Science: First the bedroom clock reassures you that you're right on schedule. Moments later, the kitchen clock tells you that you're running minutes behind. If you find that annoying, pity the geochronologists. For decades, two of their workhorse timepieces--isotopic clocks ticking to the steady decay of two different radioactive elements--have been disagreeing by millions of years.

Now geochronologists have recalibrated one of the clocks, bringing it into agreement with the other. They've tried it before, but this time it looks like the fix will stick. "This is a huge step forward," says geochronologist Mike Villeneuve of the Geological Survey of Canada in Ottawa. "You'd like to see it reproduced, but it looks very solid to me." The synchronization of clocks lends more support to a link between huge volcanic eruptions and mass extinctions.