Stopwatch for Magnetic Reversals

An article in the current Nature reports that reversals of the Earth's magnetic field appear to take an average of 7,000 years to happen, at least judging from the last four reversals. This is little news—the data set is very small—but it's a good example of mining data produced for other purposes. The new dates come from high-resolution seafloor cores taken during the Ocean Drilling Program. And it helps clarify the answer to another popular question: what happens to migrating animals during reversals?