sign in sign up
<<
Home , Iridium anomaly, Neocatastrophism, Saurischia

The Proceedings of the International Conference on Creationism

Volume 4 Print Reference: Pages 241-252 Article 18

1998

The Impact at the /Tertiary Boundary

Thomas Fritsche

Follow this and additional works at: https://digitalcommons.cedarville.edu/icc_proceedings

DigitalCommons@Cedarville provides a publication platform for fully open access journals, which means that all articles are available on the Internet to all users immediately upon publication. However, the opinions and sentiments expressed by the authors of articles published in our journals do not necessarily indicate the endorsement or reflect the views of DigitalCommons@Cedarville, the Centennial Library, or Cedarville University and its employees. The authors are solely responsible for the content of their work. Please address questions to [email protected].

Browse the contents of this volume of The Proceedings of the International Conference on Creationism.

Recommended Citation Fritsche, Thomas (1998) "The Impact at the Cretaceous/Tertiary Boundary," The Proceedings of the International Conference on Creationism: Vol. 4 , Article 18. Available at: https://digitalcommons.cedarville.edu/icc_proceedings/vol4/iss1/18 THE IMPACT AT THE CRETACEOUSrrERTIARY BOUNDARY

THOMAS FRITZSCHE, DR. BAHNHOFSTR. 2 37139 ADELEBSEN - GERMANY

KEYWORDS Impact, K-T boundary, catastrophism, mass

ABSTRACT The discovery of anomalies in three Cretaceous-Tertiary sections by the Alvarez team in 1980 prompted them to hypothesize an asteroid impact to explain these unusual concentrations. In the following further evidence provided more support for their hypothesis, but a small minority of scientists are still unconvinced. Since the sciences were confronted with the impact hypothesis heated debates about mass , gradual or extraterrestrial causes, Lyellian uniformitarianism, evolution, and catastrophism got under way. Creationists have taken up this topic reluctantly, perhaps well aware that too much catastrophism may disturb cherished Flood models as well. Nevertheless, impact events did occur and should have their appropriate place in every earth model.

INTRODUCTION Within the last few decades has rediscovered geological catastrophes as powerful means to explain earth history. Extensive volcanism, landslides, tsunamis, turbidity currents and flash floods have been explored, often exceeding our imagination when compared to the processes we observe today. The era of neocatastrophism was in full bloom with the appearance of the famous paper by Alvarez, Alvarez, Asaro and Michel in 1980 [3], hypothesizing an asteroid impact to explain the demise of the , ammonites etc. at the CretaceousfTertiary (K-T) boundary.

Extraterrestrial causes had been suggested earlier. Schindewolf [60] reasoned that there is a nonterrestrial input to mass extinction events. Cosmic radiation, e.g. through a supemova explosion and a higher production of radioactive isotopes, seemed a plausible explanation to him. McLaren in 1970 [42] inferred an asteroid impact to explain the late mass extinction. Urey in 1973 [72] thought cometary impacts in earth history possible and made a rough estimation of the energetic effects. In his view a comet could have killed the dinosaurs and initiated the Tertiary period.

Their speculations were passed over without comment by the scientific community for lack of evidence. Perhaps only the fact that they were well-known scientists protected them from negative reactions. Several explanations for the K-T transition had been suggested but there was no unanimity among the scientists [3]. The incompleteness of the geological record was stressed in former times to overcome the obvious suddenness of extinction the record showed so clearly. But long before the Alvarez paper it was evident that there was no time gap between the Cretaceous and Tertiary.

Though impacts and mass extinctions are accepted by the majority of earth scientists now, extraterrestrial and violent causes were and are still not accepted by some paleontologists, who prefer a causal connection between environmental changes and evolutionary (gradual) processes. So the K­ T impact was an impact for science itself. For the first time since the days of Lyell and scientists had to put their cards on the table and show where they stood: impactor or volcanist, catastrophist or uniformitarian, punctualist or gradualist.

241 The first part of this paper is a short review of the KIT impact issue. In the second part I want to point to some crucial aspects of the matter which affect creationist modeling of earth history. The conclusions are tentative, because much work on the meaning of mass extinctions, sudden events, and the stratigraphie record has to be done.

The Alvarez-paper The story of the iridium anomaly has been repeatedly told [e.g. 4]. In the beginning, it had been the purpose to estimate the sedimentation rates of limestone and a thin clay layer in a K-T section near Gubbio (Italy). Measuring the iridium content of both the limestone and the K-T boundary clay by neutron activation analysis should allow for relative dating. Because iridium and other platinum group elements are depleted in the crust and upper mantle but much more concentrated in chondritic , their abundance in sediments should be a measure for the influx of meteoritic dust onto the earth's surface. The result of their analysis was astonishing. The concentration of iridium in the boundary clay was 30 times above the background concentration. In two other sections, Stevns Klint in Denmark and Woodside Creek in New Zealand, they found concentrations 160 and 20 times above the background values, respectively.

After discussing and excluding other explanations, the authors suggested that a 10 kilometer asteroid might account for the extreme iridium anomalies and the chemical fingerprint of other elements studied. The collision of this bolide with the earth could have launched 60 times the object's mass into the atmosphere. This ejecta layer of dust should stay in the atmosphere for some years, a surmise based on the duration of colored sunsets after the Krakatoa explosion in 1883. In the ensuing discussions this was reduced to some months. The implications for living beings would have been devastating. During the period of darkness photosynthesis was suppressed and gave rise to a breakdown of food chains. As a consequence those bizarre dinosaurs and many other species died out.

