According to their site, the academy "is a not-for-profit with the goal of changing education for the better by providing a free world-class education to anyone anywhere. All of the site's resources are available to anyone. It doesn't matter if you are a student, teacher, home-schooler, principal, adult returning to the classroom after 20 years, or a friendly alien just trying to get a leg up in earthly biology. The Khan Academy's materials and resources are available to you completely free of charge."
CLICK HERE to view the list of Khan Academy tutorials available in the "Cosmology and Astronomy" category. . . Many of the tutorials are related to geology topics. (They really should have a "geology" category!) The tutorials may be helpful for students who want to review a topic. If you have a web site, you might post links to certain Khan videos that you think will be beneficial to your students. CLICK HERE to see how I have done this on my web site for students (scroll down once you get there).