There is though, another agent which could destroy civilization and do great harm to the environment, a large consignment of elements from space. Such deliveries are not as uncommon as was previously thought, particularly during the past twelve thousand years. Much evidence suggests that humanity witnessed, and was affected by, the break-up of a very large comet over this time period. Astronomers, using data gathered on meteor showers, have established that this debris had about the same orbital characteristics five thousand years ago as it has today. The stuff orbits the Sun in roughly three and a third years and while doing so crosses our planet's orbital path twice. Clearly the potential for collision is real and has been realized a number of times in the past--most recently in the eight year of this century.
Study of the "Tunguska event" has shed considerable light on the subject of impact phenomena. Interestingly this illumination would probably be much weaker were it not for the value of nickel and other metals that often comprise a meteorite. The newly established Soviet government was strapped for funds in 1921; warfare had ravaged their homeland over the previous six years and it was now time to rebuild. Any plan that held promise of producing a lot of rubles quickly must have seemed attractive to Soviet officials. American geologist/mine engineer Daniel Barringer's quest to extract the five to fifteen million tons of meteorite metal that, he believed, was buried beneath "meteor Crater" in Arizona had attracted considerable attention about the world. The prospect of finding over a billion dollars worth of metal in the bottom of a hole was quite intriguing--a natural "pot of gold" story. Also, much scientific debate had been sparked by Barringer's activity. Most geologists favored a more down to earth explanation of this crater--the planet had simply blown off a bit of steam there.
Barringer had finished his first boring episode in July of 1908, totally oblivious (as was most of the world) to the fearful excitement that still gripped those who had witnessed a terrifying arrival of space debris only weeks earlier. Though the outside world would remain ignorant of the Tunguska fall for two decades, there were reports, printed in several Russian newspapers, of some unusual phenomena which occurred in remote Siberia on the last morning of June (1908). One of these stories must have later seemed extremely attractive to the cash poor Soviets. This particular report stated that all the commotion had been caused by the landing of a large meteoroid which fell very close to a railway. The story indicated that the meteorite was only partially buried and might be as much as six cubic sagines in size. Six cubit sagines translates into a twelve foot, nine inch cube of meteorite material--a hunk of potentially valuable stuff that could be hoisted onto a railcar and pulled to wherever. Barringer was drilling away again in 1921 and largely due to the publicity this activity received, it was now widely known that meteorites often contained, in addition to nickel, diamonds, platinum, gold and other materials of high monetary value. These baubles from space could also fetch a good price from museum collectors who would pay dearly to keep such valuable pieces of information out of a furnace. In light of the circumstances, it is easy to see why the Soviets chose to fund, as one of their first scientific expeditions, a search for meteorites.
As it turned out the only people in North American or the Soviet Union that made a lot of money from a meteorite in the twenties were those who had no idea they were digging up space debris--the Canadians mining at Sudbury.
The real value of these searches proved to be in the wealth of information uncovered. Much to Barringer's disappointment it was learned that a relatively small object would excavate a lot of earth and rock as it slammed into the planet. This prospector saw his five to fifteen million ton jackpot shrink at least ten fold. Furthermore, he was informed that most of the one-and-a-half, to half-million ton mass which created his crater had been liquefied in the process. This meant that what celestial material had not splashed out of the feature was widely distributed within it, making a profitable mining operation very doubtful. Barringer did not accept astronomer Forest Ray Moulton's conclusions, however, he could not disprove them. Financial backers of the mining project, who had commissioned Moulton's study, withdrew their support. Barringer, whose tenacious spirit helped prove that large craters could result form meteoroid impact, died of a stroke after three months of heated debate over Moulton's 1929 papers. This researcher/prospector contributed much to science over his sixty-nine years.
Soviet scientist Leonid Kulik was not so much frustrated by what his research was revealing as he was perplexed. Though the news clip which justified Kulik's 1921 expedition to remote Siberia had proven to be almost totally inaccurate, the trip had been intriguing. Descriptions given by actual witnesses of the 1908 event piqued Kulik's curiosity to the point where he had to find out what really happened in this sparsely populated region of the world. This researcher dug in, and after six years of fact gathering he finally persuaded the Soviet Academy of Science that it was time for another expedition.
