Sentence:  ...And ocean salinity, of course, represented only the merest sliver of my ignorance. I didn't know what a proton was, didn't know a quark from a quasar, didn't know how geologists could look at a layer of rock on a canyon wall and tell you how old it was, didn't know anything, really. I became gripped by a quiet, <WSD>unwonted</WSD> but insistent urge to know a little more about these matters and to understand above all how people figured them out. 
Meaning of the word marked with <WSD> tags:  Not customary or habitual; unusual; infrequent; strange.