Charles Q. Choi, LiveScience Contributor
The cosmic impact that ended the age of dinosaurs killed many living creatures on land and in the sea, but scientists have found, puzzlingly, that life in freshwater largely escaped this fate.
Now new research suggests freshwater life survived extinction because they were better adapted to withstand rapid changes in their surroundings, which helped them outlast the crises in the wake of the catastrophe.
The mass extinction event the scientists studied (also the most recent and most familiar) is known as the K-T event or, more recently, the K-Pg event. The disaster, which killed off at least 75 percent of all species on Earth, including all dinosaurs except for birds, was apparently triggered by acosmic impact that occurred in what is now Mexico about 65 million years ago. [Wipe Out: History's Most Mysterious Extinctions]
Past research suggested that while marine life was devastated by this mass extinction, freshwater organisms underwent relatively low extinction rates. Now investigators suggest the secret of their survival may have been all the variability experienced by freshwater life.
Water would have helped shelter life in rivers and lakes, as well as the seas and oceans, from the initial blast of heat from the cosmic impact. However, the giant extraterrestrial collision set fire to Earth's surface, darkening the sky with dust and ash that cooled the planet. The resulting "impact winter" and its lack of sunlight would have crippled both freshwater and marine food chains by killing off microscopic photosynthetic organisms known as phytoplankton that are at the base of the marine and freshwater food chains. ...more