Speaking of out of time artifacts, I have this book that had some interesting pictures of some of them. A sparkplug like device was dated to be a few dozen million years old. Not only that, but human-like footprints were discovered as well. Some have turned out to be hoaxes, but many are still unexplained.
These ones were barefoot and huge. An early bigfoot?
But there was one I've always been interested in. A fossil of a shoeprint had been found, crushing a trilobite. (Ancient water bug thing) Perhaps an angry time traveller stuck in the past, taking it out on a poor trilobite?