Ten thousand years of treerings show that the carbon-14 level rises and falls about every 420 years.
一万年的树木年轮显示，碳14水平大约每420年上升和下降一次。
2
Replacement can be a marvelously precise process, so that details of shell ornamentation, treerings in wood, and delicate structures in bone are accurately preserved.
替换可能是一个令人惊叹的精确过程，因此贝壳纹饰的细节，树木的年轮和骨的微妙结构都被准确地保存。
3
For the time before records began, we have only "proxy records" reconstructed largely from treerings and ice cores, supplemented by a few incomplete written accounts.