- The first animals to ever set foot on land were the arthropods.
率先踏上陆地的动物是节肢动物 - Relatives of the trilobites,
它们是三叶虫的亲戚 - their hard exoskeletons had served as useful armor underwater.
坚硬的外骨骼在水下是有用的护甲 - On land, that armor supported them
在陆地上 这护甲支撑着它们 - and prevented them from drying out.
并防止水分流失 - They could also breathe through this tough exterior.
它们也可以通过这坚硬的外壳呼吸 - And with oxygen levels 60% higher than they are today,
当时的氧气水平比今天高60%