K-T boundary research Within the next few years further details of an impact scenario were presented [24, 27, 43, 44, 53, 55, 74]. The immediate event would have been a fireball spreading out from the impact site. The impact would have generated earthquakes measuring up to 13 on the Richter scale [1], about 10000 times more intense than the most violent quakes in our days. A dust cloud would have surrounded the earth and led to darkness. Temperatures would have decreased for some months, but after a short period of cooling global heating due to a terrestrial greenhouse effect would have occurred. Many species are more sensitive to higher temperatures, so this may have been the main killing mechanism. If the impact hit the ocean gigantic waves would have been produced and tsunamis would have flooded all coasts. Turbidity currents would have moved vast amounts of sediments. The shock heating of the atmosphere would have produced nitric oxides and pure nitric acid would have poured down to earth as rain. Depending on the amount of acid the carbonate-buffering capacity of the surface ocean would have been more or less destroyed. The weathering of continental soils could have mobilized trace metals with toxic concentrations. The soot layer at the K-T boundary may even evidence global wildfires ignited through thermal radiation of downfalling ejecta. As for example the production of acid rain depends on the target rocks hidden by the bolide, all calculations of the impact consequences should be taken with some care.

It was initially believed that about 60-75 percent of all existing species at that time died out and no terrestrial weighing more than 25 kilograms survived. Many genera died out or were reduced. The main victims were the dinosaurs (, omithischia, pterosauria), ammonites, belemnites, plesiosaurs, and calcareous microorganisms (foraminifers and coccoliths). Some genera appeared to have experienced complete reduction, like the and snakes, but survived somehow. Many plants, terrestrial mammals, fish and silicaceous planktonic organisms suffered far less.

Some events in the marine realm can produce an iridium anomaly too, and so it was initially hoped that a marine explanation could be found. The anomalies first reported by the Alvarez team were found in chalk sediments attributed to deep sea (Gubbio) or shallow marine environment (Stevns Klint). But a terrestrial site was soon reported by Orth et al. [50] from a drill in the Raton Basin, New Mexico. The iridium anomaly seemed to be evidence of a global event affecting both the oceans and the continents.

242 In the following years the impact got more and more support, the ever growing evidence for an impact convinced one sceptic after another. Sanidine spherules were found in many K-T sections and were interpreted as high temperature indicators [65), representing impact debris falling out from the ejecta cloud. At one point it was hoped that the terrestrial origin of the boundary clay could be demonstrated by the osmium isotope ratios. Terrestrial sources should give ratios of about ten, meteoritic ratios should be about one. Luck and Turekian found ratios of 1.6 for Stevns Klint and 1.29 for Raton Basin, Colorado [40], thus promoting the meteoritic origin .

In 1984 Bohor and his co-workers reported on found in the boundary clay. Quartz with multiple intersecting shock lamellae were known from established craters and nuclear explosion sites [14, 15,62) and had been used to recognize impact structures. From a mineralogical point of view the shocked quartz is perhaps the most significant impact indicator. As Luis Alvarez commented: "I have never seen a sample of shocked quartz, but I did see a sort of shock wave pass through the Earth sciences community when Bohor announced his discovery" [4, p. 29]. The quartz grains also show a spectrum of different colors when submitted to cathodoluminescent light, not observed in grains from volcanic origin [52).

Quartz crystals comprise different modifications depending on their origin. Stishovite is a rare quartz crystal known from some impact sites. The discovery of stishovite in the boundary clay of Raton, New Mexico, again strengthened the impact case [41). In 1989 Zhao & Bada [75) reported on their discovery of extraterrestrial aminoacids in the boundary clay from Stevns Klint. However, the preservation of aminoacids during an is still mysterious. The discovery of microdiamonds in a K-T layer in Alberta was the next indication of impact origin. The geochemical signature makes a chondritic meteorite the likely source [18, 19].

Tektite strewn fields and microtektites seem to be linked to younger impact events, like the Czechoslovakian strewn field to the Ries crater [32). They were interpreted as rapidly molten and quickly cooled terrestrial target rocks. Most of the K-T boundary sections do not contain , but millimeter-sized spherules composed of secondary minerals. These spherules are interpreted as being air-fall deposits from depressured rocks. The worldwide distribution of microspherules in K-T boundary sections also point to an impact origin. Only some microspherules, e.g. those from Haiti, have maintained their glassy structure (13).

Intense volcanism In the mid-eighties a catastrophistic altemative to the impact scenario had developed. Iridium had been detected in the emissions from Kilauea volcano, Hawaii, presumably bounded as iridium fluoride (76). It was not possible to explain the origin of this high concentration in the gases, but a connection of iridium and hot spot volcanism was a promising aspect. In 1989 another iridium emission had been observed [71]. Attention soon focused on the Deccan Traps in India, an intense flood basalt comprising about half a million cubic kilometers today. About 80 percent of the basalts were extruded during the magnetic polarity chron 29R, which includes the K-T transition [26). Eruptions were initiated when the Indian plate passed the Reunion hotspot. Reliable age data spanned from 60 to 67 Ma (11), but new results yielded ages close to the K-T transition. It is difficult to obtain an exact age, because there are some minor deviations e.g. due to argon loss [12). The search for iridium in the Deccan basalts has been negative [59).

The strategy of the so called volcanists was not so much to concentrate on the Deccan Traps, but to strengthen the possibility that intense and perhaps catastrophic volcanism and other terrestrial effects such as sea level fall may explain the observations, too [20, 21, 22). The broadening of the iridium signal, multiple iridium peaks (spikes), iridium abundances together with volcanism, the chemistry of the boundary clay and the microspherules, deformation features in quartz derived from volcanic activity, and a critical review of impact structures were gathered to disprove the postulated impact(s)[33, 47, 48, 49).