Much of the information Kulik had been compiling came from fellow researchers doing work in that part of Siberia. Most intriguing were stories relayed back from scientists working among the native Tungus people. This had posed somewhat of a problem for Kulik, as few scientists in the academy gave credence to tales told by those they considered to be primitive, backward people. What finally tipped the scales in Kulik's favor was a report prepared by a former head of the Inkutch Observatory, A.V. Vognesensky. Vognesensky combined the data Kulik had gathered with 1908 seismic data recorded at Irkutsk and concluded that:
. . . it is highly probable that the future investigator of the spot where the Khatanga [Stony Tunguska] meteorite fell will find something very similar to the meteorite crater of Arizona; i.e., from 2 to 3 kilometers around he will find a mass of fragments that were separated from the main nucleus before it fell and during its fall. The Indians of Arizona still preserve the legend that their ancestors saw a fiery chariot fall from the sky and penetrate the ground at the spot where the crater is; the present-day Tungusi people have a similar legend about a new fiery stone. This stone they stubbornly refused to show to the interested Russians who were investigating the matter in 1908. However that may be, the search for and investigation of the Khatanga meteorite could prove a very profitable subject of study, particularly if this meteorite turned out to belong to the iron class.
This is why Kulik was a bit dumfounded when, in 1927, he actually found the spot he had sought. The devastation was quite obvious; over seven hundred square miles of dense Siberian forest had been scorched and flattened. There was, however, no crater.
Kulik's find revealed that colliding space debris could do a great deal of damage yet leave little long-term detectable evidence to indicate that an impact had occurred. Some implications of this fact were recognized by a few investigators almost immediately. Astronomer C.P. Olivier, writing of Kulik's discovery for Scientific American, stated in the July 1928 issue:
In looking over this account, one has to admit that many accounts of events in old chronicles that have been laughed at as fabrications are far less miraculous than this one, of which we seem to have undoubted confirmation. Fortunately for humanity, this meteoric fall happened in a region where there were no inhabitants precisely in the affected area, but if such a thing could happen in Siberia there is no known reason why the same could not happen in the United States.
Olivier's statement would have certainly invoked a nod from any reader who had perused an essay published the year before by Franz Xavier Kugler. Kugler was a Jesuit priest who had devoted much of his life to the study of ancient cuneiform astronomical tablets. Like other philologists, Kugler had earlier in his career decided that some of the unearthed tablets he deciphered were purely fictional. This scholar's 1927 essay, Sybillinischer Sternkampf und Phaethon in naturgeschichtlicher Beitrage (The Sybilline Battle of the Stars and Phaethon Seen as Natural History), was published two years before his death. Apparently the emerging realization of how destructive a meteoroid impact could be, combined with his life-long study of ancient astronomical texts, prompted Kugler to re-evaluate his earlier interpretation of some of the clay tablets deciphered by him. The importance of Kugler's work stems from the fact that he was reading unearthed documents, not handed down tales. Researchers are, understandably, reluctant to put much faith in stories that have been passed along over many generations. Both the Sybylline Oracles and the story of Phaethon fall into this category. Though other sources establish these traditions as ancient, no really early written version of these works has been found. By pointing out features that such stories had in common with unearthed cuneiform texts, Kugler was able to shed some light on the original core of these tales. In Kugler's opinion, the destructive impact, around thirty-five hundred years ago, of a sun-like meteor, which he found chronicled on clay tablets, provided the inspiration for the Sibylline Battle of the Stars and the Phaethon legend.
Actually, as we learn more of the phenomena an impact event is capable of producing, many ancient accounts are appearing less incredible. For instance, several cultures about the world have retained legends which associate cold weather with fire coming down from the sky. Only a decade ago if any credence was given to such a tale, the assumption would have been that the story was inspired by vulcanism. While it is certainly possible that some legends do stem from volcanic activity it is no longer "scientific" to make such an assumption. Researchers now know that an impact event could produce a darkening of the sky and so cause a steep drop in temperature.
