CATASTROPHES AND EARTH HISTORY

Leonard Brand
Loma Linda University

Geoscience Reports 17:1-4 (Winter 1994).
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    The science of geology has abandoned Charles Lyell's rigid uniformitarianism, and is recognizing the important role of catastrophe in earth history.
    Early in the history of geology, in the 1700s and early 1800s, many geologists were catastrophists. They interpreted the rocks as having formed by catastrophic processes, and for some of them the Scriptures, with its account of creation and Noah's flood, was the basis for their geologic theories (Albritton 1989, Huggett 1990). Geological theories began to change, and the two geologists who were the most influential in replacing the catastrophic view of history were James Hutton and Charles Lyell.
    Lyell, in his book Principles of Geology (1830-1833), defined the concept of uniformitarianism that dominated geology for a century. Uniformitarianism, as defined by Lyell included four concepts (Gould 1984): 1) the laws of nature have always been the same, 2) the same geologic processes that we observe today have been responsible for all geologic events in past history, 3) geologic processes have always acted at the same slow, steady rates through eons of time (=gradualism), and 4) the earth has been in a steady state, with no directionality to geologic or biologic processes.
    Lyell's uniformitarianism soon eclipsed other theories, and in the succeeding decades no hypotheses involving catastrophic explanations for geologic features had any chance of being taken seriously. This episode has traditionally been seen as the triumph of a valid scientific theory over religious bias. A re-examination (Gould 1984, Rudwick 1972) has led to the conclusion that the biblical catastrophists were more careful scientists than Lyell and the other uniformitarians. Gould and Rudwick would not agree with the biblical flood concept that inspired many of the early catastrophists, but they point out that the catastrophists were careful, objective scientists in their analysis of data. Research in the last three decades has revealed that the data support the catastrophists in some important respects, more than they support Lyell. Modern geology still accepts the first two uniformitarian concepts: the laws of nature have always been the same, and the same geologic processes that we observe today (e.g., deposition of sediments by wind and water) have also been important in the past. However, the accumulating data no longer support Lyell's third and fourth concepts. The geologic record did not form primarily by Lyell's slow, steady, gradualistic process of rain and wind and weather changes wearing away the rock and slowly, steadily depositing new sediments. Catastrophic processes have been important agents in shaping the earth's geologic features, and the earth has not obeyed Lyell's steady-state policy, but the earth has changed considerably through time.
    The difference between Lyell and the catastrophists of his time was that the catastrophists were more careful observers of the rocks, while Lyell took a culturally derived gradualistic philosophy (geologic processes always operate at slow, steady rates) and imposed it upon nature. "Gradualism was never 'proved from the rocks' by Lyell and Darwin, but was rather imposed as a bias upon nature." "Lyell won with rhetoric what he could not carry with data" (Gould 1984, pp. 14 & 16). The modern science of geology still believes that the geologic record formed over hundreds of millions of years — a time scale that is in fact required for those who believe that all of life formed through the evolution process. However, it is now recognized that Lyell's rigidly gradualistic uniformitarianism "has had a profoundly negative impact by stifling hypotheses and by closing the minds of a profession toward reasonable empirical alternatives to the dogma of gradualism" (Gould 1984, p. 15).
    An intertwining system of canyons or coulees carved across the landscape of eastern Washington State played an important role in breaking the stranglehold of gradualism on the science of geology (Baker 1978, Gould 1984). In the 1920s the geologist J. Harlan Bretz began studying this area, called the Channeled Scablands (see photo below), and found evidence that the canyons were not cut slowly, but formed rapidly by a single gigantic flood. He presented papers at geology meetings, but other geologists rejected his hypothesis and tried to explain the scablands by ordinary, less violent mechanisms. Finally, in the 1950s a source for the flood waters was found — the enormous glacial Lake Missoula that filled the valleys in the Rocky Mountains in northern Idaho and northwestern Montana. Apparently an ice dam had broken and the waters of Lake Missoula catastrophically drained across eastern Washington, carving 1,000' deep canyons through the Columbia River Basalt Formation in a few days. This is believed to have happened several times. By the mid 1960s Bretz's catastrophic hypothesis was fully accepted, and other geologists began recognizing, at an accelerating pace, other evidence in the rocks that point to catastrophic processes, some of which were global in scale.