The A decade after the Alvarez paper an impact scenario was widely accepted, however, the "smoking gun" was still missing. Since the sixties opinion conceming cryptovolcanic structures had changed,

243 now favouring extraterrestrial (meteoritic) causes for certain phenomena. The Meteor Crater in Arizona and the Ries Crater in Germany were the first to get full approval by scientists as impact structures [29]. The Manson structure in Iowa promised to be the K-T crater, but it is too small. So multiple impacts, perhaps over a period of 1-3 million years were preferred [35]. Many scientists did not expect to find significant craters at all, because those on the ocean floor could have been subducted already.

The Caribbean and Colombian basins were proposed as possible impact sites [16, 34]. Those sites could explain impact related observations like the 50 centimetre-thick layer in Haiti, the boulder bed in Cuba up to 350 metres thick, or the size distribution of shocked quartz. Since 1990 the search has been concentrated on the Gulf of Mexico [7, 54, 66]. The sediment-filled Chicxulub structure is thought to be the killing crater. Melt rocks from drilling cores were similar to the spherules from Haiti and Mexico. Sediments in Mexico and from DSDP drill holes were interpreted as giant wave deposits. The glassy melt rocks in the surmized crater yielded 4OArf39 ages of about 65 Ma [69]. They agreed with the 64.5 Ma for the Haitian tektites obtained by the same method [37] and the 65 Ma for zircons from Haiti, Chicxulub and Colorado. The latter samples had different crystallisation ages but reset u­ Pb ages of about 65 Ma [39].

The Chicxulub crater also solves an embarrassing property of the boundary clay. The chemistry of the impact layer showed signs that the target rocks were both of granitic (continental) and basaltic (oceanic) origin. Multiple impacts on different target rocks therefore seemed conclusive. A single impact on a target of mixed composition could give rise to the different chemical data, and that is exactly what an impact on the Yucatan platform looks like. The supposed crater diameter of 200-300 km [63] leads back to the original proposal by the Alvarez team!

Some further aspects Several papers deal with other extinction events, mostly at the -, Frasnian­ Famennian, - and Triassic- boundaries. Together with the Cretaceous­ Tertiary boundary, these are the five great boundaries. Minor extinction events are postulated for the /, late Cambrian, Oligocene/Eocene, and late Pleistocene [25]. Generally, the typical evidence for meteorite impacts like that at the K-T boundary are missing; only the iridium anomaly at the Oligocene-Eocene boundary and a tektite layer makes this boundary a second candidate.

In the mid-eighties the K-T event had stimulated discussions about periodic extinction events. In a series of papers periodicities between 26 and 31 Ma were postulated [5, 23, 56, 58, 61, 73]. among them a solar companion, called Nemesis, periodically perturbing the 'Oort cloud" and sending comets into the solar system. Since Nemesis has not been found, this hypothesis remains in the background. Obviously, there are impressive correlations between impacts and mass extinctions [5] or flood basalt volcanism and extinction [68]. If plateau basalts are generated by meteorite impacts as proposed by Alt et al. [2], they may be related to some cosmic periodicity. But again, this has not been ultimately proved. The breakup of through impact events and the possible redefinition of tillites and diamictites as impact ejacta depOSits are accompanying hypotheses of the ongoing debates [46, see also 45].

Curiously, the iridium anomalies in the KIT sections that had been the first physical evidence of an asteroid, are not the primary evidence of an impact any more. Iridium anomalies have been found in different stratigraphic sections and even in volcanic dust from Antarctic ice fields [38]. Their incidence may be due to impacts, extensive flood basalt volcanism, accelerated Mid Ocean Ridge basalt generation, and special sedimentary environments. In a painstaking search for iridium and other trace elements, Orth et al. [51] analysed many Phanerozoic bio-event horizons. They found some weak iridium anomalies in other sections, but came to the conclusion that the anomaly at the K-T boundary is still unique. Nevertheless, shocked quartz and high-pressure silicates are now the strongest evidence of meteorite impacts.

Most of the scientists familiar with the K-T debate accept one or more impacts at the boundary, though not everyone agrees upon impacts as the cause of mass extinction. The data strongly imply an impact event at the K-T boundary, though some reservations remain. Extensive volcanism at this time may have contributed to the biotic overtum. Indeed, impact plus volcanism could have been companions causing the mass extinction.

244 The reactions of the scientists to the Alvarez paper ranged from enthusiastic to critical. Those scientists involved in astronomy and astrophysics had no problems with the Alvarez proposal. Comets and asteroids, impacts and impact craters, were in harmony with their own research. For many micropaleontologists the asteroid story sounded conclusive, too, because they were well aware of the sudden disappearance of microorganisms. But many geologists and paleontologists were skeptical and remained so in the following years. For macropaleontologists, who had spent a lot of time developing sophisticated ideas based on evolution to explain the demise of so many species, the impact scenario seemed to destroy their lifework.

