Hostname: page-component-5cf477f64f-mgq6s Total loading time: 0 Render date: 2025-04-07T16:01:39.400Z Has data issue: false hasContentIssue false
  • English
  • Français

Catastrophes, expectations, and the evidence - Geological Implications of Impacts of Large Asteroids and Comets on the Earth.L. T. Silver and P. H. Schultz (eds.). Geological Society of America, Special Paper 190. 1982. xix + 528 pp. $40.00 (paper).

Published online by Cambridge University Press:  08 April 2016

Leigh M. Van Valen
Leigh M. Van Valen*
Affiliation:
Biology Department (Whitman), University of Chicago, 915 East 57th Street, Chicago, Ill. 60637
Get access Rights & Permissions [Opens in a new window]

Abstract

An abstract is not available for this content so a preview has been provided. Please use the Get access link above for information on how to access this content.
Image of the first page of this content. For PDF version, please use the ‘Save PDF’ preceeding this image.'
Type
Reviews
Information
Paleobiology , Volume 10 , Issue 1 , Winter 1984 , pp. 121 - 137
Copyright
Copyright © The Paleontological Society 

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

References and Notes

1.Shoemaker, E. M. 1983. Asteroid and comet bombardment of the Earth. Ann. Rev. Earth Planet. Sci. 11:461–494.CrossRefGoogle Scholar
2.Halliday, I. 1982. Looking back on the Tunguska event. Syllogeus. 39:138–139.Google Scholar
3.Ganapathy, R. 1983. The Tunguska explosion of 1908: discovery of meteoritic debris near the explosion site and at the South Pole. Science. 220:1158–1161.Google Scholar
4.I do not accept the Tertiary as a geochronologic or stratigraphic unit. To do so implies that the “Quaternary” is of equivalent rank, a proposition for which I know of no support beyond the inertia of tradition. Such tradition has earlier been broken with respect to the “Primary” and “Secondary.” The Cenozoic can usefully be divided into the Paleogene and Neogene periods, apparently a slowly growing practice.Google Scholar
5.Van Valen, L. M. and Sloan, R. E. 1977. Contemporaneity of late Cretaceous extinctions. Nature. 270:193.Google Scholar
6.Alvarez, L. 1983. Experimental evidence that an asteroid impact led to the extinction of many species 65 Myr ago. Proc. Natl. Acad. Sci. U.S.A. 80:627–642. “… a physicist can react instantaneously when you give him some evidence that destroys a theory that he previously had believed. But that is not true in all branches of science, as I am finding out” (p. 629). “I really cannot conceal my amazement that some paleontologists prefer to think that dinosaurs, which had survived all sorts of severe environmental changes and flourished for 140 million years, would suddenly, and for no specified reason, disappear from the face of the earth (to say nothing of the giant reptiles in the oceans and air) in a period measured in tens of thousands of years” (p. 639). Thus he seems to have no respect for the real contrary evidence, which he has seen.Google Scholar
7.Romein, A.J. T. 1982. The Cretaceous/Tertiary boundary: an astronomic or a sedimentary problem? Pp. 123–127. Abst. Int. Assoc. Sedimentol. 3d European Meeting.Google Scholar
8.Clube and Napier (9) suggest that the impact was from an asteroid of a class derived from comets (cf. also Wetherill and Shoemaker, GII). Like others, they exclude a direct cometary impact because the latter should be much rarer (although this has also been disputed—see [10] below) and because the expected frequency of major asteroid impacts resembles that of major extinctions. This of course assumes that most or all major extinctions were caused by impacts, and in addition it is empirically false on available data, as I discuss below.Google Scholar
9.Clube, S. V. M. and Napier, W. M. 1983. Extinction by comet or asteroid? Nature. 303:10.CrossRefGoogle Scholar
10.Shoemaker, and Wolfe, , quoted byEmiliani, C., Krause, E. B., and Shoemaker, E. M. 1981. Sudden death at the end of the Mesozoic. Earth Planet. Sci. Let. 55:317–334. See alsoWeissman, (GII).Google Scholar
11.Alvarez, L. W., Alvarez, W., Asaro, F., and Michel, H. V. 1980. Extraterrestrial cause for the Cretaceous-Tertiary extinction. Science. 208:1095–1108. They had tentatively proposed an unspecified extraterrestrial “solar-system source” in September 1979 (see [13]) and distributed a longer version [14] of their Science paper in December. An earlier abstract [15] (for a meeting in May and June, but published in October) reported an iridium anomaly but suggested only the supernova hypothesis. Meanwhile Napier and Clube [16] published their impact hypothesis in November in a paper “received 7 June,” and a few months later (9 days before the long paper by Alvarez et al. appeared) came two other papers supporting an impact. One, by Hsü [17], I had seen in manuscript in 1979; the other, by Smit and Hertogen [18], reported the authors' own measuremenets of trace-element enrichment at a different locality but referred to one of the Alvarez abstracts; Smit had, however, earlier published [19] a report of trace-element enrichment which they had not yet interpreted. Thus, even apart from earlier speculations with no evidence, the origin of the impact hypothesis seems somewhat diffuse.Google Scholar
