The words “less” and “fewer” cause problems for some people. I wrote a post about that problem recently. The gist is that when you’re counting something, use “fewer,” and when you’re measuring, use “less.” If you’re not comparing, the words are “number” and “amount.” Here’s an article with a tricky usage:
Deep ocean sediment cores from this period also indicate no changes in glacial activity, based on the amount of oxygen isotopes in the cores.
Isotopes are discrete things that you can count, right? Oxygen has about a dozen of them, from 12O to 24O, (mainly 16O) and molecules and atoms are discrete things, too, right? Why is this sentence correct? Because the authors (whom I believe areAssociate Professor of geophysics, University of Leeds, and Associate Professor of Geophysics, University of Leeds) are measuring the size of the collection of these isotopes as if they were a mass, not individual atoms. If the authors wanted to point out that they were distinguishing among the isotopes, they could say “amounts of isotopes.”
Lesson: be alert to what you are saying when you write. These guys did it right.