The combined gas law allows you to derive any of the relationships needed by combining all of the changeable peices in the ideal gas law: namely pressure, temperature and volume
I'm not positive, but I believe it would be one near the Rocky Mountains.
Answer:
During ice ages, the most characteristic change to the planet has been the formation and spread large ice sheets and glaciers across much the Northern Hemisphere.
If you're looking for "what rocks are formed by changes..." it's Igneous Rocks.
