Global Warming Killed the Dinosaurs?

Since 1980, it has been widely assumed and accepted that prehistoric extinctions, and most significantly the famous dinosaur-killing extinction 65 million years ago, were caused by an asteroid colliding with earth, and rendering earth inhabitable. A large crater found on the Yucatan Peninsula of Mexico swept aside any lingering doubts about that theory. But while the dinosaur extinction could now be attributed to an asteroid collision, what about the other mass extinctions?

Scientists say that five different times in the earth's history, most of the world's life forms have simply ceased to exist.
The biggest extinction of them all was allegedly 251 million years ago, and wiped out 90 percent of ocean life and 70 percent of land life: plants, animals and even insects. Researchers had determined that these extinctions or "Great Dying" did not happen gradually, but quickly, almost at once. Natural reasons for extinctions, then, were probably not the answer.

Using a new statistical protocol for analyzing fossils, researchers found new fossil and geochemical evidence that points to an environmental mechanism for at least the largest extinction 251 million years ago, and possibly others. Using carbon records and other measures, these researchers now believe that the extinctions were caused by an oxygen-depleted ocean spewing forth poisonous gas. The culprit? Global warming.

To put it simply, when an ocean becomes anoxic (low or no oxygen), a certain bacterial life becomes abundant in the water. These microbes are generally found in the depths of stagnant lakes and create sulfur as a byproduct. The reason oxygen gets reduced in the atmosphere and thus the ocean is increased carbon dioxide. It is assumed that large-scale volcanic activity raised carbon dioxide levels, reduced oxygen, and lead to intense global warming. Active, spewing volcanoes alone cannot account for the extinctions in the water and on land of the Great Dying 251 million years ago.

But the increased carbon dioxide, decreased oxygen, and global warming created a friendly environment for those sulfur-creating microbes. These deep-dwelling microbes spew out large amounts of hydrogen sulfide. If the ocean or sea has enough oxygen, the hydrogen sulfide and oxygen stay separated and remain stable. If the ocean is lacking in oxygen, eventually huge bubbles of toxic hydrogen sulfide gas will erupt into the atmosphere. This strangling gas would have made the earth inhabitable as well. In addition to the poisonous gas, hydrogen sulfide attacks the ozone layer that protects life from the sun's UV rays.

And that is what scientists believe happen in several of the great extinctions of the past. This theory answers how both marine and land life disappeared at about the same time. This was long before humans and their carbon producing ways appeared. It seems as though the earth exterminated its own, and did so more than once.

This new evidence raises some interesting questions. It is generally accepted that human's contribution to carbon dioxide is accelerating global warming. The ozone layer is also being depleted in some areas. Scientists have found deformed fossil spores from the time of the Great Dying or extinction that resulted from extended exposure to high UV levels. And today, we can see rapidly decreasing supplies of healthy phytoplankton underneath holes in the ozone layer.

If several extinctions have already occurred because of short-term global warming, will it happen again? Do we have anything to fear from global warming? We don't know the rates at which carbon dioxide entered the atmosphere during each of the ancient extinctions. But the levels when the mass death occurred are known. At our current rate of climbing carbon dioxide levels, we are about 200 years away from conditions when oceans could become anoxic and trigger another extinction. Two hundred years isn't a long time in human history.

Will there be another extinction, this time involving humans? Let's hope we never have to find out!