12.The supernova hypothesis has nevertheless just been revived. SeeYayanos, A. A. 1983. Thermal neutrons could be a cause of biological extinctions 65 Myr ago. Nature. 303:797–800. It relies on an incorrect pattern of extinction (see below) and seems to have nothing in its favor, nor does it adequately rebut the contrary evidence.Google Scholar
13.Alvarez, W., Alvarez, L. W., Asaro, F., and Michel, H. V. 1979. Anomalous iridium levels at the Cretaceous-Tertiary boundary at Gubbio, Italy: negative results of a test for supernova origin. Geol. Soc. Am. Abst. Prog. 27:378. Also in: Christensen, W. K. and Birkelund, T., eds. Proc. Cretaceous/Tertiary Boundary Events Symp. 2:69. Univ. Copenhagen.Google Scholar
14.Alvarez, L. W., Alvarez, W., Asaro, F., and Michel, H. V. 1979. Extraterrestrial cause for the Cretaceous-Tertiary extinction: experiment and theory. 86 pp. Lawrence Berkeley Lab., Report LBL-9666.Google Scholar
15.Alvarez, W., Alvarez, L. W., Asaro, F., and Michel, H. V. 1979. Experimental evidence in support of an extra-terrestrial trigger for the Cretaceous-Tertiary extinctions. Eos. 60:734.Google Scholar
16.Napier, W. M., and Clube, S. V. M. 1979. A theory of terrestrial catastrophism. Nature. 282:455–459.CrossRefGoogle Scholar
17.Hsü, K. J. 1980. Terrestrial catastrophe caused by a cometary impact at the end of Cretaceous. Nature. 285:201–203.Google Scholar
18.Smit, J. and Hertogen, J. 1980. An extraterrestrial event at the Cretaceous-Tertiary boundary. Nature. 285:198–200.Google Scholar
19.Smit, J. 1979. The Cretaceous/Tertiary transition in the Barranco del Gredero, Spain. In: Christensen, W. K. and Birkelund, T., eds. Proc. Cretaceous/Tertiary Boundary Events Symp. 2:156–163. Univ. Copenhagen.Google Scholar
20.O'Keefe, J. A.Lecture at Univ. Chicago, 1982.Google Scholar
21.The explosion of Krakatau in 1883 increased haze worldwide, but this was from aerosols rather than dust (Toon, et al., GII).Google Scholar
22.The depletion of the Pt group thus provides an indirect argument against the hypothesis of the mantle-core boundary being a phase change. This hypothesis is still advocated:Lyttleton, R. A. 1982. The Earth and Its Mountains. 206 pp. Wiley; New York.Google Scholar
23.Kent, D. V. 1981. Asteroid extinction hypothesis. Science. 211:648–650. The background concentration of Ir in Pleistocene marine sediments from the far-south Pacific in fact reaches a level as high as the K-Pg peak at Gubbio, Italy.CrossRefGoogle ScholarPubMed
24.There are several dozen sites where high Ir concentrations have been found at the K-Pg boundary; similar clays elsewhere in some of the same sections are normal. A shallow carbonate-compensation depth at the boundary, for which there is other evidence (Hsü et al. [GII] and much earlier work by others), would account for this pattern qualitatively but not quantitatively. Moreover, the rare-earth elements are variably depleted at the boundary [25]. Smit [26, p. 39] notes that dinoflagellates have about the same normal species turnover as coccolithophores but only the latter have their ranges truncated at the boundary; a hiatus long enough to concentrate Ir adequately should affect both groups appreciably and also affect the magnetostratigraphy. And dissolution of limestone is irrelevant to the Ir peaks in terrestrial sediments.Google Scholar
25.Smit, J. and ten Kate, W. G. H. Z. 1982. Trace-element patterns at the Cretaceous-Tertiary boundary—consequences of a large impact. Cretaceous Res. 3:307–332.Google Scholar
26.Russell, D. A. and Rice, G. (eds.) 1982. K-Tec II: Cretaceous-Tertiary extinctions and possible terrestrial and extraterrestrial causes. Syllogeus. 39:1–151.Google Scholar
27.Thierstein (GII) makes two partly offsetting arithmetical errors in the first two steps of his calculation, one being off by two orders of magnitude, and misstates mg as ml. My repetition of the calculation gives a result close to that ofAlvarez, et al. [14].Google Scholar
28.Goldschmidt, V. M. 1954. Geochemistry. Clarendon; Oxford. 730 pp. See alsoParthé, E. and Crocket, J. H.1969-1978. Platinum group. In: Wedepohl, K. H., ed. Handbook of Geochemistry, vol. II-5, sec. 78. Springer-Verlag; New York.Google Scholar
29.Kucha, H. 1981. Quoted by Thierstein (GII) and others. The deposits are metalliferous and may come from oceanic hot springs.Google Scholar
30.Ruckledge, J. C. et al. Accelerator mass spectrometric (AMS) measurement of Pt and Ir at the Cretaceous-Tertiary boundary. Syllogeus. 39:147–149. In at least the Fiskeler at Stevns Klint, Denmark, the organic fraction with high Pt-group concentration is mostly dinoflagellate cysts [32]. There is too little organic material for all the Ir (Ruckledge [26, p. 100]), but most of it probably decayed (Thierstein [26, p. 101]) and the pyrite so induced does contain high Ir too. Moreover, Thierstein [26, p. 101] notes that sulfides can reoxidize with the return of oxidizing conditions, so the single exception known (the central part of the Danish basin) is ambiguous.Google Scholar
31.Kyte, F. T., Zhou, Z., and Wasson, J.T. 1980. Siderophileenriched sediments from the Cretaceous-Tertiary boundary. Nature. 288:651–656.CrossRefGoogle Scholar
32.Ruckledge, J. C., de Gasparis, S., and Norris, G. 1982. Stratigraphic applications of accelerator mass spectrometry using isotrace. Proc. 3d N. Am. Paleontol. Conv. 2:455–460.Google Scholar
33.Keith, M. L. 1982. Violet volcanism, stagnant oceans and some inferences regarding petroleum, strata-bound ores and mass extinctions. Geochim. Cosmochim. Acta. 46:2621–2637.Google Scholar
