A really great man. I don't know much about Gaia but I've used his electron capture detector in a small portable gas chromatograph that our company developed. We could detect SF6 at concentrations of one part in a thousand million and the detector could probably work at much lower ones.
Didn't he invent the electrically heated motorcycle suit too? I could be wrong.
I've always tended to think of him more as a philosopher than a scientist, but there you go.