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Extrapolating Beyond the Last Data Pointpublished Aug 19, 2009
In followup to our recent EOS paper "How Geoscientists Think and Learn" (Kastens, Manduca, et al, 2009), Michael D. Max, of Marine Desalination Systems, wrote:
I think this is an interesting point, that extrapolation beyond the last data point is more or less forbidden in science, but geologists do it anyway.
In recent years, though, society has been asking the geoscience community to answer questions about the future, rather than about the past: what will happen to the climate? when will the next earthquake be? etc. To think about the future, by definition, requires making interpretations outside the bounds of the available data, which as Dr. Max noted, is something that many scientists shy away from.
What do we need to do to teach the next generation of geoscientists to be (a) comfortable and (b) competent at thinking rigorously about the future?
Kastens, K. A., Manduca, C. A., Cervato, C., Frodeman, R., Goodwin, C., Liben, L. S., et al. (2009). How geoscientists think and learn. EOS, Transactions of the American Geophysical Union, 90(31), 265-266. (download requires AGU membership)
Extrapolating Beyond the Last Data Point --Discussion
[further thoughts from author of post]
Today I took a teacher's question about the early days of plate tectonics to my Lamont-Doherty colleague Walter Pitman, one of the pioneers of the use of seafloor magnetic anomalies for determining rates and directions of plate motion. He got to reminiscing about the paper in which he and colleagues put ages onto magnetic anomalies, shaking his head about how lucky they had been when they took 4 million years worth of magnetic reversals dated from land sections plus a handful of dated seafloor samples and extrapolated boldly out to 80 million years worth of seafloor magnetic anomaly record. Now there is a case of extrapolating beyond the last data point! The extrapolation worked because it wasn't just a blind extrapolation, it was an extrapolation based on a model, and the model, seafloor spreading, turned out to be correct.
In the same conversation, Walter passed on an interesting quote from former Barnard geology professor John Sanders, paraphrased: In sciences like physics and chemistry you are always trying to design an experiment to prove or disprove an hypothesis. In geology you are always trying to figure out what the experiment was.
Ref: Heirtzler, J. R., G. O. Dickson, E. M. Herron, W. C. Pitman III, and X. Le Pichon (1968), Marine Magnetic Anomalies, Geomagnetic Field Reversals, and Motions of the Ocean Floor and Continents, J. Geophys. Res., 73(6), 2119-2136. Online at: http://www.agu.org/pubs/crossref/1968/JB073i006p02119.shtml
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