1. For the soil profiles below, label the horizons (A. B, C, or R) in each of the soil profiles using the spaces provided next to each image. For this activity there is no 0 Horizon visible. Profile A Profle B Profile C 2. At the base of each profile above, number the profiles according to the proper sequence of development. Remember that the oldest is what happened first! I 3. Approximately how many years would it take for one centimeter of topsoil to develop? 3. Approximately how many years would it take for one centimeter of topsoil to develop? 4. What causes soil erosion? 5. Which layer of a soil profile forms first from the bedrock? 6. Which layer in a soil profile contains the most organic material. and why? 7. Why would certain environments not produce or have an O Horizon?