 1969 in Murchison, Australia, a further carbonaceous Chondrite fell, which safely could be recovered before each possibility of an earthly contamination, and delivered science in consequence more data, than for good many was dear.
In the Murchison meteorite one found not only over 10% bound water, but rather also complex hydrocarbons and the constituents of all life: amino acids. While we commonly know on earth 22 amino acids, that are involved in all life processes, from of the Murchison meteorite were isolated more than 230 different amino acids, which until today give science numerous riddles. Most researchers don't believe in a biogene origin of the organic substances, but assume more and more, that carbonaceous Chondrites in the genesis of life on our Earth played a paramount, if not quite decisive role, in that they brought not only water, but rather also all materials necessary for life as well as cosmic spermes onto the chaste, receptive Earth.
If this is true, it could be that life on our Earth is not quite as unique, as many of us still believe. If the substances necessary for life emerge in the universe and are planted by comets and meteorites on receptive planets for further development, the same development could have happened at many places. And it was a meteorite, that brought this shocking possibility into the area of probability and made the president of the USA, Bill Clinton, at a public speech in august 1996 think about the possibility of life on our neighbour planet Mars.
The reason for this speech were the results of an american research group, whose various investigations were, since their find in 1984, trickered by the antarctic Mars meteorite ALH 84001. They had found in this meteorite small microscopic fossils, that resembled earthly bacteria, as well as minutely small magnetite crystals, being produced in this form on earth only by certain bacteria. Moreover one found traces of PAHs, complex organic substances, that indicate on life on mars.
This find caused hot debates in scientist circles, lasting until today. One party tried to prove with all means that the research results are either fallacies based on earthly contamination or inorganic processes, that are falsely interpreted as life traces. But more and more researchers connect themselves with the second fraction, which carefully tries to take the possibility of a primitive life on Mars into consideration, which maybe exists until now. This controversy explains at least the in the last years revived interest in manned expeditions to our neighbour planet, that maybe will give an answer on the question to us, that torments humanity since ancient times: are we alone in the cosmos?