TAing one's entire way through grad school: possible or unlikely?

[InquilineKea]

Is it harder to do this in the geosciences than it is in other areas? Given that the geosciences have significantly lower student enrollments than fields like physics/math?

[Captain Crunch]

Not a problem, at all. Basically any reputable school with a decent offer will at least give you a 4 semester TA position. Some extend it beyond that if needed. Lots of schools allow geo 101 to fulfill a science gen ed, so there is big enrollment in 101 classes.