The archaeological evidence, slender as it is, on King David and Goliath

http://www.bbc.co.uk/dna/h2g2/A9914268

It is interesting to note that the Moabite Stone
contains the earliest known extra-Biblical
occurrence of the tetragrammaton, according
to the article.

But, I ask how scientists know that it dates to
the 9th cent BC.

d.c.
.