Earth science has to be one of my favorite things to learn about, so that means that we've spent a lot of time on it for school. I've had trouble teaching my boys about any other science topics. I try to move on to biology, but we always wander back to rocks and volcanoes. At least we had a garden one year. :)
Anyway, I think earth science is one of the easiest topics to teach because it's so easy to get out and experience it. But sometimes it's hard to know where to start. Since I grew up in the West, I know what's available in Idaho and surrounding states, so it's worked well for me.
I haven't found a lot of earth science books for younger children that I like though. We've had much better luck getting out of the house and doing earth science. I'm also not impressed with some experiments that are in earth science books. Baking soda and vinegar volcanoes just don't cut it here because a volcanic eruption is not a chemical reaction.
What I'd love to see if a series of books on each state co-written by an experienced homeschooling mother from each state, a geologist and a meteorologist. It would have experiments, but it would focus more on field trips, museums, and backyard science. It would be geared towards grammar stage, but it would be a useful supplement to How the Earth Works and How the Weather Works for logic stage.