I was reading Researchers Find New Information About 'Snowball Earth' Period, an article only a hopeless nerd like me would read casually on a Thursday afternoon, when I ran across an interesting quote. But first things first.
It is rather difficult to imagine, but approximately 635 million years ago, ice may have covered a vast portion of our planet in an event called "Snowball Earth."
According to the Snowball Earth hypothesis, the massive ice age that occurred before animal life appeared, when Earth's landmasses were most likely clustered near the equator, precipitated relatively rapid changes in atmospheric conditions and a subsequent greenhouse heat wave. This particular period of extensive glaciation and subsequent climate changes might have supplied the cataclysmic event that gave rise to modern levels of atmospheric oxygen, paving the way for the rise of animals and the diversification of life during the later Cambrian explosion.
This is obviously a subject of considerable interest if you are curious about the history of life on Earth. Specifically, these researchers want to figure out how Earth got out of the ice-bound state, an event which led to a rise in atmospheric oxygen levels, oxygenation of the oceans, and, eventually, rise of complex metazoans sometime thereafter.
But if ice covered Earth all the way to the tropics during what is known as the Marinoan glaciation, how did the planet spring back from the brink of an ice apocalypse?
... an article published on Feb. 5 in the Proceedings of the National Academy of Sciences, or PNAS, that provides new clues on the duration of what was a significant change in atmospheric conditions following the Marinoan glaciation.
"The story is to put a time limit on how fast our Earth system can recover from a total frozen state," Bao said. "It is about a unique and rapidly changing post-glacial world, but is also about the incredible resilience of life and life's remarkable ability to restore a new balance between atmosphere, hydrosphere and biosphere after a global glaciation."
I will spare you the details regarding proxy measurements indicating very high atmospheric CO2 levels after the planet-wide glaciation. Suffice it to say that a frozen planet prevented the very-long-term carbon cycle (of that time) from operating normally, which means that when volcanic outgassing spewed lots of CO2 into the atmosphere, that carbon dioxide remained there, eventually creating an enormous greenhouse effect which melted the ice, which further led to an explosion in cyanobacteria, primitive algae, and other protists, which resulted in a rise in oxygen levels. How long did the CO2 build-up take?
By using available radiometric dates from areas near layers of barite deposits, Bao's group has been able to come up with an estimate for the duration of what is now called the Marinoan Oxygen-17 Depletion, or MOSD, event. Bao's group estimates the MOSD duration at 0—1 million years.
[My note: the duration given in the research paper (linked-in above) is 0.208 ± 0.781 million years, or equivalently, 0-0.99 million years.]
"This is, so far, really the best estimate we could get from geological records, in line with previous models of how long an ultra-high carbon dioxide event could last before the carbon dioxide in the air would get drawn back into the oceans and sediments," Killingsworth said.
On the reasonable assumption that the CO2 build-up didn't occur very suddenly (0 years), the right answer is probably something like tens or hundreds of thousands of years.
And it here that we get this remarkable quote from Huiming Bao, Charles L. Jones Professor in Geology & Geophysics at LSU.
"To some extent, our findings demonstrate that whatever happens to Earth, she will recover, and recover at a rapid pace," Bao said. "Mother Earth lived and life carried on even in the most devastating situation. The only difference is the life composition afterwards. In other words, whatever humans do to the Earth, life will go on. The only uncertainty is whether humans will still remain part of the life composition."
Whatever humans do to the Earth, life will go on! That's encouraging.
Despite typical human hysteria about runaway greenhouse effects (à la Venus) and other Big Time Existential Threats which loom large in the unfettered human imagination, the humdrum truth is that humans can not wreck the planet, or utterly destroy its biosphere, and no cosmic is event is likely to do so either. The only important question, the "only uncertainty'" as Bao put it, after the humans have completed their evolutionarly "work" on this planet, is whether humans will still remain part of the life composition.
I'm betting not.