Indeed, the extinction and survival record across the K-T boundary is ambiguous. The impact scenario cannot explain all the details of selection, because its violence and the bulk of perilous consequences would have selected its victims arbitrarily. Several terrestrial explanations had been offered and were discussed anew. Climatic changes, a world-wide marine regression or a fresh water flood from the Arctic were among the possible earth-bound explanations, not to mention all the speculations about the dying of the dinosaurs, which attracted nearly all the public interest

Some confusion about the K-T event(s) seem to originate in diverging sampling procedures, different sites studied, the handling of the data, and the efficacy of causes hypothesized to lead to extinctions. For example, the global dust cloud after the impact made it easy to visualize the dying of the dinosaurs. Yet, in 1987 Brouwers et al. (17) reported on fossils at high paleolatitudes. If dinosaurs were well adapted to periods of darkness and winter seasons, how could the dust cloud cause their demise? To take another example, Archibald and Bryant (8) had analysed the survivorship of the terrestrial fauna from the Cretaceous to the Tertiary. Correcting for rare species, among other things, their results indicated a survivorship of 53 percent. When divided into freshwater and land­ dwelling vertebrates, however, the survivorship is 90 percent in the freshwater assemblage and only 12 percent in the land-dwelling assemblage (64). Contrary to the assertion that no important extinction occurred, land-dwelling vertrebrates suffered severely from the K-T event. To be realistic, there will always be some uncertainties when examining the biological and geological remains, so debates will continue for ever.

THE KTB AND CREATIONISM As far as I know, the only creationist paper conceming the K-T boundary is from Froede and DeYoung (31). Other authors do refer to the K-T event, but concentrate on different topics. While I am at variance with Froede and Young's conclusion that a meteorite (asteroid) bombardment occurred at the beginning of the Flood, they did outline the importance of the impact issue. Interestingly, the whole issue found only small reference in creationist literature.

The impact/mass extinction issue is crucial for creationists for two reasons. First, impacts and all their possible consequences are puzzling within gradualistic concepts, such as Darwinian evolutionary theory and Lyellian uniformitarianism. There is no other topic in earth sciences which offers so much criticism of gradualistic concepts and favours catastrophism as the impact discussion, see e.g. Alvarez et aI., HsO, and Raup [6, 36, 57).

Secondly, impacts pose challenges to a young-earth view. This is of course not valid for the impact scenario itself. An impact is a natural (actualistic) cause to explain the cataclysmic rainfall at the beginning of the Flood. Gigantic waves, tsunamis, intense earthquakes and volcanism, all together build up an impressive Flood scenario. It has become obvious from the impact discussion that the biblical Flood may be explained in terms of the ongoing impact debate.

In 1993 a book by two well-known Austrian geologists, Alexander and Edith Tollmann (70), appeared. Stimulated by the impact debates, they had examined traditions and flood histories from all over the world. They concluded that a series of cometary impacts struck the earth about 9545 years ago. This date is based upon radiocarbon and tree-ring chronology. Of course, they accept the geologic time­ frame and it should be stated that their comments about the biblical Flood are unfriendly. Some of their conclusions are rather fanciful. Among other things, they interpret dragon illustrations as a symbol of cometary impacts. The most valuable aspect of the book was to recall the geological contents of historical documents, often overlooked and presumably not allowed for by many geologists, archeologists, anthropologists, ethnographers and theologians. It was a rare opportunity for many people in Central-Europe to be reminded of these reflections.

245 Presently, there are other problems for a young-earth view, however, which are more interesting. Flood geology is still a developing issue and a closer look at the geological data has led to different Flood models within the last few years. It has become an urgent wish to produce a common and representative overview of what creationists should really be looking for. The K-T boundary is one topic in earth sciences that creationists will have to acquaint themselves with, because many contributions from different areas of research are available and allow critical evaluations of the efficiency of Flood models. I want to address five areas: a. Stratigraphy Looking back over the last few decades of creationist research one notes that it has been common to cast doubts on the stratigraphical record. Of late, some creationists have taken a different position [10] irrespective of the postulated evolution and hundreds of millions of years. On the whole, the system built up by scientists in the first part of the nineteenth century still works well.

What really has to be explained are the stratigraphic positions of sudden disappearances of certain groups and the sudden appearance of others. On a fine or local scale - measuring decimetres to a few metres - corrections are still to be expected on the basis of future research. Corrections on a larger scale would be exceptions and would surely not disturb the whole system. The way scientists searched for K-T sections to check the Alvarez-proposal is fine evidence, they had only to look at the geological maps and descriptions. 50 the K-T boundary with all its implications is a fine illustration of what stratigraphy is good for, how it ' works" when scientists are challenged to test for a global event.

It is well known from catastrophic events like the Mount 5t. Helens eruptions that thin layering in pyroclastic flow deposits was the result of turbulent flows. The stratification of sediments formed in water may also be the result of fast-flowing suspensions. But if there were several meteorite impacts within the Flood there would have been some sort of chaotic sedimentation and erosion not allowing for a regular pattem in the embedment of living and dead animals. To put it simply: if trilobites, dinosaurs, mammals and men lived at the same time, they would be found together at least in some places in the fossil record. All who are familiar with geology know that no such site has been found to date. b. Sedimentation rate for impact debris and erosion The boundary clay is on average 2-8 mm thick in marine sediments and 2-3 centimeters thick in terrestrial sediments. From a uniformitarian point of view, a boundary only a few centimeters thick can still represent a period of thousands or even ten thousands of years. if one is strict, this extraordinary fine scale does not allow one to take an impact event as the real cause of a mass extinction, because its effects are still too short to be identified on such a scale. Slow sedimentation rates in deep marine environments on the one hand and the incompleteness of the geological record on the other, may always be an argument against mass extinction events as such.

Flood geology aims at high sedimentation rates instead. The crucial point is: Can the Flood allow for a distinctive and thin layer of impact debris? Flood models try to explain strata many kilometers thick formed during the Flood. The K-T layer is only a few centimetres thick. If we think 'uniformitarianly", this implies a very short time, only some hours in comparison to the one-year Flood. We have to take into account the formation of a global dust cloud (weeks), its falling (months), and the sink velocity of the particles (years?). It is possible to produce the sedimentary features in 1-3 years, but this is much too long for the Flood year!