34.Ganapathy, R. 1982. Evidence for a major meteorite impact on the Earth 34 million years ago: implication for Eocene extinctions. Science. 216:885–886.Google Scholar
35.Alvarez, , Asaro, W. F., Michel, H. V., and Alvarez, L. W. 1982. Iridium anomaly approximately synchronous with terminal Eocene extinctions. Science. 216:886–888.CrossRefGoogle ScholarPubMed
36.That the impact (if any) itself was not on the Earth has been proposed byO'Keefe, J. A. 1980. The terminal Eocene event: formation of a ring system around the Earth? Nature. 285:309–311; 288:104.Google Scholar
37.The concentrations of zinc and tantalium show an equally good correlation with microtektite abundance, butAsaro, et al. (GII) do not discuss these.Google Scholar
38.Keller, G., D'Hondt, S., and Vallier, T. L. 1983. Multiple microtektite horizons in upper Eocene marine sediments: no evidence for mass extinctions. Science. 221:150–152.Google Scholar
39.The position of the Eocene-Oligocene boundary is disputed over a magnitude of several million years. This has been wryly summarized bySavage, D. E. and Russell, D. E. 1983. Mammalian Paleofaunas of the World. 432 pp. Addison-Wesley; Reading, Mass.Google Scholar
40.Possibly there is a problem with the stratigraphic correlation. There is no biological requirement that species appear and go extinct synchronously worldwide, and indeed there are many exceptions known. It is not dear whether such correlations, especially when based on single species' not forming lineages, should be preferred to correlations based on an Ir anomaly. Probably magnetostratigraphy will be able to resolve the issue here. Diachronous appearance of nannofossil species near K-Pg in different areas has been reported byRomein, A. J. T. 1977. Calcareous nannofossils from the Cretaceous-Tertiary boundary interval in the Barranco del Gredero (Caravaca, Prov. Murcia, S. E. Spain). Proc. Konink. Ned. Akad. Wetensch., Ser. B. 80:256–279.Google Scholar
41.Smit, J. and Klaver, G. 1981. Sanidine spherules at the Cretaceous-Tertiary boundary indicate a large impact event. Nature. 292:47–49.Google Scholar
42.Epstein, S., lecture reported byGrieve, R. A. F. 1982. Cosmic dust and impact events. Geotimes. 27(6):23–24.Google Scholar
43.Ganapathy, R. 1980. A major meteorite impact on the Earth 65 million years ago: evidence from the Cretaceous-Tertiary boundary clay. Science. 209:921–923.Google Scholar
44.O'Keefe, J. D. and Ahrens, T.J. 1982. Impact mechanics of the Cretaceous-Tertiary extinction bolide. Nature. 298:123–127.Google Scholar
45.Hsü, K. J. et al. 1982. Mass mortality and its environmental and evolutionary consequences. Science. 216:249–256.Google Scholar
46.Rampino, M. R. and Reynolds, R. C. 1983. Clay mineralogy of the Cretaceous-Tertiary extinction bolide. Nature. 298:123–127.Google Scholar
47.There is some diagenetic alteration; Varekamp and Thomas (GII) found some sanidine spherules at Caravaca, Spain, partly altered to clay, and other changes are likely [46]. A pure smectite at Nye Kløv, Denmark [46], could be an alteration product of either bentonite (volcanic ash), as seen a bit lower in the section, or glass from an impact [48]. Rampino (GII) says that if glass came from a meteorite it should be less than 20% of the fallout, not the total layer as here. This conclusion agrees with that from trace-element composition [25].Google Scholar
48.Kastner, M., work cited by F. Asaro [26, pp. 8–9].Google Scholar
49.Sadler, P. M. 1981. Sediment-accumulation rates and the completeness of stratigraphic sections. J. Geol. 89:569–584. Schindel, D. E.1983. Resolution analysis: a new approach to gaps in the fossil record. Paleobiology. 8 (for 1982):340-353. My value is calculated from figs. 4 and 5 of Sadler and fig. 1 of Schindel, and the probability declines with a greater overall interval.Google Scholar
50.Thierstein [26, p. 122] notes that most North Pacific hiatuses in the latest Cretaceous end “at the very base of the Paleocene.”Google Scholar
51.Even today, however, carbonate dissolves in some shallow waters: Alexandersson, E. T. 1975. Etch patterns on calcareous sediment grains: petrographic evidence of marine dissolution of carbonate minerals. Science. 189:47–48.Google Scholar
52.Tappan, H. 1968. Primary production, isotopes, extinctions and the atmosphere. Palaeogeog., Palaeoclim., Palaeoecol. 4:187–210.Google Scholar
53.Thierstein (GII) thinks the section at Caravaca, Spain, may represent turbidites because of its relatively rapid deposition, and argues from this against a change in the carbonate-compensation depth. Turbidites have an easily identifiable sedimentary pattern and have not been reported in the very detailed studies of the Caravaca section. In fact, their absence at the boundary in any section argues against a marine impact, as Smit (GII) argues for the Atlantic. There is, however, some syndepositional slumping at the Lattengebirge in southeast Bavaria (Perch-Nielsen et al., GII). Ahrens and O'Keefe [54] use the absence of turbidites to set an upper limit of 2 km on the diameter of any meteoroid. This is less than a third the value estimated by Alvarez et al. [11] by their single useful method, amount of Ir deposited. As this estimate used the kind of meteorite with the highest concentration of Ir (Parthé and Crockett in [28]) and a locality with a relatively low amount of Ir [6], the discrepancy may be more pronounced than stated. Hörz (GII) argues against an enormous and farcarrying wave from an impact.Google Scholar
