The Minority Report

   MASS EXTINCTIONS  

MASS EXTINCTIONS HAVE CHANGED THE EARTH FIVE TIMES.

 RELATED WEB PAGE:   "Final Impact," The Day the Dinosaurs Died.

For hundreds of millions of years, climate-changes have been responsible for the extinction of vast numbers species. "Global warming" or "global cooling" can occur unexpectedly. The most extreme of recent examples is that of the Younger-Dryas Event that ended about 9600 B.C.

No one knows with certainty its cause. The prevailing theory holds that the Younger-Dryas was caused by a significant reduction or shutdown of the North Atlantic thermohaline circulation in response to a sudden influx of fresh water from Lake Agassiz and deglaciation in North America [5]. The global climate would then have become locked into the new state until freezing removed the fresh water "lid" from the north Atlantic Ocean. This theory does not explain why South America cooled first.

12,900 to 11,500 years ago, ice fields covered the globe. Most people assume that climate change tends to develop over a long time. That isn't necessarily true.

In 10,900 B.C., the temperature plunged from a warming period to freezing conditions in just ten years. In what is now the United Kingdom, the average temperature was -5 degrees centigrade.

In 1300 A.D. the "Little Ice Age" began for reasons unknown and lasted 500 years until the mid-1800s. That period had followed a 400-year warming period that had allowed even colder climates like Greenland to become habitable. The Vikings lived in Greenland during that era of warming but abandoned Greenland at the onset of the Little Ice Age.

Europeans who had been accustomed to a warm climate for generations could no longer grow crops. Many migrated south while others scraped and starved. Around 1860, the climate began warming again and continues to warm to this day.

Although most areas of the globe are again heating, as has occurred many times in the past, the temperature could plunge into another ice age within 10 to 20 years at any time for reasons not understood. Although  high-profile environmental celebrities spout declarations of questionable science, the truth is that no one has the knowledge to make long-term predictions with any certainty.

New Scientist Magazine (published weekly for post-docs in science and medicine) reports that Peter Ward, paleontologist at Univ. of Washington, Seattle, has concluded that  we are now facing earth’s sixth mass extinction. ⁰² Ward’s sub-theory, that our earth now entering the time of another extinction event, is gaining ground.

Evidence exists to support Dr. Ward's assumption. No reputable scientist predicts that the human species will disappear along with environmentally sensitive life. But mammals, birds, plants, insects and marine life are disappearing at a rate unprecedented in human history.

The cause of climate warming cannot be proven. But it is now clear that our world will look far different within seventy-five to one hundred years from now than it does today. We're safe in assuming that no humans, SUV's or power plants existed in the first four events and similarly, no one has proven irrefutably that human activity is a factor in the mass extinction now in progress. Well-known environmentalists have many facts behind their claims. Yet no one has anywhere enough information on what causes climate change.

Astronomers at Harvard have noted that the Sun has been warming for 300 years. They believe this to be the cause of Earth's current warming phase. They do not insist that this is the only reason because no one can know that. The earth's own ocean currents and other planetary-borne factors are known to affect changes in weather.

According to two Duke University physicists, Earth's warming for the past two decades has been the result of solar output. Exhaustive studies from Duke University claim that human activities aren't the (at least principal) reason for global warming. Furthermore, say other scientists, the temperatures to which we're accustomed will return about the first of the next century.

Take your choice and believe what you wish. No one knows.

201 million years ago, the Triassic extinction wiped out 25% of all life. Marine animals suffered the most. Dr. Ward believes this and most others were caused by climate change.

251 million years ago, the Permian extinction killed 95 percent of the earth’s marine life and 70 per cent of its land animals. Massive volcanic eruptions in what is now Siberia covered the earth with carbon dioxide, a “greenhouse” catastrophe that robbed living creatures of sufficient plant life to sustain them. The atmosphere’s carbon dioxide level was 100 times that of today.

Most scientists believe, but none can conclusively prove, that pollutants produced by the large industrial nations are responsible for an ongoing greenhouse effect. A growing number of these claim that this trend is irreversible, even if all nations immediately reduce their pollutants to zero.

The 5 Great Mass-Extinction Events

(1)                 Ordovician-Silurian Extinction, 439 million years ago. Global cooling caused glaciers to form. As the glaciers formed, seal levels dropped. Then global warming ensued, causing the sea levels to rise again.  The death toll: 25 percent of marine families and 60 percent of marine genera.

(2)                 Devonian Extinction, 374 million years ago. 70% of all life, land and marine, vanished. Little is known of land animals of this time. Climate change appears to have been the cause, but no one is certain. 

(3)                 Permian-Triassic Extinction 251 million years ago. Earth's worst mass extinction event. All life almost died during this time. For 80,000 years, environmental events and climate change had been destroying sea and land animals. Flood volcanism from the Siberian Traps and related oxygen loss in the seas were part of the problem. An even worse disaster was about to befall Earth's inhabitants. The dominant land species were reptilian with mammal-like features, which inhabited Earth before the dinosaurs. Some researchers refer to these animals (example in painting above) as "half reptile-half mammal."

Ultimately a comet struck Earth, causing even greater flood volcanism at the end of the Permian era. 95% of all species were wiped out. The death toll: 53 percent of marine families, 84 percent of marine genera (the classification above species), and 70% of all land species that included plants, insects and vertebrate animals.

(4)                 End-Triassic Extinction, 214 million years ago, most likely caused by massive floods of lava erupting from the central Atlantic magmatic province -- an event that triggered the opening of the Atlantic Ocean. The volcanism led to deadly global warming. Rocks from the eruptions now are found in the eastern United States, eastern Brazil, North Africa and Spain.    

             The death toll: 22 percent of marine families, 52 percent of marine genera. Vertebrate deaths are unclear.

            The Triassic period’s carbon dioxide level of 200 million years ago was recently learned to have been 100 times more than in today’s atmosphere. Paleontologists determined this by studying isotopes in rocks dating from that period.