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。
2
The U.S. Geological Survey (USGS) maintains an online database of fly ash-baseduranium content for sites across the U.S..
美国地质调查局(usgs)拥有一个全美浮尘铀含量的在线数据库。
3
Based on the above situation, the author proposes some corresponding Suggestions for uranium prospecting and exploration in China in the future.