NASA Worldview is a free online visualization tool that is a great launchpad for learners who are new (or veteran) users of satellite data.

The Earth System Satellite Images help students observe and analyze global Earth and environmental data, understand the relationship among different environmental variables, and explore how the data change seasonally and over longer timescales.  

What is the hydrosphere and why is it important?

Explore the biosphere and why it is important.