A geologist is studying a new soil profile. In analyzing the profile, she finds that the topsoil is rich in organic material. She concludes that this soil would be great for growing crops.

What materials combined to form the topsoil?

1. weathered bedrock and wind-blown sand
2. decomposed humus and wind-blown sand
3. decomposed plant litter and weathered parent material
4. deposited sediment and decomposed plant litter