Author: Unknown Title: Varves Indicate Older Earth than Creationists Allow Young-earth cre

Master Index Current Directory Index Go to SkepticTank Go to Human Rights activist Keith Henson Go to Scientology cult

Skeptic Tank!

====================================================================== Author: Unknown Title: Varves Indicate Older Earth than Creationists Allow ====================================================================== Young-earth creationists believe that the earth is less than a few hundred thousand years old. The following infor- mation about ancient varves gives strong evidence that the earth is _at least_ hundreds of millions of years old. _Ice Ages: Solving the Mystery_ [1] describes the fasci- nating discovery in the 1970s of the correlation between ice age climate cycles and variations in the earth's orbit. In the first half of the 20th century Milutin Milankovitch worked out an astronomical theory of how the orbital cycles affected climate. Later, others expanded on his work and correlated climate related data found in ocean bottom sedi- ment cores with the astronomical cycles. The cycles pre- dicted by Milankovitch's theory and discovered in the ocean sediments turned out to have the longest variation at 100,000 years, with shorter variations superimposed at about 41,000, 23,000 and 19,000 years. The book described the confirmation of the correlation: .... According to the expanded version of the astro- nomical theory developed by Mesolella and Kukla, cli- matic oscillations should occur as four distinct cycles: a 100,000-year cycle corresponding to varia- tions in eccentricity; a 41,000-year cycle correspond- ing to variations in axial tilt; and 23,000- and 19,000-year cycles corresponding to variations in pre- cession. In the summer of 1974, Imbrie performed the long-awaited test. Spectral analysis indicated that, as expected, the dominant climatic pulse was a 100,000-year cycle, which appeared on both the iso- topic and the radiolarian spectra as a large peak. But three other peaks--smaller but nevertheless dis- tinct--also appeared on the spectra (Figure 42). On the isotopic spectrum these cycles were 43,000 years, 24,000 years, and 19,000 years long. On the tempera- ture-radiolarian spectrum, they were 42,000 years, 23,000 years, and 20,000 years long. These results were everything for which Imbrie and his colleagues had hoped. Each of the cycles found in the Indian Ocean cores matched the predicted cycles within five percent. That such a coincidence might occur by chance alone seemed highly unlikely. Before long, Nicklas G. Pisias provided additional evidence in sup- port of the astronomical theory. Using a more power- ful spectral method, he found a statistically signifi- cant 23,000-year cycle in core V28-238. CLIMAP inves- tigators--realizing that their isotope records from the Pacific and Indian oceans matched the correspond- ing parts of isotope records already known from other __________________________ 1 John Imbrie and Katherine Palmer Imbrie, _Ice Ages: Solving the Mystery_, pp. 167-173, Enslow Publishers, Short Hills, New Jersey, 1979. - 2 - oceans--felt justified in concluding that the succes- sion of late Pleistocene ice ages had indeed been triggered by changes in the earth's eccentricity, pre- cession, and tilt.... Convinced now that major climatic changes were caused by astronomical variations, and that the 41,000-year and 23,000-year climatic cycles followed systemati- cally behind variations in tilt and precession, Hays, Imbrie, and Shackleton announced their findings in an article in _Science,_ which appeared on December 10, 1976: "Variations in the Earth's Orbit: Pacemaker of the Ice Ages." A century after Croll published his theory and 50 years after Milankovitch mailed his radiation curves to Koppen and Wegener, two cores from the Indian Ocean confirmed the astronomical theory of the ice ages. At last, geologists had clear evidence that the motions of the earth in its orbit around the sun triggered the succession of late Pleistocene ice ages. Exactly how this triggering mechanism operated, and why the 100,000-year cycle of orbital eccentricity appeared to be so strongly impressed on the climatic record of the last half-million years were still unknown. But, for the moment, it was enough to know that Milutin Milankovitch, traveler through distant worlds and times, had led the way to solving a major part of the ice-age mystery.... It is amazing that Milankovitch's mathematical theory, first published about 1920, could be so accurately confirmed 50 years later by two independent geological phenomena. This theory was further confirmed in a most unusual way. _The Innocent Assassins_ describes how lake varves of two types form today, and then describes what was found in simi- lar ancient lakes: [2] During the Eocene epoch, a lake basin formed in North America, covering large parts