54.Ahrens, T. J. and O'Keefe, J. D. 1983. Impact of an asteroid or comet in the ocean and extinction of terrestrial life. J. Geophys. Res. 88(suppl.):A799–A806.Google Scholar
55.Both data sets show a large drop in δ18O just above the boundary, although at slightly different horizons. Romein's values of δ18O in the basal Danian continue to be at or below the latest Maestrichtian values, though, while those of Perch-Nielsen et al. progressively increase to appreciably higher values and remain higher than Romein's. δ13C is even more discordant, with Romein's data showing a progressive decline while the other set declines abruptly at the boundary, then gradually increases, and then declines again. The spacing of samples, as given, does not account for these discrepancies.Google Scholar
56.Zimmerman, M. A., Williams, D. F., and Röttger, R. 1983. Symbiont-influenced isotopic disequilibrium in Heterostegina depressa. J. Foraminif. Res. 13:115–121.Google Scholar
57.McLean, D. M. [26, p. 47].Google Scholar
58.Chondrites have a very high δ13C, even beyond +50‰ (Hirner, A., 1979, cited by Hsü [17]), although comets theoretically may differ from them greatly and other meteorites are known to do so. This would appear to put some constraints on the δ13C of the boundary sediments, but the carbon of an impacting meteoroid (to 3.5% in type 1 carbonaceous chondrites: Hoefs, in Wedepohl [28], sec. 6c) may mostly be oxidized and so diluted by the larger atmospheric CO2 reservoir (2 × 1017 g).Google Scholar
59.Pollack, J. B., Toon, O. B., Ackerman, T. P., McKay, C. P., and Turco, R. P. 1983. Environmental effects of an impact-generated dust cloud: implications for the Cretaceous-Tertiary extinctions. Science. 219:287–289.Google Scholar
60.The dust may, however, be transported atmospherically over a period of several months rather than being ballistically propelled [44], although Jones and Kodis (GII) find the latter result. Atmospheric transport would make photosynthetically inhibiting darkness much shorter, ca. a month [59], and perhaps absent on a worldwide basis [6]. This case would not affect the problem of concentration of Ir in reduced materials, discussed above, because only about 10% of the impact-generated detritus would be less than 1 mm [44] or 1 μm (O'Keefe and Ahrens, GII) in diameter and so available for some atmospheric transport.Google Scholar
61.Béland, P. [26, p. 66]Google Scholar
62.Gilbert, W. S. 1880. The Pirates of Penzance.Google Scholar
63.Clube, S. V. M. and Napier, W. M. 1982. The role of episodic bombardment in geophysics. Earth Planet. Sci. Let. 57:251–262. The quotation is from p. 259.CrossRefGoogle Scholar
64.Emiliani, C., Kraus, E. B., and Shoemaker, B. M. 1982. Sudden death at the end of the Mesozoic. Earth Planet. Sci. Let. 55:317–334.Google Scholar
65.Turco, R. P., Toon, O. B., Park, C., Whitten, R. C., Bollack, J. B., and Noerdlinger, P. 1981. The Tunguska meteor fall of 1908: effects on stratospheric ozone. Science. 214:19–23.CrossRefGoogle ScholarPubMed
66.Sagan, C. 1973. Ultraviolet selection pressure on the earliest organisms. J. Theor. Biol. 39:195–200.Google Scholar
67.Such a volcanic cause has been advocated, among others, byHinz, K. 1981. A hypothesis on terrestrial catastrophes. Geol. Jb. Ser. E. 22:3–28.Google Scholar
68.Molnar, P. and Francheteau, J. 1975. Plate-tectonic and palaeomagnetic implications for the age of the Deccan Traps and the magnetic-anomaly time scale. Nature. 255:128–130. Alvarez, W.[26, p. 89] thinks the approximate contemporaneity could represent the site of an impact.Google Scholar
69.McLean, D. M. 1982. Deccan volcanism and the Cretaceous-Tertiary transition scenario: a unifying causal mechanism. Syllogeus. 39:143–144.Google Scholar
70.Vogt, P. R. 1972. Evidence for a global synchronism in mantle-plume convection and possible significance for geology. Nature. 240:338–342. Bentonites (volcanic-ash deposits) are abundant in the two areas I have seen, New Mexico and Montana, and in fact one occurs in Montana within a coal used locally to mark the K-Pg boundary (and its radiometric dating thereby provides one of the prime calibrations for the geologic time scale).Google Scholar
71.Varekamp and Thomas (GII) note an apparently negative relationship between the concentration of chalcophilic elements at K-Pg and distance from active spreading ridges. Ir is the most chalcophilic of the noble metals. Keith [33] would have volcanogenic chlorine destroy the ozone layer, which does not seem to be a necessary consequence, and so its refutation does not do further damage to the volcanism hypothesis.Google Scholar
72.Birkelund and Hakansson (GII) note that the soft-bottom colonizers which constitute the fauna of the Danish basal Danian would probably not have tolerated a large drop in salinity.Google Scholar
73.Vail, P. R., Mitchum, R. M. Jr., and Thompson, S. III. 1977. Seismic stratigraphy and global changes of sea level. 4. Global cycles of relative changes of sea level. Pp. 83–97. In: Payton, C. E., ed. Seismic Stratigraphy. Am. Assoc. Petrol. Geol. Mem.26.Google Scholar
