Richard Treves is the author of kokae.com and blogs about the usability of Google Earth projects at Google Earth Design.
Recently, he created a very interesting timeline tutorial video that describes how to use the time slider in Google Earth. This particular post also provides a reasonable critique of this feature.
The time slider displays content in Google Earth along a sequence of time. Check out Frank Taylor's examples of time animations on gearthblog.com.
Learn more about using the time slider.