The clay marks a boundary, a global event with a characteristic signature. There are fossils of ammonites, belemnites, certain microfossils, and dinosaurs right up to the boundary. There is still much debate about the last appearance of certain groups of fossils. Some palaeontologists maintain that the oldest reliable dinosaur fossils were found two or three meters below the boundary. On the other hand, dinosaur fossils were found in the Tertiary, but the stratigraphic position of the K-T boundary in these sites is disputed. Some reworked or redistributed fossils do exist [9]. On a more rough scale (a few metres), there is a clear break in the fossil record. Fast sedimentation and extensive erosion shortly after the Flood would be expected to redistribute many Cretaceous fossils and disturb the boundary signature. The process of reworking would be a voluminous one. Both, the

246 regularity in the fossil record and the preservation of a thin event layer, are a challenge to Flood models.

c. How many "events" are there in the geological record? Froede pointed out that the global iridium-anomaly marks an event, not necessarily a time [30]. If the iridium-anomaly is an event, however, there are other events too, like the great unconformity at the Precambrian/Cambrian boundary, which for many creationists marks the onset of the Flood. Earth scientists have identified five great mass extinctions and a couple of minor ones. Are these extinctions "events"? Within the last few decades event stratigraphy has become a prominent field of research, and many local and global "events" have been postulated. How does this fit into a Flood model?

Creationists often concentrate on two events, the beginning and the end of the Flood. Incidentally, where to place the end of the Flood in the geological record (in so far as the record is accepted at all), was a crucial topic in the CEN TechJoumal in 1996 [67]. However, the onset and the end of the Flood may appear as gradual in the geological record and may possibly not be linked to the events so far postulated by geologists. It will probably be impossible to find these two significant pOints in the geological record. Further conflict arises from a dozen or more "events" which have to be carefully analysed and explained by Flood geologists. Problematic as the evidence seems to be for a one-year Flood, there is also an opportunity for Flood geology. If some of the events could be explained by Flood conditions, this may help to restrict the Flood strata. d. Impact craters There is not only the K-T impact and its supposed crater on the Yucatan peninsula. To date more than 150 impact craters have been identified, ranging from little structures like the Arizona crater, via medium-sized ones like the Nordlinger Ries in Germany, to Popigai in Siberia or the Sudbury and Vredefort structures. They seem to be regularly distributed in the geological column [5]. The absence of even bigger craters, though expected from the size distribution and the notion that there were even more objects in former times, is explained by erosion, sedimentation, subduction and some tumover events in the first few hundred million years of the earth. Craters on the moon and in the solar system are a crude estimate what has happened to the earth. This is valid if the earth and its satellite had a common history, as is inferred from the Bible. The craters on the moon surface are therefore a measure for the impacts on earth.

However, it is difficult to imagine how on earth could survive such a bombardment. The most serious consequences are intiated by meteorites falling into the ocean. The chemical consequences of one bolide colliding with the earth depend among other factors on the size of the bolide and the place hit. But dozens of meteorites within the Flood year would seem to have been an overkill for the whole earth and the ark too. It must be bome in mind that the impact scenario is not what the Bible tells us about the Flood. Ironically, the craters confront creationists with too much catastrophism! e. Flood models Though it is not my intention in this paper to favour one model or the other, some critical evaluation is necessary. The sudden disappearance of many species at the boundaries labeled as mass extinction events does not seem to fit into a Phanerozoic Flood model, if the Jurassic, Cretaceous and part of the Tertiary were laid down during the Flood. The problem of mass extinction events, especially at the K-T boundary with its unique appearance, is not easy to explain even in the Paleozoic Flood model. This model allows for a little time and has the task of explaining much of the Mesozoic and Cenozoic strata within a short time-frame, thereby allowing mankind to disembark from the ark and to colonize the earth again. Mankind had survived post-Flood impacts then, like that at the K-T transition.

The K-T boundary may perhaps mark the end-Flood situation. If the impact occurred almost at the end of the Flood, a short period of calm after the Flood event would allow the impact debris to settle down. But after that short interval the deposition of the Cenozoic strata would have begun, also as catastrophic events. The Cenozoic impacts may now give an additional impulse for geological processes. This scenario is mere speculation, but it may explain the extraordinary preservation of the K-T boundary. Of course, this is an unsatisfactory proposal with regard to the boundary sections being interpreted as terrestrial. I do not think that the existing Flood models are sophisticated enough to answer the boundary question(s) properly.

247 CONCLUSION Indeed, a more gradual transition like that proposed by the volcanists and still maintained by many paleontologists (evolutionists) would be favourable to creationists, because a distinct impact layer represents too much time when compared to all strata to be explained in the Flood year. In some way the critical points emphasized by the volcanists fit well in a young earth view. The spreading of the iridium anomaly, multiple iridium peaks, or the discrepancy between the iridium and fossil "boundary signal" at some sites, e.g. DSDP site 524 and 465 [47), can be interpreted in terms of higher sedimentation rates at that time.

On the other hand, the evidence for an impact is overwhelming. In a short time-frame, as implied by every Flood model, the impact and flood basalt volcanism occurred almost simultaneously. So both competing hypotheses may be combined. If there is a correlation between impacts and flood basalt volcanism, the bolides may produce earthquakes or tectonic disturbances by which intense Flood generated magma reservoirs are tapped. Impacts breaking up continents may accelerate geological processes to a certain degree is yet another hypothesis to be considered [28, 46).

