Glottochronology.

Glottochronology is beguiling, but ultimately, it's dangerous.
Everything I've read says the methodology is unsound. At best,
some broad educated guesses are being made in assembling the
figures. At worst, it's based on unsupportablely wild guesses.
It's like trying to externally calculate the velocity of a
moving object without calculus; until we get a Leibnitz/Newton
to give us such a calculus, any claims made by
glottochronology have to be taken with several
salt-mines-worth of salt.

Mark.