first_imgGeochronology is a perverse sort of game.  Like the proverbial clock shop apprentice who went crazy trying to get all the grandfather clocks to tick together, the scientist trying to interpolate earth’s past climate patterns from geochronometers has so many uncooperative variables, he can never hope for anything better than partial conformity to accepted visions of Earth’s history.    Gideon M. Henderson, writing in the Aug. 4 issue of Science,1 provided some insight into the messy process while advertising cave formations as his chronometer of choice.  Other geochronologists have relied on ice cores, deep sea sediments, and orbital mechanics to draw their timelines and work their models.  In promoting cave formations (speleothems), Henderson inadvertently deprecated the leading alternatives.  Those who thought ice cores and sediment patterns produce accurate pictures of past geoclimatic events may be in for a surprise.  He began:When you check the weather forecast on TV, you do not expect it to be completely accurate.  But you do expect a degree of certainty about when the forecast is for: It would not be very useful to hear that it will probably be rainy, but with a thousand-year uncertainty about when.  Yet this is the situation faced by those studying past climate.  Records of climate from sediment or ice cores are not time series but depth series, and converting depth to age generally carries a substantial uncertainty.Later, he again criticized ice core dating methods, often considered the gold standard for ice-age dates, with a good-news bad-news jab:Drilling into high-latitude and high-altitude ice sheets has revolutionized our understanding of climate, particularly at time scales of millennia and shorter.  Such records have taught us how abruptly climate can change; they have provided unique records of past atmospheric composition; and they will doubtless continue to enlighten us    But ice cores do have limitations.  They are found far from major human populations, they do not capture variability in major climate systems such as the monsoons or El Niño, and they are difficult to date accurately.Against this foil, of course, Henderson sold his speleothems as superior geochronometers because they can be radiometrically dated (but compare 01/19/2006 and 01/12/2005, and 10/06/2004 and 09/24/2004 entries).  The prior week, however, Science had no less than four articles on geochronology, and none of them even mentioned cave formations.  Didier Paillard, in his Perspective piece on ice age dating,2 lowered the confidence level even further by detailing the mismatches between commonly trusted geochronometers:The exposure of Earth’s surface to the Sun’s rays (or insolation) varies on time scales of thousands of years as a result of regular changes in Earth’s orbit around the Sun (eccentricity), in the tilt of Earth’s axis (obliquity), and in the direction of Earth’s axis of rotation (precession).  According to the Milankovitch theory, these insolation changes drive the glacial cycles that have dominated Earth’s climate for the past 3 million years.    For example, between 3 and 1 million years before present (late Pliocene to early Pleistocene, hereafter LP-EP), the glacial oscillations followed a 41,000-year cycle.  These oscillations correspond to insolation changes driven by obliquity changes.  But during this time, precession-driven changes in insolation on a 23,000-year cycle were much stronger than the obliquity-driven changes.  Why is the glacial record for the LP-EP dominated by obliquity, rather than by the stronger precessional forcing?  How should the Milankovitch theory be adapted to account for this “41,000-year paradox”?Paillard referred to the two possible solutions published in the same July 28 issue of Science, the details of which can be left to the interested reader.  Neither, however, came out a clear-cut winner.  The solution might be one, or the other, or a combination: but in accepting any of the alternatives, one must discard previously trusted basic principles:Two different solutions are presented in this issue.  The first involves a rethinking of how the insolation forcing should be defined, whereas the second suggests that the Antarctic ice sheet may play an important role.  The two papers question some basic principles that are often accepted without debate.Both models, Paillard continued, question one or another “pillar of ice age research” in the attempt to achieve congruity (cp. 02/02/2005 story).  Each may be part of the solution, he hoped, but had to face the mismatches head on:Still, neither hypothesis can account for the beginning of Northern Hemisphere glaciations around 3 million years ago.  Furthermore, during the past 1 million years, glacial-interglacial oscillations have largely been dominated by a 100,000-year periodicity, yet there is no notable associated 100,000-year insolation forcing.  There is currently no consensus on what drives these late Pleistocene 100,000-year cycles.Scientists have debated these things since the days of von Humboldt and Lyell in the 19th century, Paillard reminded the reader.  Milankovitch belonged to a group claiming insolation drove glacial cycles, while Tyndall and Arrhenius argued that atmospheric CO2 was responsible.  Things have only gotten messier since then:The big challenge is to build an ice age theory that can account not only for ice sheet and atmospheric CO2 changes, but also for the start of glaciations about 3 million years ago and for the transition from 41,000-year cycles to much larger 100,000-year oscillations around 1 million years ago.  The atmospheric CO2 concentration was probably very important over the past 1 million years, but was this also the case during the LP-EP?  Alternatively, if one can build a purely insolation-based theory between 3 and 1 million years ago, as suggested by Huybers and Raymo et al., why is this not the case anymore in the past 1 million years?In an attempt to remain upbeat, Paillard mentioned a possible “conceptual model” that has the ocean alternately storing and burping atmospheric carbon dioxide depending on ice-sheet size and insolation.  That, comparing favorably with “more sophisticated models,” provides “a framework for understanding the likely climatic future of our planet in the context of the climate of the past 3 million years,” he claimed.  Yet it would seem that future extrapolations would be even more prone to error than past extrapolations.    Paillard failed to mention a more serious issue.  No human observer ever witnessed a full cycle of glacial oscillations or Milankovitch cycles.  Written records only go back some 6,000 years.  The large cycle values mentioned matter-of-factly are extrapolated backward into the past from current measurements by orders of magnitude, or interpolated from the acceptance of the standard evolutionary geologic column (05/13/2004) and estimates of the age of the solar system (06/05/2003).  The degree of confidence one can have in those estimates is left as an exercise (see 03/05/2004, 10/09/2003).1Gideon M. Henderson, “Perspectives: Climate: Caving In to New Chronologies,” Science, 4 August 2006: Vol. 313. no. 5787, pp. 620-622, DOI: 10.1126/science.1128980.2Didier Paillard, “What Drives the Ice Age Cycle?” Science, 28 July 2006: Vol. 313. no. 5786, pp. 455-456, DOI: 10.1126/science.1131297.If you have been led to believe that ice-core dating, Milankovitch cycles and deep sea sediments provide reliable records of Earth’s prehistory, this entry should hit you with a proverbial two by four.  The records don’t match up naturally.  Scientists attempt to force a match with “sophisticated” and “conceptual” models that provide the best of bad solutions (see best-in-field fallacy).  Taking the A.S.S. (age of the solar system) as an unalterable boundary condition (because a younger Earth would utterly preclude Darwinian evolution), they find themselves in a bind.  Their faith forces them to believe there is a solution, but the data don’t fit.  No problem; the goal of life now is to keep the detective game going, not to really know the truth about reality past.    Each rigger has his role in the endless game.  The Darwinist astronomy wizards prophesy the date when the earth cooled 4.5 billion years ago, the Darwinist origin-of-life wizards prophesy the date life appeared 3 billion years ago, the Darwinist geochemist wizards prophesy when life began to produce oxygen two billion years ago, and the Darwinist paleoanthropologist wizards prophesy when Homo habilis appeared and what kind of clothes he was wearing 3 million years ago.  In between these posts of straw, they string their tabernacle to Charlie, hoping they can keep the whole structure from falling down with enough researchers pushing and pulling where needed.    We just thought you should know how the process works.  Because the Darwinists are master riggers, everything makes sense, the wizards and priests remain employed, textbooks have nice graphics, students memorize the currently accepted dates, Charlie gets the glory, and nobody asks questions.(Visited 9 times, 1 visits today)FacebookTwitterPinterestSave分享0last_img

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