Intensively studied issues like the K-T boundary are great resources for any Flood model. It should be emphasized that the discussion among scientists favouring different models and causes provides an impressive database. Because scientists defending a certain position try everything to disprove the hypothesis of their colleagues, there is reason to believe that nearly all arguments have been advanced. If one has a quite different understanding of earth history, like the young-earth view or Flood geology, this situation is welcome. It helps to see both sides of the coin and give reasonable credit to both hypotheses. An altemative can be based on nearly all accessible data, a situation often blurred in science because of the dominance of one paradigm.

Of course, the controversy about mass extinctions and the importance of catastrophic events in earth history corresponds quite well to the considerations of young-earth proponents, who see the biblical Flood as the centre of geological modeling. In the century after Lyell it was usual to mock catastrophists. Today there is no reason to be proud of that, because evident geological features were misinterpreted while the world was seen through the eyes of gradualism.

Nevertheless, impact events pose some problems for creationists too. Creationists have to explain how survival during impacts is possible on a short time-scale at all. Since every earth-history has to incorporate meteorite impacts (or to explain why there were no giant impacts, contrary to astronomical theory) a more profound understanding is necessary. Perhaps, impacts and their consequences are the master-key to an understanding of what really happened in the past and especially within a Biblical time frame. Further research is urgently needed.

REFERENCES [1) Ahrens, T.J. and O'Keefe, J.D., Impact of an asteroid or comet In the ocean and extinction of terrestrial life, Joumal of Geophysical Research. Supplement, 88(1983), pp. A799-A806. [2) AIt, D., Sears, J.M. and Hyndman, D,W., Terrestrial marla: The origins of large basalt plateaus, hotspot tracks and spreading ridges, The Joumal of Geology, 96(1988), pp. 647- 662. (3) Alvarez, L.W., Alvarez, W., Asaro, F. and Michel, H.V., Extraterrestrial cause for the Cretaceous-Tertiary extinction, Science, 208(1980), pp. 1095-1108. (4) Alvarez, L.W., Mass extinctions caused by large bolide Impacts, Physics Today, 40:7 (1987), pp. 24-33. [5) Alvarez, W. and Muller, A.A., Evidence from crater ages for periodic impacts on the Earth, Nature, 308(1984), pp. 718-720. (6) Alvarez, W., Hansen, T., Hut, P., Kauffman, E.G. and Shoemaker, E.M., Uniformitarianism and the response of earth scientists to the theory of Impact crises, In: Catastrophes and evolution: astronomical foundations, S.V.M. Clube, Editor, 1989, Cambridge University Press, pp. 13-24. (7) Alvarez, W., Smit, J., Lowrie, W., Asaro, F., Margolis, S.V., Claeys, P., Kastner, M. and Hildebrand, A.A., Proximal impact deposits at the Cretaceous-Tertiary boundary In the

248 Gulf of Mexico: A restudy of DSDP Leg 77 Sites 536 and 540, Geology, 20(1992), pp. 697- 700. [8] Archibald, J.D. and Bryant, L.J., Differential CretaceouslTertlary extinctions of nonmarine vertebrates: Evidence from northeastern Montana, In: Global catastrophes in earth history: An interdisciplinary conference on impacts, volcanism, and mass mortality, V.L. Sharpton and P.D. Ward, Editors, Geological SOCiety of America Special Paper 247, 1990, pp. 549-562. [9] Archibald, J.D., Dinosaur Extinction and the End of an Era: What the Fossils Say, 1996, Columbia University Press, New York. [10] Snelling, A.A., Ernst, M., Scheven, E., Scheven, J., Austin, S.A., Wise, K.P., Gamer, P., Garton, M. and Tyler, D., The Geological Record (Statement), Creation Ex Nihilo Technical Joumal, 10(1996), pp. 333-334. [11] Baksi, A.K., Critical evaluation of the age of the Deccan Traps, India: Implications for flood-basalt volcanism and faunal extinctions, Geology, 15(1987), pp. 147-150. [12] Baksi, A.K., Geochronological studies on whole-rock basalts, Deccan Traps, India: evaluation of the timing of volcanism relative to the K-T boundary, Earth and Planetarv Science Letters, 121 (1994), pp. 43-56. [13] Blum, J.D. and Chamberlain, C.P., Oxygen Isotope constraints on the origin of impact glasses from the Cretaceous-Tertiary boundary, Science, 257(1992), pp. 1104-1107. [14] Bohor, B.F. , Foord, E.E., Modreski, P.J. and Triplehom, D.M., Mineralogic evidence for an impact event at the Cretaceous-Tertiary boundary, Science, 224(1984), pp. 867-869. [15] Bohor, B.F., Modreski, P.J. and Foord, E.E., Shocked quartz In the CretaceOUS-Tertiary boundary clays: evidence for a global distribution, Science, 236(1987), pp. 705-709. [16] Bohor, B.F. and Seitz, R., Cuban KIT catastrophe, Nature, 344(1990), 593. [17] Brouwers, E.M., Clemens, W.A., Spicer, R.A., Ager, T.A., Carter, L.D. and Sliter, W.V., Dinosaurs on the North Slope, Alaska: High latitude, latest Cretaceous environments, Science, 237(1987), pp. 1608-1610. [18] Carlisle, D.B. and Braman, D.R., Nanometre-slze diamonds In the CretaceouslTertiary boundary clay of Alberta, Nature, 352(1991), pp. 708-709. [19] Carlisle, D.B., Diamonds at the KIT boundary, Nature, 357(1992), pp. 119-120. [20] Carter, N.L., Officer, C.B., Chesner, C.A. and Rose, W.I., Dynamic deformation of volcanic ejecta from the Toba caldera: Possible relevance to CretaceouslTertlary boundary phenomena, Geology. 14(1986), pp. 380-383. [21] Courtillot, V.E. and Cisowski, S., The Cretaceous-Tertiary boundary events: External or Internal causes?, EOS. Transactions of the American Geophysical Union, 68(1987), pp. 193- 200. [22] Crocket, J.H., Officer, C.B., Wezel, F.C. and Johnson, G.D., Distribution of noble metals across the CretaceouslTertlary boundary at Gubbio, Italy: Iridium variation as a constraint on the duration and nature of CretaceouslTertiary boundary events, Geology, 16(1988), pp. 77-80. [23] Davis, M., Hut, P. and Muller, R.A., Extinction of species by periodic comet showers, Nature, 308(1984), pp. 715-717. [24] D'Hondt, S., Pilson, M.E., Sigurdsson, H., Hanson, A.K. and Carey S., Surface-water acidification and extinction at the CretaceOUS-Tertiary boundary, Geology, 22(1994), pp. 983-986. [25] Donovan, S.K., Editor, Mass extinctions: Processes and evidence. Introduction, 1990, Enke, Stuttgart, pp. XI-XIV. [26] Duncan, R.A. and Pyle, D.G., Rapid eruption of the Deccan flood basalts at the CretaceouslTertiary boundary, Nature, 333(1988), pp. 841-843. [27] Emiliani, C., Kraus, E.B. and Shoemaker, E.M., Sudden death at the end of the Mesozoic, Earth and Planetary Science Letters, 55(1981), pp. 317-334. [28] Fischer, J.M., A giant meteorite impact and rapid continental drift, Proceedings of the Third Intemational Conference on Creationism, R.E. Walsh, Editor, 1994, Creation Science Fellowship, Inc., Pittsburgh, PA, Volume 1, pp. 185-197. [29] French, B.M., 25 years of the impact-volcanic controversy, EOS, Transactions of the American Geophysical Union, 71 (1990), pp. 411-414. [30] Froede, C.R., Iridium in the geological column, Creation Research Society Quarterly, 31 (1994), pp. 135-136. [31] Froede, C.R. and DeYoung, D.B., Impact events within the young-earth flood model, Creation Research Society Quarterly. 33(1996), pp. 23-34.

