Well - I know you're just citing these two things as examples of things that COULD have occured, but to address them specifically (which is not to say that OTHER things couldn't affect the dating process...):
- Scientists, somehow (I've never really researched it), have determined (with a certain accepted margin of error) the state of the ozone layer in the past. In all honesty, though, the ozone layer is only one small part of our atmosphere and not the primary source for the shielding of proton radiation. If it has grown or shrunk in the past is a given - it's affect on the formation of Carbon-14 in the atmosphere is probably less of a "known quantity" but there are much greater minds than mine sorting that one out, I'm sure.
- Geologists have a very solid knowledge of the state of the Earth's tectonic plates a million years ago. There is only so much mass that comprises our planet - and for the entire surface of the planet to be raised 6 miles would be a huge increase in the requisite mass that would certainly have been determined by the scientists who study this.
If I were looking for things that would skew Carbon dating, I would look for events such as asteroid collisions, nearby volcanic eruptions, earthquakes, etc that are "statistical long shots" and could have contaminated samples thousands/tens of thousands of years ago and not be known by our scientists.
Who knows - something like that could have happened to create such an ancient reading on this particular fossil.