Depends on the school. Even in the same discipline (I'm also in the geosciences like jofer) some departments don't accept grad students as MS students except in

Depends on the school. Even in the same discipline (I'm also in the geosciences like jofer) some departments don't accept grad students as MS students except in certain circumstances, such as U. Michigan, my current employer. Most of the grad students here come in with a BS and consequently (and understandably) take a little more time and often flail a bit more at first, relative to PhD students who start with a MS. Some schools that only/mostly take PhD students on give you a MS when you've written your first paper or taken you PhD qualifying exams. I did a MS before I did my PhD, at different schools and with reasonably different projects, and am glad I did. Where I did my PhD, it was difficult to be accepted into teh PhD program without an MS. However, I wouldn't say that the MS or equivalent is necessary to reach a 'full time course' because the American BS is less specialized than an equivalent degree elsewhere in the world, based on what I've learned from the many non-Americans I've worked with. edit to answer question better: In the American system, there is a lot of unrelated coursework (which has some guidelines, it's not just a sum of credits), but there are also a fair amount of core/science courses. I just looked at my coursework list and counted 16 courses (including fieldtrips and independent studies but not labs) in geoscience, then there is the requisite math, physics, chemistry. The American system still takes the idea of a well-rounded 'liberal arts' education seriously (feel free to be skeptical and call it welfare for poets and historians, although I don't entirely share this position). I think university in many countries is a shorter process, although their high schools may be much better...