Best Online Reference Resources, Earth Studies:

• National Academies, Space Studies Board, Earth Studies Committee
  
  
• NASA's Earth Observing System - Huge source of data and images
  
  
• Earth Studies at Jet Propulsion Laboratory - Good links and overview
  
  
• Extensive lists of online resources in Earth Studies from "Integrating the Internet"
  
  
• Mt Holyoke Earth Studies - Resource Links