For years many scientists assumed that the multiple mass extinctions in the fossil record were the result of similar causes, most likely a meteorite or a similar cosmic catastrophes. However, a few years ago evidence began to come to light indicating that at least one major extinction - the "Great Dying" of the Permian era, 250 million years ago - probably took place over several thousand years or more, rather than a few decades.
After looking at alternatives, researchers arrived at the conclusion that this, and probably other mass extinctions, were caused by the emission of huge amounts of hydrogen sulfide into the ocean and the air. How? A blast of CO2 into the atmosphere (probably volcanic in origin) warmed up the planet. This in turn stopped ocean currents, allowing a type of hydrogen sulfide-creating bacteria to thrive. Stir well, wait a few years, and bad-a-boom-bada-bing, 90% of life on earth is dead. Cycle of life, right?
The bad news is that our own CO2 habits may be replicating the conditions that wiped out life forms a whole lot more long-lasting than us. Ward says he can imagine a time in 500 years when humans would have to wear gas masks to survive (not to mention animals, assuming there are still any around by then.) Sometime after that, even the masks wouldn't save us.
By the way, hydrogen sulfide is also responsible for the smell of rotten eggs and particularly foul flatulence, so before it killed us, it would stink up a storm. Think about that the next time you can't be bother to turn off the light when you leave the room.
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