Earth science
The Encyclopedia of Earth has an online “course’ in Environmental Science — although I would call it more a textbook, since it appears to merely consist of pages of text, rather than including anything interactive.
Earth Sciences and Geography http://webs.cmich.edu/resgi/
How volcanoes work describes the science behind volcanoes and volcanic processes. It is sponsored by NASA and is intended for university students of geology and vulcanology and teachers of earth science.
http://sci.sdsu.edu/how_volcanoes_work/
Carleton College offers resources for those teaching college students about the geosciences http://serc.carleton.edu/teachearth/index.html
Geology.com has geology and earth science news and information
The Digital Atlas of Ancient Life, a free app developed at the University of Kansas, enables anyone with an iPhone or iPad to discover and classify fossils. The app links to pictures, maps and information about how long ago fossils occurred, to help people identify fossils if they find them, and focuses on fossils with origins in the Pennsylvanian period, about 290 million years ago, with fossils common to Kansas and the Midwest; the Ordovician period, with fossils often found near Ohio; and the Neogene period, with fossils usually located the Southeastern U.S.