74.Mörner, N.-A. 1980. Relative sea level, tectono-eustacy, geoidal-eustacy and geodynamics during the Cretaceous. Cretaceous Res. 1:329–340. Mörner, N.-A.1981. Revolution in Cretaceous sea-level analysis. Geology. 9:344-346. Mörner interprets the regression as from an increase in ocean-basin volume. This is presumably produced by a low rate of spreading from mid-ocean ridges, permitting cooling plates to sink more rapidly than they are replenished, although this mechanism may be too slow for the K-Pg regression. But where does the suboceanic material displaced by the additional weight of water above the sinking slab go? Is this where epeirogenies like the later one of the Great Plains (or the earlier ones of the oceanic plateaus, although here no regression would be involved) get their underpinning? Variable rates of interplate extrusion are presumably balanced penecontemporaneously by subduction.CrossRefGoogle Scholar
75.Unless an enriched and discrete burrow was a large part of the sample, more than half of the sediment underlying the boundary would have to consist of boundary material. Yet the two layers are discrete in a published photograph (best reproduced byHsü, et al., GII). Moreover, the lower sample contains 10 times as much CaCO3 as does the boundary sample. Therefore the putative burrow would have to be filled by material from an unusually limy boundary layer, which then would have to have almost all of its own CaCO3 (but not most of that in the burrow) dissolved. Resampling, if possible, with attention to sedimentary texture should show if this apparendy necessary scenario is correct. However, neither δ18O nor δ13C shows any signs of admixture; in fact the value of δ18O at −5 cm is lower than those for both the boundary and immediately subjacent latest Cretaceous samples.Google Scholar
76.Officer, C. B. and Drake, C. L.The Cretaceous-Tertiary transition. Science. 219:1383–1390. Alvarez, W. et al. (unpublished manuscript) attack other aspects of this paper rather fiercely. In a paper not cited, Gamper [77] found a gradual turnover of planktonic foraminiferans near Tampico, Mexico.Google Scholar
77.Gamper, M. A. 1977. Acerca del limite Cretacico-Terciario en Mexico. Rev. Univ. Nacion. Autón, México, Inst. Geol. 1:23–27.Google Scholar
78.Perhaps work on modern foraminiferans could shed light on relevant adaptive differences between smaller and larger planktonic species. Calling the larger ones more K-selected is no help and need not even be true. Are their algal symbionts relevant?.Google Scholar
79.This case of apparent multiple sympatric speciation, at the base of the whole adaptive radiation of Cenozoic planktonic foraminiferans, needs more detailed study and documentation. Whatever was happening should be interesting. Similar phenomena are occasionally reported for other planktonic foraminiferans.Google Scholar
80.An intermediate species, Globigerina minutula, “grades into” G. fringa, yet they both continue to coexist. Are they really discrete, or is the intergradation only at the origin of G. fringa? Olsson [81] believes that G. fringa comes from Hedbergella (or Globotruncanella) monmouthensis instead.Google Scholar
81.Olsson, R. K. 1982. Cenozoic planktonic Foraminifera: a paleobiogeographic summary. Pp. 127–147. In: Buzas, M. A. and Sen Gupta, B. K., eds. Foraminifera: Notes for a Short Course. Univ. Tennessee, Dept. Geol. Sci., Stud. Geol.6.Google Scholar
82.Wright, A., Heath, R., and Burckle, L. 1982. Glomar Challenger at the Cretaceous-Tertiary boundary. Nature. 299:208.Google Scholar
83.Smit (GII) considers some other reports of G. eugubina to be misidentifiations. Perhaps he would so consider this.Google Scholar
84.Van Valen, L. M. 1978. The beginning of the Age of Mammals. Evol. Theory. 4:45–80.Google Scholar
85.De Coninck, J. and Smit, J. 1982. Marine organic-walled microfossils at the Cretaceous-Tertiary boundary in the Barranco del Gredero (S.E. Spain). Geol. Mijnbouw. 61:173–178.Google Scholar
86.Schopf, T. J. M., Raup, D. M., Gould, S. J., and Simberloff, D. S. 1975. Genomic versus morphologic rates of evolution: influence of morphologic complexity. Paleobiology. 1:63–70.CrossRefGoogle Scholar
87.Riedel, W. R. and Sanfilippo, A. 1982. Evolutionary history of Cenozoic cyrtoid radiolarian genera. Proc. 3d N. Am. Paleontol. Conv. 2:429–434.Google Scholar
88.Antra, N. J. and Cheng, J. Y. 1970. The survival of axenic cultures of marine planktonic algae from prolonged exposure to darkness at 20°C. Phycologia. 9:179–184.Google Scholar
89.Tappan (GII) also notes that coccolithophores do better in nutrient-rich water than do dinoflagellates, that nitrate runoff from land and direct precipitation of NOx should enrich the sea after a collision, but that it was coccolithophores which were much more affected at K-Pg. The Cretaceous coccolithophores did survive a little past the boundary (Perch-Nielsen, et al., GII), but there is no reason to expect there to have been an enhancement of phosphate like that of nitrate.Google Scholar
90.At Zumaya, Spain, however, ammonites gradually disappear between 15 m and 10 m below the boundary: Ward, P. 1983. The extinction of the ammonites. Sci. Am. 249(4):136–147.Google Scholar
91.Smit (GII) also claims that about 20% of the benthic foraminiferans at Caravaca became locally extinct. As he included all species with as few as two specimens available but did not give data, it is unclear how much of this value may come from sampling error.Google Scholar
