I recently attended the AGU conference in San Francisco. As you might imagine, there was much excitement there about Google Earth and KML. I heard from a large number of scientists who are using these tools to present geological information to the public at large.
The advantage of Google Earth is that it can show information that is otherwise dry and academic in ways that are visually fascinating. Large databases of geological data can be transformed into 3D presentations that capture the imaginations of the rest of us. Scientists are also drawn to these tools because Google Earth and Maps are used by many millions of people worldwide and thus provide a huge audience for the stories these scientists want to convey.
Compelling examples of such geological and environmental implementations include:
Layers - These show a number of interesting points of interest around the world, such as volcanoes, glaciers, mountain ranges, water bodies and more. These layers include Smithsonian, National Geographic, UNEP and Geographic Features, among others.
Logging in Northern California - Rebecca More of the Google Earth team created this KML file that describes planned logging near Los Altos and how it could affect nearby communities. Read more about this on Google Earth Blog.
Glaciers - I also learned about this via Google Earth Blog. A poster on the Google Earth Community BBS created this KML file that shows condition of glaciers around the world.