of what are now the states of Colorado, Wyoming, and Utah. The area had previously been traversed by rivers flowing east, but in connection with the rise of the Rocky Mountains a barrier was formed to the east. Thus arose Fossil Lake, and waxed greater and greater, finally to cover an area of about 13,000 square kilometers, with a depth of up to 100 meters. It was thus about half the size of Lake Erie, and twice that of Great Salt Lake. Judging from the sediments that lie beneath and above those of Fossil lake, it existed for about one-third __________________________ 2 Bjorn Kurten, _The Innocent Assassins_, pp. 88-94, Columbia University Press, New York, 1991. - 3 - of the Eocene epoch. The lake-bottom sediments show a fine lamination with alternating light, lime-rich bands and dark ones containing a great deal of organic matter. There is also rich fossil flora and fauna (especially fish and insects). The flora indicate a climate of a subtropical type with two annual rainy seasons, and if the varves are interpreted on that basis (two dark bands to a year), it can be seen that the entire pile of sediments was formed during a time period of 6.5 million years. According to radiometric dating, the Eocene epoch started about 55 million years ago, and ended about 35 million years ago. Its total duration would then be about 20 million years. One-third of that is 6.7 mil- lion years, or very close to the number of years that can be counted in the lake-bottom silts of Fossil Lake. The agreement is almost too good to be true, but there you are. Radiometric dating is supported by the chronology based on annual varves. The longest consecutive sequence of annual varves that I have happened upon, in a far from systematic search, comes from eastern North America and constitutes about 40 million years. It dates from the later part of the Triassic period and the early part of the Jurassic period, and so has an age of about 220-180 million years before the present. My authority is Paul E. Olsen. The geography of the earth at the beginning of the Triassic period was very unlike that of the present day. All continents were then collected into a single supercontinent, called Pangaea ("all land"). Then began the birth of the Atlantic: a great rift valley running in a northeast-southwest direction started to form. It has its counterpart in the present-day Rift Valley of East Africa, which also marks the place of a future ocean. The Triassic valley, a string of at least thirteen elongated basins, extended from Nova Scotia to North Carolina. In the basins, very fine- grained lake sediments were deposited (forming the so- called Newark Supergroup) with annual laminae, total- ing some 40 million. Parts of the rift valley are now covered by the sea, but the southern part is dry, as are patches further north. The sediments preserve a record of climatic changes, especially an alternation between dry periods, when the water was low, and times of high precipitation and high waterlines. During the former, annual varves tend to be very thin, drying cracks are formed, and there are numerous footprints of reptiles, in some cases so perfectly preserved that you can count the - 4 - scales on the soles. At high water, the drying cracks are absent, and the sediments contain a great amount of organic matter, especially fish remains. As it happens now, these climatic changes are cycli- cal: they tend to return at regular intervals. Their periodicity is complicated, however, because it is a combination of several cycles differing in length. (Each cycle represents a sequence from low through high to low water.) The most important periods are about 25,000, 44,000, 100,000, and 400,000 years in length, respectively. These are figures that cause the geochronologist to smile in recognition. They have to do with changes in the rotation of the earth around the sun, (Note how closely the numbers match those of the Milankovitch cycles previously found for the recent Ice Ages) known from astronomical calculations, and have turned out to drive the climatic changes during the Ice Age as well--that is, during the last two million years or so of earth history. Now the analysis of the Newark Supergroup sediments proves that the same factors affected climates as long as 200 million years ago. And so the geological time scale, originally dated by radiometry, is corroborated by two additional and com- pletely independent methods of study: from analysis of annual varves, and from astronomical observations. The preceding descriptions of the confirmation of the Milankovitch theory and its correlation to ancient lake sed- iment layers is unequivocal evidence that the ice ages really occurred, and that the earth has existed for many hundreds of millions of years. It provides a striking con- firmation of the validity of radiometric dating techniques.


E-Mail Fredric L. Rice / The Skeptic Tank