For decades, scholars have debated whether the eruption of the Thera volcano in the Aegean more than 3,000 years ago brought about the mysterious collapse of Minoan civilization at the peak of its glory. The volcanic isle (whose remnants are known as Santorini) lay just 70 miles from Minoan Crete, so it seemed quite reasonable that its fury could have accounted for the fall of that celebrated people. This idea suffered a blow in 1987 when Danish scientists studying cores from the Greenland icecap reported evidence that Thera exploded in 1645 B.C., some 150 years before the usual date. That...