Plants produce oxygen as a by-product of photosynthesis, but most plants cannot live in anoxic soils. Anoxic soils form when soils gets compacted and you lose the space between the soil particles. Why can't most plants live in such anoxic conditions? (hint: look at the structure of the cell from the pre-lab)

weathering - colorado river carves land in arizona to form the grand canyon. cracks form in a sandstone wall surrounding a house. a marble statue near the science museum is changing color due to rainfall

erosion - after a rainstorm, soil and rock piees litter the roadways. the sand dunes in the sahara desert are changing shape.

here's your answer.