Just a couple of things to add to the mix. Am in the social sciences, just several steps ahead of you (about to start a PhD). Observations are of working in a local U.

1. Becoming an academic is a lifestyle choice. As someone mentioned earlier, you don't go into it to get rich. Some academics do become rich, but don't bank on it. What you do get is a significant amount of flexibility in managing your time, and the chance to ostensibly do something you love (though you may end up hating it as you plod through the PhD).

2. Every faculty has different hiring practices and terms. There's a general range, but there are numerous other factors which determine your pay.

3. IMO, you will be "underpaid" for the first 6 years of your career. Pay for postdoc, research fellows etc. is very low, compared to what you might be getting had you invested your intellect, time and effort in a job outside instead of spending 3-7 years pursuing your PhD.

4. To get tenure, you need to be on a tenure-track position. Many academic positions are not.

5. 6 years is how long the "tenure" clock is. You need to secure tenure within this time frame. The requirements vary from faculty to faculty. If you don't, there's a good chance you'll be let go by the university, unless you're really quite close to successfully submitting your portfolio for review.

6. During those 6 years, you'll be on a 3 year contracts (so 1 renewal).

7. Once you've got tenured, you're set for life. That's the pot of gold at the end of the rainbow. If you don't, well you'll have immense job security. Problematic if you've got commitments (family, financial, aging parents etc).