a long rock sequence that is older than half a billion years that is far less well defined in terms of fossils and less well preserved

红色部分为双重定语从句。其中that is older than half a billion years这个定语从句修饰的是 a long rock sequence这个名词词组，that is far less well defined in terms of fossils and less well preserved这个定语从句修饰的是a long rock sequence that is older than half a billion years这个名词词组。二个定语从句不在同一个层次上，所以中间不能使用并列连词。