I have found that one of the hardest things to do when I teach earth science is build background knowledge. One way to build background knowledge of geologic events is to use digital photographs. I found that many free images can be found on the web that allow student to see natural objects that they cannot be able to see firsthand.
Here are some resources that I used this year:
This website shows volcano photos from Earth and on other planets.
Erosion: How Sediment Moves
These websites show that rocks and sediment get moved from their original locations. They also show earth building up in some areas and other areas where there is sediment loss.
I found 2 websites with awesome fossil images.
Fossil Image Galleries from the Virtual Fossil Museum
I found that by using the images I found on these websites, my students were more engaged and their knowledge of earth science was enhanced.