One of my roles at the University I'm currently teaching at is that of lab/discussion instructor for a Calculus-based 2nd semester Physics class. It's a small department (without a separate earth sci/geo dept), but the people are great to work with. Plus, I get to learn and review a whole bunch of physics that I've spent the last few years forgetting as I worked on my dissertation.
Science is fun for the mind. Geology draws on biology, chemistry, physics, math - it is the ultimate applied science. So how does a sedimentologist/paleontologist teach physics? The first part is easy - I have the answers and solutions beforehand. The second part is harder, but much more important. I can't just hand out a problem set or lab activity and then disappear, waiting for them to hand in their work. I have to answer their questions about the activity. Which means I have to understand the problem set at a level beyond just the answer. I have to be able to identify whether the students' thought process will lead them to a proper solution - and help extract them from an untenable solution attempt, no matter what mess they may have gotten themselves into. Ultimately, I have to understand how to solve the problem, but I also have to understand how an undergraduate views and may attempt to solve the problem.
Plus, when we (as geologists) draw a geologic cross section, or a sedimentary particle falling through a column of water, we are constructing a physical model of how the world works. The skills required for successful analysis and problem-solving in physics are similar to those of all branches of science: identify the desired outcome, lay out the steps required to reach a solution (including formulae, quantitative estimations, etc.), solve the problem, check the calculated/estimated answer to what may be reasonably expected (and revise/retry if necessary). It's good exercise for the scientific mindset.