92.[93, p. 50]. The analysis was based on an unpublished compilation I have made which is considerably more detailed than any of those which have been published. The latter all contain appreciable errors with respect to the extinction, which of course does not exclude such errors in mine also.Google Scholar
93.Van Valen, L. M. and Sloan, R. E. 1977. Ecology and the extinction of the dinosaurs. Evol. Theory. 2:37–64. My own bias is to gradualism, a bias resulting from our data as summarized here.Google Scholar
94.Kauffman, E. G. 1979. The ecology and biogeography of the Cretaceous-Tertiary extinction event. In: Christensen, W. K. and Birkelund, T., eds. Proc. Cretaceous/Tertiary Boundary Events Symp. 2:29–37. Univ. Copenhagen.Google Scholar
95.Hickey, L. J. 1981. Land-plant evidence compatible with gradual, not catastrophic, change at the end of the Cretaceous. Nature. 292:529–531.Google Scholar
96.Newell, N. D. 1971. An outline history of tropical organic reefs. Am. Mus. Novitates. 2465:1–37. A Paleocene reef, age unspecified, has been reported by Babic, L., and J. Zupanič. 1981. Various pore types in a Paleocene reef, Banija, Yugoslavia. Soc. Econ. Paleontol. Mineral., Spec. Publ. 30:473-482.Google Scholar
97.Hsü, K. 1982. (Comment on report by C. L. Drake.)Geology. 10:557–558.Google Scholar
98.Jarzen, D. M. [26, pp. 48–51].Google Scholar
99.Orth, C. J., Gilmore, J. S., Knight, J. D., Pillmore, C. L., Tschudy, R. H., and Fassett, J. E. 1981. An iridium-abundance anomaly at the palynological Cretaceous-Tertiary boundary in northern New Mexico. Science. 214:1341–1343. The Ir anomaly in the Raton Basin has been reported to occur in a normal-polarity interval, the opposite polarity of that in most or all other sections studied [100]. D. L. Wolberg (personal communication) says that extensive tests have failed to make this polarity questionable. If it is correct, then there is more than one Ir anomaly near K-Pg.Google Scholar
100.Payne, M. L., Wolberg, D. L., and Hunt, A. A. 1982. Magnetostratigraphy [of the] Raton and San Juan Basins, New Mexico: Implications for synchroneity of Cretaceous-Tertiary boundary events. Abst. Prog. Geol. Soc. Am. 14:584.Google Scholar
101.Carol Williams, personal communication.Google Scholar
102.Shoemaker, R. E. 1966. Fossil leaves of the Hell Creek and Tullock Formations of eastern Montana. Palaeontographica B119:54–75. Norton, N. J., and Hall, J. W.1969. Palynology of the upper Cretaceous and lower Tertiary in the type locality of the Hell Creek Formation, Montana. Palaeontographica B125:1-64. Leffingwell, H. A.1971. Palynology of the Lance (late Cretaceous) and Fort Union (Paleocene) Formations of the type Lance area, Wyoming. Spec. Pap. Geol. Soc. Am. 127(for 1970): 1-64. Jarzen, D. M. [26, p. 48].Google Scholar
103.Sloan, R. E. 1964. Paleoecology of the Cretaceous-Tertiary transition in Montana. Science. 146:430. Sloan, R. E. and Van Valen, L. M.1965. Cretaceous mammals from Montana. Science. 148:220-227. Van Valen, L. M. and Sloan, R. E.1965. The earliest primates. Science. 130:743-745, 1796. Sloan, R. E.1970. Cretaceous and Paleocene terrestrial communities of western North America. Proc. N. Am. Paleontol. Conv., 1969, Sec. E, pp. 427–453. Van Valen, L. M. and Sloan, R. E.1972. Ecology and the extinction of the dinosaurs. Proc. 24th Int. Geol. Cong. 7:214. We also have much unpublished work in manuscript.Google Scholar
104.Clemens has corroborated and somewhat extended our work in collaboration with his former student Archibald and others. Clemens (GII) cites this set of papers. Because the latter papers have not emphasized our strongest evidence for a gradual transition, the evidence has seemed, to those who rely on these papers, weaker than it really is (see also 105).Google Scholar
105.Clemens, W. A., Archibald, J. D., and Hickey, L. J. 1981. Out with a whimper not a bang. Paleobiology. 7:293–298.Google Scholar
106.Whatever the mass of Titanopteryx (?=Quetzalcoatlus), at least most species of Pteranodon (the next largest) were presumably smaller than 25 kg: Bramwell, C. D., and Whitfield, G. R. 1974. Biomechanics of Pteranodon. Philos. Trans. Roy. Soc. Lond. B267:503–581. Elsewhere, Ahrens and O'Keefe [54] think that dinosaurs were entirely near-shore animals and so would be vulnerable to impact tsunamis. This is nonsense (e.g. Russell, GII).Google Scholar
107.Most or all K-Pg multituberculates were apparently arboreal [108] and some survivors were ancestral to arboreal forms of the Paleocene [108, 109] Arboreal species should be especially susceptible to an impact.Google Scholar
108.Jenkins, F. A. Jr. and Krause, D. W. 1983. Adaptations for climbing in North American multituberculates (Mammalia). Science. 220:712–715.Google Scholar
109.Sloan, R. E. 1981. Systematics of Paleocene multituberculates from the San Juan Basin, New Mexico. Pp. 127–160. In: Lucas, S. G., Rigby, J. K. Jr., and Kues, B. S., eds. Advances in San Juan Basin Paleontology. Albuquerque: Univ. New Mexico Press.Google Scholar
110.The K-Pg boundary is located at the (lower) Z coal, as determined not only by the local extinction of dinosaurs and their associated community but by an Ir peak reported by Alvarez [6] and Ruckledge et al. [30, 32]. However, two tables by the latter authors, apparently reporting the same data, differ appreciably from each other. Clemens (GII) doubts the marine-terrestrial correlation because a radiometric age from the boundary bed in Montana differs from the age assigned to the boundary in a marine-based paper. However, the ages in the latter paper come from correlation with ages of continental rocks, including those of Montana.Google Scholar
