Google Earth has exciting new features. Download the new version and explore underwater as you have explored land.
1. Google Ocean – the sea floor is now mapped, and data, pictures, videos, user-generated content are all now available (for example, you can check the the water temperature in the Florida Keys ( 71 F)). Here’s a video with Sylvia Earle exploring the new features.
Duke’s Pat Halpin contributed to Google Ocean and participated in the launch.
2. Sharing Tours to share content, you can create, narrate and share tours that others can open in Google Earth 5.0. The tour will run just as you recorded it, but it can be interrupted by the user to look around. It does not make a video, but is an easier way to share information. Here’s how, and even more help.
3. Historical information Google Earth has incorporated old images, like from San Francisco in the 1940s. Read about the historical imagery in Google’s Lat Long blog.
4. Google Mars Yes, you can explore Mars, too. 
Watch Frank Taylor explore Google Mars.
More information:
Google Earth blog video showcase
Google Earth blog descriptions of updates
Still not sure? Take a tour.