Inherit the Stars, by James P. Hogan

James P. Hogan's 1977 novel Inherit the Stars has one of the great set-ups in sci-fi.  Human explorers on the moon uncover an unusual find: a human in a space suit.  Clearly he's been dead a while, but no group of humans will own up to a missing crew member.  Soon researchers get the most shocking news of all: the corpse is 50,000 years old!  This discovery and subsequent related discoveries spark an investigation into the very origins of human life.

Upon reflection, one interesting thing about Inherit the Stars is that despite its being science-heavy, with lots of conversations between scientists comparing theories, it's very readable.  Also, with much of the text being made up these conversation among scientists, there's not a lot that actually happens, yet it's a fun and entertaining read.  And although it was first published more than 40 years ago, Hogan's anticipation of technological developments (and the fact that tech is not central to the story) has kept the story fresh.

Inherit the Stars, Hogan's first novel, established him as a reliably entertaining writer of hard science fiction.  This is definitely a novel that is worth revisiting.