For clarification, a prerequisite is a course that must be taken before the course in question is started.
A corequisite is a course that should be taken concurrently with or before the course in question.

The Department of Earth System Science (ESS) actively checks prerequisites and corequisites. Before registering for classes, you should always check the current Course Catalogue to see if there are any prerequisites or corequisites for the courses you would like to enroll in.  In some instances, a pre/corequisite can be waived by consent of instructor. In most cases, the pre/corequisites are listed online in the schedule of classes. If you believe you have satisfied a prerequisite but are having difficulty registering, please contact the ESS department office.