A Walk Through Time

Fortune's Wheel

440 Million Years Ago

Global environmental change and continental glaciation induce a mass extinction which affects all marine animals. As the Ordovician period closes, over 50% of species worldwide decline and then vanish. The mass deaths open new niches for benthic (bottom-dwelling) and planktic (free-floating) marine life. New species and new groups of organisms which depend on these primary producers evolve. Researchers estimate biodiversity did not fully recover from this extinction for 25 million years.

Phytoplankton (photosynthesizing protoctists) bloom in colder, resource-rich waters. They, in turn, enrich the food web. It is a period of plenty in the seas: plenty of room and plenty to eat.

Computer and satellite technologies make visible the ubiquity and power of ocean phytoplankton. This composite, highlighting chlorophyll, shows ocean productivity. Note the blooms of life in colder waters. (Photograph courtesy NASA)

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