200多万年前的马蹄蟹化石,与今天的马蹄蟹几乎完全相同:它们是三叶虫最近的亲戚。
Horseshoe crab fossils over 200 million years old are almost identical to contemporary animals: They are the closest living relatives of the trilobites.
大部分在古生代岩层中发现的化石都是没有脊骨的无脊椎动物,例如珊瑚、软体动物和三叶虫。
Most of the fossils seen in Paleozoic rocks are invertebrate animals lacking backbones, such as corals, mollusks and trilobites.
冰河时期海洋中多空虫贝壳化石中积聚的较重的氧同位素比较多,而另一种轻的氧同位素则更多地积聚在古代冰层和积雪中。
During glacial periods, the forams' shells contain more of the heavier of two oxygen isotopes, as the lighter one is preferentially accumulated in snow and ice rather than the ocean.
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