Discuss the top 3 most important things that you have learned about Earth's Physical Geography through this course. Be sure to explain, specifically, why you think each of the topics you select is of particular importance in helping us understand the geography of the world in which we live. In addition, you should discuss the extent to which any of the topics you select pertain to the "Twelve Key Issues for the 21st Century" that are presented in Ch. 17 of Elemental Geosystems 7th Ed.