Algae have helped to sustain life on Earth since they first modified its atmosphere with photosynthetic by-products over two and a half billion years ago! From the microscopic to giant seaweeds, nearly 30,000 forms exist today. Algae made more recent forms of life on earth possible and have served mankind in many capacities. But some algae can turn “killer” when their growth explodes into massive algal blooms. Watch as researchers discover how algae can transform from life-supporting to life-threatening. Learn how we’ve depended on algae in the past and see the new ways we are putting them to use in cancer research, sewage and wastewater treatment, agriculture and household products. Includes teacher’s guide with curriculum applications, suggested teaching strategies, ideas for discussion and further study, glossary of terms, career opportunities and other reference information. 14 minutes.