The movement of material due to differences in density is called?

The layers of earth are based on what two sets of characteristics?

At which boundary does subduction stop occurring, resulting in a mountain range?

Which of these is a drawback of using natural gas? a. it is fairly safe for use in homes.b. it burns more cleanly than crude oil products.c. scientists have developed new ways of extracting it.d. during its extraction, groundwater can be contaminated.