The Sibylline Oracles employ less metaphor than many ancient accounts and so provide some rather succinct lines for the reader to ponder:
And then in his anger the immortal God who dwells on high shall hurl from the sky a fiery bolt on the head of the unholy: and summer shall change to winter in that day. And then great woe shall befall mortal men: for He that thunders from on high shall destroy all the shameless, with thunderings and lightnings and burning thunderbolts upon his enemies, and shall make an end of them for their ungodliness, so that the corpses shall lie on the earth more countless than the sand.
The above is from a 1918 translation by H.N. Bate. Reverend Bate, as did most scholars of that time, perceived these lines as nothing more than eschatological embellishment of the apocalyptic theme. The phrase, "and summer shall change to winter in that day," did not need to make sense from his point of view; Bate simply noted that in another version (Book VIII) of these oracles, a parallel passage has God changing winter to summer. The interesting factor here is that to someone with no knowledge of impact phenomena, the notion that it should become cold as a result of God throwing fire from heaven is absurd. From a "logical" perspective it would be easy to assume that a scribal error produced this nonsense and a simple swap of word position would correct it. In a translation by Milton S. Terry, published in 1899, a reader can thumb to Book V and find essentially the same lines as those quoted above from Bates' translation. The only real difference in Terry's version has: "And in the place of winter there shall be in that day summer." This "correction" was probably not made by Professor Terry but by a Venetian scholar, Aloisius Rzach. Terry based his English translation on Rzach's Greek version, published in 1891, because it was in his words, "The latest and most improved edition of the Greek text of the twelve books now extant . . . ." However, Terry does caution his readers that Rzach's ". . . work has not escaped criticism, especially on account of its numerous conjectural emendations, . . ."
The assumption or premise that our ancestors were only referring to phenomena which we, also, are familiar with has produced considerable distortion in our view of the past. Consider the term thunder-bolt. A large stony meteoroid will often break up violently in the atmosphere. If the object is large enough to reach into the lower atmosphere, an observer will see a blinding flash of light followed by a loud crash of thunder. Often a large dark cloud composed of oxides of nitrogen and debris from the object will appear. This cloud can be highly charged and so cause conventional lightning to ensue. Scientists call such an arrival a bolide. Technically the Tunguska object falls into this classification because its energy was released several miles above our planet's surface. A problem is that most people who have translated ancient texts had never witnessed a large bolide and until fairly recently, few, if any, would be aware that such a phenomenon could occur. A term like thunder-bolt, to people unfamiliar with impact phenomena, easily equates with lightning bolt. As a result, many ancient accounts of impact phenomena have been read as descriptions of jolly good storms.
At present the academic community is in the process of a major alteration of world view. The picture of a placid, slowly changing environment is being replaced by the image of a biosphere periodically thrown into chaos by major impact events. Though debate continues on the degree of influence, it is now widely accepted that past collisions with extraterrestrial objects have played a role (likely a major one) in biological evolution. What has yet to be adequately investigated is the part past impacts have played in human social evolution.
The assertion that cosmic collisions have affected society is not new. Plato, in his Timeaus, makes it plain that he believed impacts to be responsible for losses of history. By way of dialogue Plato has an aged Egyptian priest inform his Greek visitor, Solon, that the story of Phaethon, known to the Greeks as a fable, is in reality, true, as " . . . it expresses the mutation of the bodies revolving in the heavens about the earth; and indicates that, after long periods of time, a destruction of terrestrial natures ensues from the devastations of fire." The priest next points out that the Gods (heavenly bodies) also cause great floods which take the lives of many people. He then explains to Solon that, due to the Nile, Egypt has fared better than most nations and so has retained its ancient history, "[w]hile, on the contrary, you and other nations commit only recent transactions to writing, and to other inventions which society has employed for transmitting information to posterity; and so again, at stated periods of time, a certain celestial defluxion rushes on them like a disease; from whence those among you who survive are both destitute of literary acquisitions and the inspiration of the Muses. Hence it happens that you become juvenile again, and ignorant of the events which happened in ancient times, as well among us as in the regions which you inhabit."
