A view of a phytoplankton bloom near Alaska's Pribilof Islands. The milky green and light blue shading of the water indicates the presence of vast populations of microscopic phytoplankton. NASA hide caption

itoggle caption NASA

Volunteer Tom Strain carries debris from an empty lot as part of an Earth Day cleanup effort in Camden, N.J. The Earth Day events celebrated on April 22 promote a sustainable and clean environment. Mel Evans/AP hide caption

itoggle caption Mel Evans/AP