Another book I abandoned. It was actually kind of promising, until the author hit me with something totally unbelievable.
In this case, about half way through, he has his protagonists discover that humans are not native to Earth but are extraterrestrials who have only been here about 40,000 years. With no other explanation at all. And the characters, an archaeologist and a geologist, just accept this with a "Oh so that is it." He even mentions that this makes us totally unrelated to all other life on Earth, but makes no attempt to justify it at all.
I mean, really. You might as well claim that everyone is made of plastic and nobody happened to notice. It's not even that you couldn't tell a story in which humans didn't evolve on Earth - but you need to at least address the fact!