Until very recently, there was little evidence to support Plato's contention, particularly his assertion that these events occurred "at stated periods of time." What has now moved the words of this old Greek philosopher from the improbable to plausible realm is a contemporary awareness of the numerous large objects that cross our planet's path--especially the debris mentioned earlier that is associated with comet Encke.
British astronomers Victor Clube and Bill Napier present, in The Cosmic Serpent (1982), a strong astronomical based argument which contends that, due to its orbital characteristics, the progenitor of comet Encke quite likely caused humanity a great deal of grief in the past. How large this comet was when it first fell into an Earth-orbit-crossing path is not known. It is possible that this object had more in common with a beast like Chiron than it did with the normally small, long-period comets. Chiron's size is about one-hundred miles across. It presently has an unstable fifty-one year orbit which keeps it between the paths of Saturn and Uranus. The object has exhibited comet-like activity to astronomers and because Chiron's orbit is not stable it could be pulled into our region of the solar system a few thousand years from now.
It is difficult to truly appreciate the visual phenomena that such a large object could produce as it neared the furnace of our solar system. Gases from such an object might produce a coma as large as the Sun and a tail which would span the orbits of the inner planets. In close proximity to Earth, the size of such an apparition would make the Sun and Moon appear as dwarfs. Combined evidence suggests that our ancestors witnessed such mega-comet activity and were influenced psychologically, as well as physically, by the ensuing phenomena such a large interloper could, and apparently did, produce.
One way the reader can realize the collective ignorance, and yet appreciate how fast things are changing in this area of research, is by comparing the number of objects Clube and Napier associated with comet Encke in 1982 to the number known presently. In The Cosmic Serpent, the authors list only one object, Hephaistos, as having once been part of the still active comet Encke. Hephaistos was discovered in 1978 and is one of the largest Earth-orbit-crossing objects found so far. Its six mile diameter (about the same as the hypothetical dinosaur slayer) is actually larger than comet Encke's estimated girth. As of now (late 1988), five objects in addition to Encke are identified with this group, with two more orbiting bodies seen as likely members.
The rapid population rise of recognized objects in the Encke group is a result of a stepped up effort to locate Earth-orbit-crossing objects in general. Prior to the 1979 discovery of hard evidence which indicated a link between mass extinction and impact generated phenomena, few researchers were working in this area. Most astronomers were studying features far removed from our solar system such as black holes and other galaxies, while geologists and paleontologists, in the main, were comfortable with the long held idea of an Earth that changed very slowly. What is presently taking place constitutes a change of view as radical as the altered picture which came from proving the Sun does not orbit about the Earth. Naturally, not all researchers are happy with what is transpiring--abandoning long-held assumptions is not pleasant, particularly when these beliefs served as corner stones to your research. This is though, where the true value of the scientific method comes into play. Once enough evidence is found to show a prior assumption false, that earlier belief will become passé, no matter how familiar and comfortable it had been. Understandably, a bit of verbal battling takes place before there is a general acceptance of a new world view and this process of hashing it out can appear quite confusing to a casual observer. One article might convey to the reader that, though impacts can cause mass extinction, our time period falls safely between such periodically recurring events so there is no reason for us to worry. Another paper might state: Yes major impacts occur, but they do not cause extinction because . . . Actually, a consensus has emerged among scientists who are in the forefront of this research. These investigators agree that mass extinction has been caused by impact phenomena, and that major impact events increase in frequency at thirty to thirty-three million year intervals. They also concur with evidence which indicates that the last bombardment episode spanned a few million years, around a date which occurred thirty-four million years ago. A recent (over the past two million years) rise in the rate of crater formation combined with the evidence for periodicity leads these scientists to conclude that we are presently within such a bombardment episode. Their contention is further strengthened by the contemporary presence of a larger than normal population of Earth-orbit-crossing objects. Stated simply, these researchers agree that the chance of a major impact happening in the near future is much, much greater than it was thought to be only a decade ago. This also means, of course, the probability that there have been fairly recent past impacts is also greater. In fact, the orbital characteristics of debris associated with comet Encke basically guarantees that significant collisions have taken place within the last fifteen thousand years.