Scablands. (Photo courtesy Elaine Kennedy)

    Turbidites, the sedimentary deposits that form in minutes by the flow of water-saturated sediments down underwater slopes, are a significant feature of the geologic record (see photo below). Turbidity currents can flow down very slight slopes or even on the level after they develop momentum, and these flows have produced modern submarine fields of turbidites at the mouths of some large rivers that cover thousands of square miles. Turbidite fields cover 12,000 mi² off the mouth of the Mississippi River, 8,000 mi² at the Hudson River, and 20,000 mi² at the Congo River. Since the discovery of turbidites, many thousands of sedimentary deposits that were formerly interpreted as slow, gradual sediment accumulations have been reinterpreted as turbidites. This trend is so significant that it has been called the turbidite revolution (Walker 1973). Some turbidites carry large rocks along with them, and it has been estimated that clasts up to 100 metric tons can be moved by turbidites. Turbidites containing clasts more than one meter in diameter are found in several areas including the western United States, Arabia, and New Hebrides.

Turbidite. (Photo courtesy Elaine Kennedy)

    Debris flows are slower, less fluid flows that do not require a steep slope and can carry clasts of apparently unlimited size. Some exotic blocks have been moved long distances, often tens of kilometers, and up to several hundred kilometers (Chadwick 1978, Conaghan et al. 1976).
    Megabreccias are another fascinating type of sedimentary deposit in which angular rocks (clasts) greater than one meter in diameter occur in a matrix of finer material and smaller rocks (see photo below). Chadwick (1978) reviewed the literature on a number of very impressive megabreccia deposits. Most of these deposits are considered to have occurred under water, where buoyancy can reduce the weight of the rocks by 1/3 and can reduce friction.

Megabreccia. (Photo courtesy Ariel Roth)

    The increasing recognition of catastrophic deposits has been accompanied by recognition of other geological phenomena that may or may not be catastrophic, but show fascinating worldwide uniformity. Ager (1981) in his book The Nature of the Stratigraphical Record describes features of specific parts of the geologic column that are found over very large geographic areas or even worldwide. For example, at the base of the Cambrian there is a basal quartzite that is found virtually everywhere, typically followed by orthoquartzite, then glauconitic sandstones, and then marine shales and thin limestones. At the base of the Ordovician there also are prominent quartzites found in many parts of Europe, in Africa, and possibly more widespread than that. In the Devonian there are continental red sandstones that extend from eastern Canada all the way to Iceland, and through northern Europe to Russia. In Upper Devonian are found limestone reefs with characteristic types of fossils that occur through Europe, in northern Africa, North America, and Australia. The Mississippian Redwall Limestone is a prominent cliff-forming layer in the Grand Canyon. The same type of limestone formation, with similar fossils, is typical of the Lower Carboniferous throughout much of North America as far as Alaska, and across Europe and into Asia. Upper Carboniferous coal deposits are similar in fundamental ways, with similar fossil content, from eastern North America all the way into Russia. That is a distribution of coal deposits that covers 170º of longitude (at the same latitudes as those of eastern North America and Russia today; 130º when adjusted for plate movement). The Triassic in western North America is characterized by a series of redbeds, or red-stained formations. Series of characteristic Triassic redbeds are also found in eastern North America, across Europe, in Mexico and possibly other areas, with very similar characteristics in these widespread locations. Chalk is a very unusual sediment — a very pure coccolith (calcareous skeletal remains of a marine planktonic biflagellate algae) limestone that is only found at restricted levels in the geologic column. The white cliffs of Dover are an Upper Cretaceous chalk containing black flints in England. Virtually the same formation occurs in the Upper Cretaceous from Ireland through many parts of Europe into southern Russia, across the southern United States, and in Australia, with the same black flints and characteristic fossils. "There has been no other deposit quite like it before or since, except perhaps some Miocene chalks ..." (Ager 1981), which are also widespread. Ager only described deposits that he had personally seen, and thus it may be that some of these unique rock formations are much more widespread than what he had described. In summary, in different parts of the geologic column are characteristic deposits that cover very extensive geographic areas, and are often identifiably different from sediments in other parts of the column.
    Such geographically extensive formations are a common feature of the Paleozoic and Mesozoic rocks, but in the modern world the types of environments that presumably produced these sedimentary deposits cover relatively small areas. There are virtually no modern analogues for such extensive formation. The tremendous geographic extent of many Paleozoic and Mesozoic deposits is so out of character with the depositional environments that occur today that they almost beg for a very different explanation than can be supplied by modern analogues.
    Study of the rock record on a large scale has identified an interesting pattern (see figure below), of six cycles of sedimentation across the North American continent, separated in midcontinent by unconformities or times not represented by any rocks (Dott and Batten 1988). The same pattern seems to continue worldwide, with some variation in details (Dott and Batten 1988). This phenomenon merits much more study and the implications with respect to catastrophism are not yet fully understood.

