1. processes initiated by people that shape earth's surface and interact with plant and animal life to create, sustain, and modify ecosystems physical systems
2. activities occurring in nature that shape the earth's surface
human systems
3. processes occurring in nature that shape the earth's surface and interact with plant and animal life to create, sustain, and modify ecosystems
physical processes
4. physical and human processes that shape the earth's surface and interact with plant and animal life to create, sustain, and modify ecosystems
systems