Mass Extinction by Gases


These days, be it in politics or science, things seem to accelerate at a speed that occasionally makes us wonder what we really know. Or if we know anything, for that matter... a humbling thought.

Take the dinosaurs, for example. We all know from biology class that they got wiped out due to an asteroid impact and the subsequent ecosystem disaster that spanned the globe. Right?

Maybe not. Recent scientific findings suggest the cause of the demise of the giants that roamed the Earth 65 million years ago might be a different one than previously thought.

Even though the asteroid-collision, swift-death theory is still popular among scientists, in the last few years researchers found that some of the data didn't add up.

New fossil analyses indicated that at least two of the "Big Five" extinction periods were drawn-out processes extending over hundreds of thousands of years, rather than a single, catastrophic strike from outer space.

In a September 2006 article, Scientific American stated that "A new type of evidence reveals that the earth itself can, and probably did, exterminate its own inhabitants."

And it might have done that via the world's oceans, or rather, sulfurous gases rising from the ocean floors.

Scientists have known for a long time that the oxygen level in the air around the time of the mass extinctions was much lower than it is today, but the reason was - until recently - undetermined. Some assumed it might have been due to large-scale volcanic activity, which could have raised CO2 levels in the atmosphere, reducing oxygen and leading to extreme global warming.

But volcano eruptions never sufficiently explained the large die-off of marine life or, for that matter, plant death on land, because plants should theoretically thrive on increased CO2 levels.

Reanalyzed data from the mass extinctions has now revealed the presence of tiny photosynthetic green sulfur bacteria - microbes that live in anoxic, i.e., low-oxygen, conditions such as the depths of stagnant lakes and the Black Sea.

"Those deep-dwelling anaerobic microbes," explains Scientific American, "churn out copious amounts of hydrogen sulfide [H2S], which also dissolves into the seawater. As its concentration builds, the H2S diffuses upward, where it encounters oxygen diffusing downward."

For a while, the oxygenated and hydrogen sulfide-saturated waters stay separated and their interface, called the chemocline, is stable. But if that fragile balance is disturbed, things can get bad fast.

Calculations by geoscientists Lee Kump and Michael Arthur of Pennsylvania State University have shown that "if oxygen levels drop in the oceans, conditions begin to favor the deep-sea anaerobic bacteria, which proliferate and produce greater amounts of hydrogen sulfide."

If the level of H2S were to increase beyond a critical threshold, "the chemocline separating the H2S-rich deepwater from oxygenated surface water could have floated up to the top abruptly. The horrific result would be great bubbles of toxic H2S gas erupting into the atmosphere."

And if enough of this poison had been produced - which the studies indicate it had - it might well have led to extinctions both on land and in the sea.

According to Kump and Arthur's estimates, "the amount of H2S gas entering the late Permian atmosphere from the oceans was more than 2,000 times the small amount given off by volcanoes today. Enough of the toxic gas would have permeated the atmosphere to have killed both plants and animals - particularly because the lethality of H2S increases with temperature."

The authors say that volcanic eruptions would have played a role as well, blowing vast amounts of CO2 and methane into the atmosphere and causing rapid global warming that encouraged further growth of the deadly bacteria.

"But the most critical factor seems to have been the oceans. [...] Oxygen-breathing ocean life would have been hit first and hardest, whereas the photosynthetic green and purple H2S-consuming bacteria would have been able to thrive at the surface of the anoxic ocean. As the H2S gas choked creatures on land and eroded the planet's protective shield, virtually no form of life on the earth was safe."

Could something like this happen again, wiping out most of the world's species including humans?

Some scientists think we could again see conditions favoring the build-up of hydrogen sulfide gas in just 200 years.

"The so-called thermal extinction at the end of the Paleocene began when atmospheric CO2 was just under 1,000 parts per million (ppm). At the end of the Triassic, CO2 was just above 1,000 ppm. Today with CO2 around 385 ppm, it seems we are still safe. But with atmospheric carbon climbing at an annual rate of 2 ppm and expected to accelerate to 3 ppm, levels could approach 900 ppm by the end of the next century, and conditions that bring about the beginnings of ocean anoxia may be in place."

Does that mean mankind will go extinct around the year 2300 - and doesn't it mean the Global Warming doomsayers have been right all along?

Even though we're far from having all the answers, we recommend taking this information with a grain of salt. First of all, Kump and Arthur's findings are still a hypothesis, not a fact. Second, even though the existence of global warming is now accepted by many in the scientific community, there are serious and credible countervailing views and it is far from proven that man-made emissions, rather than natural causes, are the likely culprits. And third, we would think that in two hundred years, humans may have found technologies to deal with the looming threat, if there actually is one.

But we found the theory interesting, which is why we brought it to your attention here.

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Posted 08-07-2007 10:59 PM by Shannara Johnson
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