111.The Protungulatum community is preserved in channel deposits, the base of the earliest being about 35 m (or at least about 25 m) below K-Pg [112]. The mean rate of sedimentation was about 1 m per 9,000-12,000 years [76, 113], the rate perhaps a bit more in the coalless sediments of the Hell Creek Formation below the boundary. Channels are of course lower than their floodplains, except when large levees intervene, but overall sedimentation here was aggradational in a delta-like environment, not a regime of ravine cutting, so the channel deposits are not much older than the surrounding floodplain deposits at the same level. Russell's suggestion (GII) of ravines is also contraindicated by the composition and sequence of the faunas and the local stratigraphic section of Lupton et al. [112].Google Scholar
This was the time of the terminal Cretaceous regression, but the Rocky Mountains were rising and shedding sediments faster than the sediments were carried into the sea. This is how a large wedge of terrestrial sediments came to lap over the underlying marine sediments. The predominance of local tectonic movements over eustatic changes has been emphasized for the late Cretaceous of the Canadian interior byJeletzky, J. A. 1971. Marine Cretaceous biotic provinces and paleogeography of western and Arctic Canada: illustrated by a detailed study of ammonites. Pap. Geol. Survey Can. 7022:1–92.Google Scholar
112.Lupton, C., Gabriel, D., and West, R. M. 1980. Paleobiology and depositional setting of a late Cretaceous vertebrate locality, Hell Creek Formation, McCone County. Montana. Contrib. Geol. 18:117–126. This locality is on the top of a small hill and, although it is apparently the earliest one containing the Protungulatum community, its distance below the boundary can be estimated only indirectly.Google Scholar
113.Archibald, J. D., Butler, R. F., Lindsay, E. H., Clemens, W. A., and Dingus, L. 1982. Upper Cretaceous-Paleocene biostratigraphy and magnetostratigraphy, Hell Creek and Tullock Formations, northeastern Montana. Geology. 10:153–159. The data in this paper suggest that dinosaurs in the Bug Creek area survived appreciably longer than did those 80 km to the west, but none of the critical data significantly deviate from randomness.Google Scholar
114.The term “faunal-facies” is used instead of “community” byArchibald, J. D. 1982. A study of Mammalia and geology across the Cretaceous-Tertiary boundary in Garfield County, Montana. Univ. California Publ. Geol. Sci. 122:1–286. The terms are not synonyms. A faunal facies or assemblage is observed and collected, whereas the community which gave rise to it is inferred. In this case two communities contributed to the same faunal facies, so the difference affects one's interpretation of what happened.Google Scholar
115.The second-lowest fauna with the Protungulatum community, Bug Creek Anthills, is by far the largest fauna of Mesozoic mammals known anywhere, by number of specimens. (The putatively earlier fauna [112] has produced only 4 mammal specimens, while the later ones are of moderate size.) Thus additions of species in later faunas are real but losses are less clear-cut, although the Triceratops community as a whole does constitute progressively less of the assemblage. Alvarez [6] and Russell (GII) think that dinosaur remains are distributed randomly through the floodplain deposits of the Hell Creek Formation, while work of Sloan [93] indicates an appreciable drop in abundance higher in the section. There are, however, as yet no adequate data. Fragments are more numerous than collectable specimens, and there is no quantifiable information on amount of prospecting effort at different levels. Whether there was a real decline in dinosaur diversity in the last few million years of the Cretaceous, as there was for several marine taxa [92], is a difficult problem involving differential preservation of habitats and several other factors not yet quantifiable (Russell, GII; Clemens, GII). The decrease appearing in the data may therefore not be real, but it is in any case irrelevant to the final extinction. Alvarez [6] makes fun of the view of Clemens (e.g., GII) that dinosaur extinction occurred a little before the boundary. The view is based on the fact that, in all suitable sections, the last dinosaur specimens do occur somewhat below the boundary. Such a position of the last specimen (i.e., below the last real occurrence) is qualitatively to be expected because of the moderate scarcity of good specimens, but its significance cannot be judged quantitatively without adequate data on the distribution of specimens through the section. Alvarez [6] does seem, by his own calculation, to err either in his belief of random distribution of specimens or in the precise time of extinction, while Clemens could be correct in both of his contrary views, even on the unnecessarily poor data Alvarez used.Google Scholar
