Contact the teacher of each course that you are considering to attend since different teachers have different opinions due to classroom-size constraints, etc. A few do approve of class auditing, where the only difference with enrolling would be that auditing does not result in a letter grade on your transcript.
Yes, if you are an environmental studies major, on the paleobiology track or an honors earth science major on the environmental science or geology tracks. In the spring semester of your junior year you must enroll in ENVS/GEOL399. In your senior year, you must enroll in ENVS/GEOL498 a and b. This two-semester senior thesis seminar prepares you for your thesis and facilitates its completion, as well as readies you for the steps you will take after graduation. If you choose to complete the environmental science or geology tracks in the earth science major without honors, a thesis is not required.
This website actually tells you everything that you need to know about EES courses.
The best way to get involved with ongoing research in the department is to take classes with professors whose research interests you, or talk to faculty in the department. They can point you towards professors or help you get their attention. Also, please see our Undergraduate Research page.
If you have questions about the majors, talk to the Assistant Director or the Undergraduate Chair, or visit our programs page where you can find descriptions of the majors, minors, and concentrations within each major. You may also want to talk with a MAP advisor. Once you're ready to declare, see your college/academic advisor. They'll make your worksheet "official". Once it is official, fill out a planner for your chosen major/minor and make an appointment with the Associate Director, Maria Antonia Andrews, to come in to declare.