story identification - Book about ancient Martian astronauts being the root of modern humanity and time travel

If I recall it correctly, this book has two main characters, both male, one of them big and well muscled. During the novel, they found evidence that the current human race descends from ancient Martian astronauts who traveled to Earth in prehistory, causing the extinction of prehistoric Earth humans, (which explains the Missing Link in human evolution).

Later in the novel the big guy travels back in time (no idea of how or why) to Prehistory.

And near the end of the book, the other main character, during an archaeological field research, finds remains of a human being who lived thousand of years ago, a human with large bones, and who holds an item that could not be made in that era (a gold plaque? A metal rod?)

That's all I can remember. I know it is not from the ABC, Asimov, Bradbury or Clarke.

Thanks in advance.

Answer

To clarify the OP description of the book Inherit the Stars by James Hogan: There are two main scientist characters who get called in when a 50000 year old human corpse in a spacesuit is found on the Moon. This corpse, called Charlie, has a diary that they start to interpret. This gives them lots of info about Charlie's life and times.

Charlie has a buddy, Koriel, who goes with him in his wartime adventures on the moon. He's the well-muscled fellow. It turns out the Moon used to orbit a different planet, in the current Asteroid belt, not Mars. That's where Charlie is from. Koriel was leading a group of survivors of the war across the Moon when Charlie died.

At the very end a different research team finds Koriel's body, on Earth with dogtags, which they throw away since no 50000 year old human would have such a thing.