Algal Apocalypse
Another big problem for Earth could come from a tiny source, according to Caltech geobiologist Joe Kirschvink. He raises the possibility that diatoms — a type of microscopic algae that inhabit moist surfaces, lakes, rivers, oceans and soil — could alter Earth’s atmosphere in a fatal way.
These microbes live off fuel produced through photosynthesis, a process that converts light energy (photons) from the sun into energy a cell can use to function (sugar). As they photosynthesize, diatoms break up water into hydrogen and oxygen other organisms can then use to breathe.
But if mutant diatoms couldn’t use water — or other substances in their environment, like iron or hydrogen — they might be tempted to pick salt (sodium chloride) off Earth’s menu of molecules. These diatoms would release poisonous chlorine gas. Assuming the chlorine didn’t kill them and nothing else limited their growth, the diatoms would grow exponentially, setting off a death-by-inhalation doomsday.
“The damn thing could take the world over in a couple of million years,” Kirschvink said.
If his diatomical predictions pan out, it would be the second time biology issued a molecular death sentence for most living organisms on Earth. A similar scenario played out about 2.35 billion years ago when cyanobacteria, a type of blue-green bacteria, learned how to photosynthesize. The bacteria dumped oxygen molecules into the atmosphere — which until then was mostly carbon dioxide — and killed off species that couldn’t tolerate oxygen, Kirschvink says.
“Oxygen molecules at the time were unheard of in the environment,” he said. Once diatoms set in motion the “oxygen apocalypse,” there was no stopping them. They had an advantage over creatures that didn’t like oxygen.
Fortunately for Earth's inhabitants today, the water microbes need to photosynthesize abounds, so it’s unlikely they’ll set off a chlorine apocalypse any time soon, Kirschvink said.
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