The green planet-killer.

Forget asteroids or nuclear war. Science Daily now has me worried that we’re all going to die from toxic pond scum:

The microscopic plants 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.

James Castle and John Rodgers of Clemson University think the same thing happened during the five largest mass extinctions in Earth’s history. Each time a large die off occurred, they found a spike in the number of fossil algae mats called stromatolites strewn around the planet.

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.

Of course, as winters get warmer, the stuff has been creeping further north every year.