The Andes: Pop-Up Mountains

The majestic Andes of South America did not rise smoothly and gradually, a team of geologists reported in Science.¹  Instead, long periods of stasis for tens of millions of years were punctuated by rapid periods of uplift.  It sounds as if punctuated equilibria theory has been stolen from evolutionary biology and applied to geology.  They say the Andes – the second largest mountain chain in the world – could have risen over 2 km in about a million years.
    The authors explain this erratic motion by saying, “Periodic punctuated surface uplift of mountain belts probably reflects the rapid removal of unstable, dense lower lithosphere after long-term thickening of the crust and lithospheric mantle.”  It had “long been thought” that shortening and thickening of continental crust gave rise to mountains, they said.  Now, however, they think that measurements of surface isotopes show that the two processes don’t seem to work together so should be worked out separately.
    The international team measured various factors – amount of erosion, outgassing from volcanoes, isotope ratios in clays and carbonates, and sediment thicknesses.  They took into account “paleo-elevation data” tying each stratum’s position in the geologic column in relation to its elevation.  They plugged the values into models in an attempt to infer the history of the mountain range.  Other assumptions, such as climate history and behavior of the upper mantle, were included.
    Richard A. Kerr summarized the paper in the same issue of Science,² titling his article, “The Andes popped up by losing their deep-seated rocky load.”  One problem he noted about the pop-up theory is that crustal compression doesn’t happen that fast.  The team explained it by suggesting that a section of “ballast” under the mountains might have fallen away into the mantle, allowing the rapid rise above.  “The timing and style of volcanism in the central Andes suggest that the mantle lithosphere fell away suddenly–as a huge drop dripping off the crust or as a layer peeling away–just when the isotopic data indicate a punctuated uplift,” he said.
    Other geologists are not convinced.  One, for instance, thinks that the rise of the mountains alters the climate and can give false paleo-elevation data.  Some wish to rely more on models; some wish to give more weight to field data.  For a popular write-up of the new theory, see Science Daily, which begins, “Mountains may experience a ‘growth spurt’ that can double their heights in as little as two to four million years–several times faster than the prevailing tectonic theory suggests.”

1.  Garzione et al, “Rise of the Andes,” Science, 6 June 2008: Vol. 320. no. 5881, pp. 1304-1307, DOI: 10.1126/science.1148615.
2.  Richard A. Kerr, “The Andes Popped Up by Losing Their Deep-Seated Rocky Load,” Science, no. 5881, p. 1275, DOI: 10.1126/science.320.5881.1275a.

What is the take-home lesson of this article?  That scientists recognized their past sins of omission and have now come clean?  That science is progressing toward a true understanding of the history of the earth?  If so, we have a piece of Jurassic mantle on the auction block.
    Geological models like this are a hopeless hodgepodge of assumption, presumption, paradigm, social pressure, tradition, arbitrary classification and motivation, mixed in with a little bit of data as seasoning.  Step back and look at how geologists do this kind of work.  Is it reasonable to think that some isotope ratios in groundwater, or some measurements of volcanic gases, are going to tell you what happened 40 million years ago hundreds of kilometers below a mountain chain, where no human could ever go, to a time in the past no human has ever seen?  Will a model on a computer, with inputs from field work mixed in with assumptions, provide a reliable account of processes at work in a massive mountain range spanning the length of a continent over millions of years? (see 02/05/2008 about climate models).  How could they ever know?  There is no possible way to rerun the millions of years to find out.  How could they be sure the model does not omit one or more crucial parameters that might dramatically alter the conclusions?
    If you still trust the geologists’ story, consider that these scientists just upset their predecessors’ apple cart.  They said it had “long been thought” that the Andes rose up gradually.  Now we are supposed to “know” that was wrong, and we should accept the pop-up theory.  What assurance does anyone have that someone a decade from now will not overturn this paper?  It happens.  In the years of reporting at this site, for instance, we have seen geologists change their story dramatically about the Grand Canyon.  In 2000, geologists were considering it might be less than a million years old.  That was a drastic change from earlier estimates, carved into National Park signs as The Truth, that the canyon was 70 million years old.  Later, The Truth was down to 5 million years.  Now, in the last few months, they have been revising the date upward again; first to 17 million, now to 55 million or more (03/05/2008, 04/10/2008).  Reality has been buried in these conceptual sediments.  The only clue visible to a casual observer is that, when it comes to the true history of the earth, geologists are clueless.
    Understand the difference between observational geology and historical geology.  If a geologist can help Exxon find oil, or help you decide if your property is stable enough to build a house on, that’s great.  Thank goodness there are people trained in the observational skills and mechanics of rocks and soils and minerals to figure these things out.  There are quite a few geological skills one can learn in the university that are very useful.  We can watch geological processes, like volcanoes and earthquakes and floods, and make reasonable inferences from them about how certain formations came about.  Some processes can be studied with experiments in flumes and shake tables.  Even then, however, nature surprises us.  The eruption of Mt. St. Helens overthrew several major assumptions about the speed and power of geological processes.  A flume experiment recently challenged a long belief about how mudstones form (see 12/14/2007).  We can’t even be sure of things we can see in real time; how much less about processes in past mythical millions of years?
    To the extent geology can help us organize our experience, and give us a measure of explanation, prediction, and control, it is useful.  Notice the operative word is “useful,” not true.  Historical geology, though, is wedded to belief systems about an unseen past.  It is useless except, perhaps, as entertainment.  Its belief systems are not derived from science.  They are imposed on science.  Historian of geology Martin Rudwick said,

Even at the opening of its “heroic age” [ca. 1790-1830], geology was recognized as belonging to an altogether new kind of science, which posed problems of a kind that had never arisen before.  It was the first science to be concerned with the reconstruction of the past development of the natural world, rather than the description and analysis of its present condition.  The tools of the other sciences were therefore inadequate.  The processes that shaped the world in the past were beyond either experiment or simple observation.  Observation revealed only their end-products; experimental results would only be applied to them analogically.  Somehow the past had to be interpreted in terms of the present.  The main conceptual tool in that task was, and is, the principle of uniformity.
—Martin J.S. Rudwick, “The Principle of Uniformity,” History of Science, vol. 1 (1962), p.82; cited by Terry Mortensen, Ph.D., The Great Turning Point (Master Books, 2004), p. 229.

From philosopher and scientist William Whewell in 1840 to David Raup in 1983, observers have pointed out that geology is a different kind of science.  It cannot test and repeat things like you can with pendulums and space flight.  Historical geology is profoundly theory-laden.  Data are interpreted according to popular models and prevailing ideas.  Rare is the maverick willing to think outside the box.
    Mortensen documents in his book that Lyell and other 19th-century geologists effectively commandeered and institutionalized a certain approach to geology, uniformitarianism, that has ever since been beating its head against contrary evidence (05/22/2003, 03/31/2007).  The millions-of-years mentality has become uncritically-accepted dogma.  The standard geological column has been ensconced as a monument to Lyell and Hutton, like the temples of the ancient Greeks (read the telling quotes by Stephen J. Gould and Derek Ager in an article by CSM in England, Lyell’s country).  Long ages and uniform processes are accepted before the data are even examined.  Geologists are not discovering these vast expanses of time.  They are making measurements in the present, and offering them as votive sacrifices to the paradigm.  Historical geologists may make modifications to the temple, add new rooms and change the artwork, but it would take a religious conversion to make them change temples.