求教 OG12 73

正确句子：Combining enormous physical strength with higher intelligence,the Neanderthals appear to have been equipped to face any obstacle the environment could put in their path,but their relatively sudden disappearance during the Paleolithic era indicates that an inability to adapt to some environmental change led to their extinction.

为什么这里不用appeared呢？以及为什么后面是indicates 但又是led。。。。。
不太清楚时态OTZ求解惑……