University of Illinois
University of Illinois: Illinois State Water Survey: Nitrogen Cycle: Human Impact on the Nitrogen Cycle
An overview of the impact of human activities on the environment and how those actions effect the nitrogen cycle.
Center for Educational Technologies
Exploring the Environment: Earth System Science
Explains what the four spheres of the Earth are, and the interactions between them.
University Corporation for Atmospheric Research
Ucar: Introduction to Climate
A detailed overview of the Earth's climate, with explanations about the difference between weather and climate, dendrochronology, palynology, and how Earth's climate has changed over time. All information is reinforced through pictures,...
University Corporation for Atmospheric Research
Ucar: The Water Cycle
This site provides a comprehensive introduction to the water cycle. Students construct a model to simulate parts of the water cycle. Includes background information, links to standards, lesson plans, and assessment ideas.
Encyclopedia of Earth
Encyclopedia of Earth: Physical Geography
Get a general grasp on the four spheres, five sub-fields, and two scales of physical geography.