116.The use [114] of the term “Mantuan” to mean only faunas equivalent to that of Mantua creates an unnecessary ambiguity, because my definition of it [84] was for all the earliest Paleocene in North America when so recognizable by mammals. The evolutionary stage of the mammal fauna, which is how land-mammal ages are distinguished, is quite different from that of the overlying Puercan, a difference recognized even by Archibald (personal communication) as comparable to that between other land-mammal ages. Our disagreement is on whether such a short interval deserves its own name, although the Rancholabrean is probably shorter. Ambiguity can be avoided even by those who choose not to recognize a distinct age.Google Scholar
117.Dinosaurs occur in the Bug Creek assemblage, but so does all the rest of the Triceratops community, in about the same low proportion. The invading Protungulatum community initially occupied only near-stream areas.Google Scholar
118.Alvarez [6] assumed that there was no prior information on the location of an Ir peak. However, given (as he knew) that in marine sections it was at K-Pg, any cause producing one also on land would have some reasonable if indefinite likelihood of producing it at the terrestrial K-Pg. Thus his actual argument is merely against a chance effect, not against an integrated gradualism.Google Scholar
119.Archibald, J. D. and Clemens, W. A. 1982. Late Cretaceous extinctions. Am. Sci. 70:377–385.Google Scholar
120.Alvarez [6] spent two long pages making fun of Clemens's conclusion, yet by the total evidence Clemens and others are correct that dinosaurs disappeared detectably before the Ir anomaly. It is curious that Alvarez [6] did not even mention the best evidence, that of the numerous uncolleaable specimens, despite gleefully reporting several conversations with Clemens on the subject.Google Scholar
121.Hickey, L. J., West, R. M., Dawson, M. R., and Choi, D. 1983. Arctic terrestrial biota: paleomagnetic evidence for age disparity with mid-northern latitudes during the late Cretaceous and early Tertiary. Science. 221:1153–1156. The evidence given for unexpectedly early occurrence of Eocene mammals is much weaker than that for the pollen; in the former case I see the likelihood of misidentification of magnetozones as greater than the likelihood of early evolution of derived Eocene perissodactyls.Google Scholar
122.Raup, D. M. and Sepkoski, J. J. Jr. 1982. Mass extinctions in the marine fossil record. Science. 215:1501–1503. Sepkoski (GII) modifies the analysis a little in ways unimportant here.Google Scholar
123.The cyclic replenishment of meteoroids [16] is itself controversial (GII and [1]).Google Scholar
124.Using absolute numbers is directly comparable to using the absolute number of deaths in a fluctuating population to determine the most dangerous times. There are more deaths, or extinctions, to be expected when more individuals or taxa are at risk. Probabilities of single events like these are meaningful, although they are not meaningful in the frequentist interpretation of probability.Google Scholar
125.Van Valen, L. M. 1984. A resetting of Phanerozoic community evolution. Nature. 307:50–52.Google Scholar
126.Extinctions can occur together in much shorter intervals than a stage, the smallest practical interval to use in such an analysis, as they do at K-Pg. The real probability per unit time for such short intervals would then be abnormally high, as would be the case for Cambrian biomere extinctions (Palmer, GII) if these are geographically synchronous. Hsü et al. (GII, [97]) propose a measure of extinction magnitude which could easily be modified to fit this perspective.Google Scholar
127.There is, though, a major extinction of the Famennian ammonite radiation at the end of the Famennian, according to the Treatise on Invertebrate Paleontology. Pedder (GII) notes that the many corals which became extinct in the Frasnian lived mostly in shallow water, so perhaps they were parts of mutualistic quasi species with unknown algae, like recent hermatypic corals.Google Scholar
128.McLaren, D. J. 1983. Bolides and biostratigraphy. Bull. Geol. Soc. Am. 94:313–324.Google Scholar
129.Van Valen, L. M. 1970. Late Pleistocene extinctions. Proc. N. Am. Paleontol. Conv., 1969, Sec. E, pp. 469–485.Google Scholar
130.Vogt, P. R. and Holden, J. C. 1979. The end-Cretaceous extinctions: a study of the multiple-working-hypotheses method gone mad. In: Christensen, W. K. and Birkelund, T., eds. Proc. Cretaceous/Tertiary Boundary Events Symp. 2:49.Google Scholar
131.Zoller, W. H., Parrington, J. R., and Kotra, J. M. P. 1983. Iridium enrichment in airborne particles from Kilauea volcano: January 1983. Science. 222:1118–1121.Google Scholar
132.See [25] and Varekamp and Thomas (GII). Other elements enriched in the Kilauea dust seem not to have been tested for at K-Pg, notably cadmium and indium.Google Scholar
133.Luck, J. M. and Turekian, K. K. 1983. Osmium-187/Osmium-186 in manganese nodules and the Cretaceous-Tertiary boundary. Science. 222:613–615.Google Scholar
134.Montanari, A., Hay, R. L., Alvarez, W., Asaro, F., Michel, H. V., Alvarez, L. W., and Smit, J. 1983. Spheroids at the Cretaceous-Tertiary boundary are altered impact droplets of basaltic composition. Geology. 11:668–671.2.0.CO;2>CrossRefGoogle Scholar
135.Turco, R. P., Toon, O. B., Ackerman, T. P., Pollack, J. B., and Sagan, C. 1983. Nuclear winter: global consequences of multiple nuclear explosions. Science. 22:1283–1292.Google Scholar
136.Kerr, R. A. 1983. Isotopes add support for asteroid impact. Science. 222:603–604.Google Scholar
137.This is Contribution 33 from the Lothlorien Laboratory of Evolutionary Biology.Google Scholar