Toxin producing "killer" algae wiped off the dinosaurs, claims new study

According to US geologist James Castle, of Clemson University, South Carolina, fossil records indicate mass extinction but "they occurred more gradually than if caused solely by a catastrophic event."

Castle has an explanation. According to the geologist, blue-green algae, which produces poisons and depletes oxygen, was present in sufficient quantities to kill off many creatures on land or in the sea.

Ecotoxicologist John H. Rodgers has endorsed Castle's view and feels that current environmental conditions show significant similarity to times when previous mass extinctions occurred.

Both Castle and Rodgers have spent two years analysing data from ancient algal deposits - stromatolite structures - and have come to the conclusion that though climate changes, sea level, volcanic activity, even crashing asteroids, were primary causes of death of more than 50 percent of life on Earth yet they are all contributors while algae were the real "mass killers."

Algae are microscopic plants that usually exist in small concentrations, but a sudden warming in the water or an injection of dust or sediment from land can trigger a bloom that kills thousands of fish, poisons shellfish, or even humans.

The researchers, who analysed the five largest mass extinctions in Earth's history, claim that each time a large die off occurred, they found a spike in the number of fossil algae mats called stromatolites strewn around the planet.

"If you go through theories of mass extinctions, there are always some unanswered questions," Castle said. "For example, an impact - how does that cause species to go extinct? Is it climate change, dust in the atmosphere? It's probably not going to kill off all these species on its own."

But as the nutrient-rich fallout from the disaster lands in the water, it becomes food for algae. They explode in population, releasing chemicals that can act as anything from skin irritants to potent neurotoxins. Plants on land can pick up the compounds in their roots, and pass them on to herbivorous animals.

The researchers, who presented their theory at the annual meeting of the Geological Society of America in Portland, Oregon, have also raised concerns about how today's algae may damage the ecosystem in a warmer world.