249 [32] Glass, B.P., Tektites and mlcrotektltes: key facts and Inferences, Tectonophysics, 171 (1990), pp. 393-404. [33) Hallam, A., End-Cretaceous mass : Argument for terrestrial causation, Science, 238(1987), pp. 1237-1242. [34) Hildebrand, A.R. and Boynton, W.V., Proximal Cretaceous-Tertiary boundary impact deposits in the Caribbean, Science, 248(1990), pp. 843-847. [35] Hut, P., Alvarez, W., Elder, W.P., Hansen, T., Kauffman, E.G., Keller, G., Shoemaker, E.M. and Weissman, P.R., Comet showers as a cause of mass extinctions, Nature, 329(1987), pp.118-126. [36] HsO, K.J., The Great Dying, 1986, Harcourt Brace Jovanovich, New York. [37) Izett, G.A., Dalrymple, G.B. and Snee, L.W., 4OArr9Ar age of Cretaceous-Tertiary boundary tektites from Haiti, Science, 252(1991), pp. 1539-1542. [38] KoeberJ, C., Iridium enrichment in volcanic dust from blue ice fields, Antarctica, and possible relevance to the KIT boundary event, Earth and Planetary Science Letters, 92(1989), pp. 317-322. [39] Krogh, T.E. , Kamo, S.L., Sharpton, V.L., Marin, L.E. and Hildebrand, A.A., U-Pb ages of single shocked zircons linking distal KIT ejecta to the Chicxulub crater, Nature, 366(1993), pp. 731-734. [40] Luck, J.M. and Turekian, K.K., Osmium-187/0smium-186 In manganese nodules and the Cretaceous-Tertiary boundary, Science, 222(1983), pp. 613-615. [41] McHone, J.F., Neiman, A.A., Lewis, C.F. and Yates A.M., Stlshovlte at the Cretaceous­ Tertiary boundary, Raton, New Mexico, Science, 243(1989), pp. 1182-1184. [42] McLaren, D.J., Time, life and boundaries, Journal of Paleontology. 44(1970), pp. 801-815. [43] McLaren, D.J. and Goodfellow, W.O., Geological and biological consequences of giant impacts, Annual Reviews of Earth and Planetary Sciences, 18(1990), pp. 123-171. (44) Melosh, H.J., Schneider, N.M., Zahnle, K.J. and Latham, D., Ignition of global wildfires at the CretaceouslTertiary boundary, Nature, 251 (1990), pp. 251-254. [45] Molen, M., Diamictites: Ice-ages or gravity flows?, Proceedings of the Third International Conference on Creationism, A.E. Walsh, Editor, 1994, Creation Science Fellowship, Inc., Pittsburgh, PA, pp. 353-367. [46] Oberbeck, V.A., Marshall, J.A. and Aggarwal, H., Impacts, tillites, and the breakup of Gondwanaland, The Journal of Geology, 101(1993), pp. 1-19. [47] Officer, C.B. and Drake, C.L., The Cretaceous-Tertiary transition, Science, 219(1983), pp. 1383-1390. (48) Officer, C.B. and Drake, C.L., CretaceouslTertiary extinctions. We know the answer, but what is the question?, EOS. Transactions of the American Geophysical Union, 70(1989), pp. 659-661. [49] Officer, C.B., The relevance of Iridium and microscopic dynamic deformation features toward understanding the CretaceouslTertlary transition, Terra Nova, 4(1992), pp. 394- 404. [50] Orth, C.J., Gilmore, J.S., Knight, J.D., Pillmore, C.L., Tschudy, A.H. and Fassett, J.E., An Iridium abundance anomaly at the palynological Cretaceous-Tertiary boundary in northern New Mexico, Science, 214(1981), pp. 1341-1343. [51] Orth, C.J., Attrep Jr., M. and Quintana, L.A., Iridium abundance patterns across bio-event horizons In the fossil record, In: Global catastrophes in earth history: An interdisciplinary conference on impacts volcanism, and mass mortality, V.L. Sharpton and P.J. Ward, Editors, Geological Society of America Special Paper 247, (1990), pp. 45-59. [52] Owen, M.A. and Anders, M.H., Evidence from cathodoluminescence for non-volcanic origin of shocked quartz at the CretaceouslTertlary boundary, Nature, 334(1988), pp. 145- 146. [53] Pollack, J.B., Toon, O.B., Ackerman, T.P. and McKay, C.P., Environmental effects of an impact-generated dust cloud: implications for the Cretaceous-Tertiary extinctions, Science, 219(1983), pp. 287-289. [54] Pope, K.O., Ocampo, A.C. and Duller, C.E., Mexican site for KIT , Nature, 351 (1991), 105. [55] Prinn, A.G. and Fegley B., Bolide Impacts, acid rain, and blosperlc traumas at the Cretaceous-Tertiary boundary, Earth and Planetary Science Letters, 83(1987), pp. 1-15. [56] Rampino, M.A. and Stothers, A.B., Terrestrial mass extinctions, cometary impacts and the 's motion perpendicular to the galactic plane, Nature, 308(1984), pp. 709-712. [57] Raup, D.M., The Nemesis Affair, 1986, Norton, New York, London.

