Despite the common notion that the earth is in the sweet spot with respect to our distance from the sun, the truth is we're a little too far out. By the rights of simple thermal science, our planet should be locked in ice right now. And since our sun was even cooler in the past, the primeval earth should have quickly settled into a permanent, stable, snowball condition billions of years ago.
Fortunately, a class of microbes belonging to the archeae evolved early on1, and one of the branches that rose to prominence were methanogens: they ate hydrogen and carbon dioxide, and farted methane. By 3-4 billion years ago these tiny critters had spread so far and wide that their waste gas painted the ocean red and tinted the sky orange. Lucky for us, that waste methane held onto heat dearly, about 23 times more powerfully than CO2.
Lunar Dawn by Karen Wehrstein (Artist's tip jar), from the cover of Kosmos: You Are Here. A primeval earth dominated by microscopic methanogens might have looked something like this 3-4 billion years ago.
But about two and half billion years ago at the start of the Proterozoic Eon, another microbe was thriving that belched a poisonous reactive gas called oxygen. We humans tend to think highly of oxygen, but the release of it in large quantities by newly arrived blue-green alga literally gassed most methanogens and other early microbes to the verge of extinction. With the demise of the methanogens, the thick quilt of methane could not be not replenished, and was scrubbed out quickly.
One result of the 'oxygen holocaust' seems to have been a global ice age; a snow-white earth from poles to equator with a sky that changed from methane orange to arctic blue. If not for out-gassing and buildup of GHGs in the atmosphere from helpful volcanoes and hot vents, the earth might be encased in ice to this day. A similar global ice age likely occurred about 700 MYA during the Cryogenian Period. As you can see, methane, along with CO2 and other GHGs, played a major role in all those ancient events. But it was just getting 'warmed up.'
By about 250 MYA our planet's ecology had become superficially recognizable based on modern criteria. The land and water in the Permian teemed with somewhat familiar vertebrate grazers and meat eaters, surrounded by smaller arthropods, worms, and mollusks. But in proto-Siberia a titanic volcanic region formed spewing GHGs into the air. This event may have been responsible for raising global temperatures some 5-10 degrees F (5 C). The climate change and acid rain produced by the Siberian Traps was bad enough, thousands upon thousands of marine and terrestrial species perished, enormous rain forests were converted into searing deserts. But then that heat worked its way slowly into the frigid sea floors where large stores of methane existed in a stable solid, icy form, and the melting began. The temperature shot up another 5-10 degrees F. The two temp spikes bracket the greatest extinction event in the history of life on earth.
Left (Or top) courtesy of Karen Wehrstein: The approximate location of the Siberian Traps and a possible impact crater that may have occurred around the same time. Are the two related? Right: Extinction events by bar chart. The Permian Extinction is the tallest bar labeled "End P."
So what's any of this have to do with us? Well, those methane burping microbes didn't all go extinct. Some found refuge from the their arch enemy oxygen by making a living underground or in deep ocean sediments. There they went on happily producing methane, releasing it in dribs and drabs into the surrounding earth. But over the last eon or two, in some places the waste gas from those microbes was unable to escape and get recycled. There it has built up for all that time, trapped in the permafrost, in ocean beds, and under sheets of ice--until now.
One of the few survivors of the P-T extinction was this cynodont from about 225 MYA. Lucky for us, because this cute little egg-laying mammal-like reptile, or something similar, is the probable ancestor of all modern mammals: horses, dogs, whales, and so on, including of course, humans. Illustration courtesy of Carl Buell.
One of the tipping points in the intricate computer predictions of future global warming concerns that trapped methane. As ice sheets retreat, once frozen soil thaws, and methane ice melts, any trapped methane can now escape en masse. How much is there and how fast is it being released? Possibly quite a bit, according to the climatologists at Realclimate.
The consequences of this phenomenon are potentially dire. It's like throwing gasoline on to the global warming fire: It could herald a sudden, significant increase in global temperature, particularly amplified near the poles. Which means more melting ice and permafrost. leading to more methane release ... you get the idea. Massive sea level rises, more intense cyclonic storms, wildly swinging weather, acid rain ... The same kind of feedback process that may have contributed greatly to the Permian extinction.
So remember, as a pale blue flame of methane fries up your bacon and eggs this morning, or while you luxuriate in the hot shower before work: that colorless, odorless gas not only makes our lives easier, it helped bring life as we know it in to the world--and it can take it out as well.
Comments are closed on this story.