Two provocative ways to see long-term changes on earth are currently being promoted in honor of Earth Week . A Web site by NASA, and an app from HarperCollins, both show striking side-by-side satellite images of locations that have changed dramatically over time spans of up to 30 years or more. The primary intent is to show how we humans are altering the planet s surface.
NASA has posted more than 160 comparative views on a Web site it calls State of Flux . The sharp images are grouped into categories, such as human impact (see below).
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