No, there's no "hard evidence" in the article, but that's because when they start talking research methodology to reporters, the reporters' eyes
glaze over and they start babbling incoherently.
The gruop that did it is here:
www.msfat.com...
Done under a university grant and by university personnel, so they didn't wander out and chant mantras at the grass and get a "feel" for the date.
I suspect from the hints given that it's done by excavating layers of debris. They found the old Roman artifacts under the chalk (indicating it was
later than the Romans) and probably found other things as well (like more modern buttons or well-dateable artifacts. Then the chalk layer, then more
recent material.
However, the organization's contact info is on the website and you can ask them directly, I'm sure.