Rock record and major unconformities across North America (after Dott and Batten 1988). The arrows along the left side indicate mass extinctions (data from Albritton 1989).

    At several levels in the fossil record there occur mass extinctions of animals (see figure, along the left side). At each of these mass extinctions many groups of animals that were common as fossils come to an end and do not appear again in the fossil record. The most famous of these worldwide mass extinctions is found at the top of the Cretaceous. At this point the dinosaurs and other large Mesozoic reptiles disappear, along with many types of marine invertebrate animals. With the increasing recognition of catastrophic processes in earth history, it has become widely accepted that at least some of these extinctions were probably caused by catastrophic events (see Glen 1990, Gore 1989, Gould 1989). A popular hypothesis is that some extinctions resulted from the impact of meteorites or asteroids on the earth. Such catastrophic events would never have been seriously considered by science 40 years ago, but the evidence has led to the recognition that catastrophic events have played an important part in shaping the earth's crust in the past.

LITERATURE CITED

• Ager, D. V. 1981. The Nature of the Stratigraphical Record. John Wiley and Sons, NY.
• Albritton, C. C., Jr. 1989. Catastrophic Episodes in Earth History. Chapman and Hall, NY.
• Baker, V. R. 1978. The Spokane flood controversy and the Martian outflow channels. Science 202:1249-1256.
• Chadwick, A. V. 1978. Megabreccias: evidence for catastrophism. Origins 5:39-46.
• Conaghan, P. J., E. W. Mountjoy, D. R. Edgecombe, J. A. Talent, and D. E. Owen. 1976. Nyubrigyn algal reefs (Devonian), eastern Australia: allochthonous blocks and megabreccias. Geological Society of America Bulletin 87:515-530.
• Dott, R. H., Jr., and R. L. Batten. 1988. Evolution of the Earth. McGraw-Hill Book Co., NY.
• Glen, W. 1990. What killed the dinosaurs? American Scientist 78:354-370.
• Gore, R. 1989. Extinctions. National Geographic 175(6):662-698.
• Gould, S. J. 1984. Toward the vindication of punctional change. In Berggren, W. A. and J. A. Van Couvering (eds.), Catastrophes and Earth History: The New Uniformitarianism. Princeton University Press, Princeton, NJ.
• Gould, S. J. 1989. An asteroid to die for. Discover 10(10):60-65.
• Huggett, R. 1990. Catastrophism: Systems of Earth History. Edward Arnold, NY.
• Rudwick, M. J. S. 1972. The Meaning of Fossils: Episodes in the History of Paleontology. McDonald, NY.
• Walker, R. G. 1973. Mopping up the turbidite mess. In R. N. Ginsburg, (ed.), Evolving Concepts in Sedimentology. Johns Hopkins University Press, Baltimore, MD.