How long will these footprints be on the Moon?
In a billion years, or even 5 billion years, these footprints will still be on the Moon. In that time Earth will undergo enormous changes due to plate tectonics but also to the processes of weathering and erosion that modify the landscape. Of course, if commercial flights to the Moon ever become a reality, the trash from new visitors could cover or erase the tracks left by the Apollo astronauts.
Earth materials weather by mechanical or chemical processes; mechanical processes change the size of a substance but not its composition and chemical processes change its composition. Different types of weathering can work together on the same material. Soil forms on top of rock, the type depending on the environmental conditions in the region. A soil profile exhibits horizons, the nature of which depend on the type of soil. Topsoil is extremely important since it is in good topsoil that crops can grow. Water, ice, wind, and gravity create or modify landforms on Earth's surface. These agents can erode or deposit features that indicate their presence. Coastlines are modified by waves and currents along shore; groundwater carves caves and deposits cave features; wind abrades features and deposits sands in dunes; glaciers carve mountains into characteristic features and deposits massive amounts of debris; and gravity causes mass wasting, such as landslides.