Better still, it became apparent to him that one could use radioactivity as a clock, with the half-life of a decay series enabling us to calculate the age of a rock.
更妙的是，显然人们可以用放射性作为时钟，用衰变系列的半衰期计算出岩石的年龄。
2
That fall into the cave happened 1.977 million years ago, according to dating based on the rate of decay of uranium in the rock layer that holds the fossils.
根据保存这些化石的岩石层里铀衰变率的基础上所确定的年代，那次掉入洞穴事件发生在197.7万年前。
3
When the stress reaches a certain level, the accelerated creep damage of rock occurred after the decay creep and steady creep.