250 [58] Raup, D.M. and Sepkoski, J.J., Periodic extinction of families and genera, Science, 231(1986), pp. 833-836. [59) Rocchia, A. , Boclet, D., Courtillot, V. and Jaeger, J.J, A search for iridium in the Deccan Traps and inter-traps, Geophysical Research Letters, 15(1988), pp. 812-815. (60) Schindewolf, O.H., Ober die moglichen Ursachen der groBen erdgeschichtlichen Faunenschnitte, Neues Jahrbuch fOr Geologie und Palaontologie. Monatshefte, 1954, pp. 457-465. [61] Schwartz, A.D. and James, P.B., Periodic mass extinctions and the Sun's oscillation about the galactic plane, Nature, 308 (1984), pp. 712-713. [62] Seitz, A. and Bohor, B.F., Shocked quartz grains at the Cretaceous-Tertiary boundary, Naturwissenschaften, 75(1988), pp. 307-308. (63) Sharpton, V.L., Exploring the KT source crater: Progress and future prospects, EOS. Transactions of the American Geophysical Union, 76(1995), 534-538. (64) Sheehan, P.M. and Fastovsky, D.E., Major extinctions of land-dwelling vertebrates at the Cretaceous-Tertiary boundary, eastern Montana, Geology, 20 (1992), pp. 556-560. [65] Smit, J. and Klaver, G., Sanidlne spherules at the Cretaceous-Tertiary boundary indicate a large Impact event, Nature, 292(1981), pp. 47-49. [66] Smit, J., Montanari, A., Swinbume, N.H.M., Alvarez, W., Hildebrand, A.A., Margolis, S.V., Claeys, P., Lowrie, W. and Asaro F. , Tektite-bearing, deep-water clastic unit at the Cretaceous-Tertiary boundary In northeastern Mexico, Geology. 20(1992), pp. 99-103. (67) Snelling, A.A., Where should we place the Flood/post-Flood boundary In the geological record?, Creation Ex Nihilo Technical Joumal, 10(1996), pp. 29-31. (68) Stothers, A.B., Flood basalts and extinction events, Geophysical Research Letters, 20(1993), pp. 1399-1402. [69] Swisher, C.C., Grajales-Nishimura, J.M., Montanari, A., Margolis, S.V., Claeys, P., Alvarez, W., Renne, P., Cedillo-Pardo, E., Maurrasse, F. J.-M. A., Curtis, G.H., Smit, J. and McWilliams, M.O., Coeval 40Arr9Ar ages of 65.0 million years ago from Chicxulub crater melt rock and Cretaceous-Tertiary boundary tektites, Science, 257(1992), pp. 954-958. (70) Tollman, A. and Tollmann, E., Und die Sintflut gab es doch, 1993, Droemer Knaur, MOnchen . (71) Toutain, J.-P. and Meyer, G., Iridium-bearing sublimates at a hot-spot volcano (Piton de la Fournalse, Indian Ocean), Geophysical Research Letters, 16(1989), pp. 1391-1394. [72] Urey, H.C., Cometary collisions and geological periods, Nature, 242(1973), pp. 32-33. [73] Whitmire, D.P. and Jackson, A.A. , Are periodic mass extinctions driven by a distant solar companion?, Nature, 308(1984), pp. 713-715. [74] Wolbach, W.S., Gilmour, I., Anders, E., Orth, C.J. and Brooks, A.A., Global fire at the Cretaceous-Tertiary boundary, Nature, 334(1988), pp. 665-669. [75] Zhao, M. and Bada, J.L., Extraterrestrial amino acids in CretaceouslTertiary boundary sediments at Stevns Klint, Denmark, Nature, 339(1989), pp. 463-465. [76] Zoller, W.H., Parrington, J.A. and Phelan Kotra J.M., Iridium enrichment in airborne particles from Kilauea Volcano: January 1983, Science, 222(1983), pp. 1118-1121 .

251 252