Just as radiocarbon dating gives the ages of once-living materials up to tens of thousands of years old, longer-lived radioisotopes are used to date rocks that are millions or billions of years old. Now, two wrenches have been thrown into the works. Joe Hiess and colleagues of the British Geological Survey have found that the ratio of uranium-238 to uranium-235 varies more than anyone previously thought it did, or could.1 The result has a small but significant effect on the widely used uranium–lead dating scheme. And a team of researchers led by Michael Paul (Hebrew University in Jerusalem) and Takashi Nakanishi (Kanazawa University, Japan) measured the half-life of samarium-146 to be 35% less than the currently accepted value.2 Samarium-146 dating is of more limited applicability, but if the new measurement is upheld, it means a major revision in all the dates derived from it.
Uranium’s two long-lived isotopes,...