Topsoil comes in many different forms, from nutrient-rich dirt to desert sand.
Can the Mississippi River change direction?
If salts are constantly washing into rivers, lakes and oceans, why aren't inland lakes salty as well?
River deltas are coastal valleys where rivers empty into the sea. Standing on a river delta you don't expect the ground beneath your feet to be disappearing.
Why do mountains stop growing? Find out on this Moment of Science.
In the desert, the absence of water means little or no chemical weathering can take place. Instead, erosion, frost, sedimentation, and the huge temperature fluctuations between day and night break down the rocky surface into sand or gravel.
Kimberly Sessions, of Atlanta, Georgia wrote to A Moment of Science with the following question: “I know why the ocean is still salty: evaporated water leaves the salt behind. But how did it get salty in the first place?”