Probably the most useful science that encompasses every other science, math, and engineering. Without it the water you drink would kill you or not be there (groundwater aquifers), the buildings we use would subside/crack/soil compress/liquefy/corrode/fail, just about anything wouldn't exist (what do you think steal, iron, copper, titanium, etc. are mined from?), there wouldn't be oil, natural gas, or coal (the world would stop), we would still think the Earth was 6000 years old, the environment would die, and a bunch of other things you wouldn't even think of would cease.
If you don't know what geology is, you are an absolute idiot.
by Bill_Nye April 30, 2010