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Doubting the Proof of the Ice Ages . The pre-publication typescript of the paper that proved the astronomical theory of the ice ages - headed 'Manuscript accepted for publication by Science (as submitted Oct. 12, 1976)' - and the working copy of Stephen Jay Gould, who read it with a sceptic's pencil and did not believe it. Hays, Imbrie and Shackleton demonstrated here, from two deep-sea sediment cores, that the rhythm of the Pleistocene glaciations over the past half-million years matches the slow variations in the geometry of the Earth's orbit - the eccentricity, obliquity and precession cycles calculated by Milutin Milanković - and so revived and confirmed a theory that most geologists had abandoned. Gould, then a Harvard palaeontologist whose own work on Pleistocene land snails tracked exactly these glacial cycles, worked through the typescript in dense pencil annotation on its title page, dissecting the argument into its own four steps and concluding that the orbital signal was 'just an effect for Milank[ovitch]'s, not claims' - that what looks good in direction is, in his own summary phrase, 'a major problem in magnitude (my point).' The copy is unsigned but carries his filing mark and his hand; his verdict lands, as it happens, precisely on the weakness the authors themselves confessed. The provenance rests on the boxed filing mark 'H5' at the head of the title page, which matches Gould's practice elsewhere, together with the pencil hand of the annotations; the document is not signed. What the hand records is a working analysis rather than a formal review: the typescript is a copy of the manuscript already accepted by Science, reproduced and circulated after the editorial decision was taken, and Gould has taken it apart for his own purposes, as an outside reader thinking on paper. The distinction matters, because it fixes what the object is - not a referee's verdict solicited by the journal, but the private reckoning of a working scientist with a result he found important and could not accept. Under a heading he set down as 'My approach' he numbers the paper's logic in four movements. First, the data: the two cores, the oxygen-isotope record in the foraminifer Globigerina bulloides, the summer sea-surface temperatures reconstructed from radiolarian assemblages, and the puzzling abundance of the radiolarian Cycladophora davisiana, beside which he pauses to work out for himself what the species signifies - 'not clear what [it] means, but lots today' where the summer surface is of low salinity and cold water lies beneath, near the Antarctic and its summer melt. Second, the prediction: the twenty-one-thousand-year precession and forty-one-thousand-year tilt cycles, and the sharp question 'why just ecc[entricity]', with a note on the tenth-of-a-percent insolation difference and a reference to 'Broecker's curve'. Third, the raw curves and their calibration, where the assumption of constant accumulation rates and the radiocarbon anchoring draw the flat marginal verdict '120,000 correlation (problem)'. And fourth, the results, where he sets the paper's own variance figures against one another - twenty-three-thousand years at ten percent, forty-two-thousand at twenty-five, 'but 50% ? 100,000' - and writes 'OK but not match prediction of 1 to 1 response.' The objection is exact. The dominant hundred-thousand-year cycle of climate corresponds to eccentricity, which is by far the feeblest of the three orbital forcings, and the effect is far larger than any linear, one-to-one response to that forcing could produce. It is a problem of magnitude, not of direction, and it is the one weakness Hays, Imbrie and Shackleton had themselves confessed, in a section of their paper headed 'The 100,000-year cycle.' A lesser reader might have missed it under the weight of the result; Gould went straight to it. Gould had good contemporary reason to care, and it was not the reason a later reader might assume. Through the late 1960s and 1970s h.
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