It's way harder to get a Marine Biology degree at my school than it is Geology. You have to go to calc 2, orgo 2, and then you have semesters loaded with classes like comparative vertebrate A & P and animal development.

As far a science goes, in general there is less conceptual thinking involved in geology compared to the big 3. There are less huge developments, and generally less cutting edge research experiments. The GRE scores to enter the top PHD programs are less competitive than physics or biology.The nature of geology attracts the "outdoorsy" blue-collar type, who are usually scared away by physics and engineering because of theoretical knowledge required. All this comes together to make geology the whipping boy of intellectuals.

Edit: https://www.youtube.com/watch?v=sYMFHON8LFw