May 30th, 2012
- This is the way the world ends
- Not with a bang but a whimper.
- "The Hollow Men" by T.S. Eliot (1925)
Econintersect: It has been believed by many that the great mass extinction events were caused by sudden cataclysms, such as a massive asteroid impact or gigantic volcanic eruptions. There have been many, some not even identified, mass extinctions; but only five have achieved the characterization “great” mass extinction. Researchers now believe that only one of these five mass extinction events known for earth’s history was associated with a cataclysmic event. The tell-tale signs have been found in the geological record that has been studied in recent decades. What caused the other four mass extinctions? The evidence points to the occurrence of “sick earth syndromes.”
Research published in 2006 gave a good description of one form of sick earth syndrome that might of occurred and is supported by research data. From Science Daily:
The Permian-Triassic extinction, as it is called, is not the one that wiped out the dinosaurs. Nor does the cause appear to have been a meteorite strike, as in that famous event.
The most likely explanation for the disappearance of up to 90 percent of species 250 million years ago, said David Bottjer, is that "the earth got sick."
Bottjer, professor of earth sciences in the USC [University of Southern California] College of Letters, Arts and Sciences, leads a research group presenting several new pieces of the P-T extinction puzzle.
Matthew Clapham, a recent Ph.D. graduate of Bottjer's laboratory, has found that species diversity and environmental changes were "decoupled" long before the extinction. Conditions on the planet were deteriorating long before species began to die off, Bottjer said, casting doubt on the meteorite strike theory.
"People in the past used to think this big mass extinction was like a car hitting a wall," he said. Instead, Clapham's interpretation of the geological record shows "millions of years of environmental stress."
Pedro Marenco, a doctoral student in Bottjer's lab, has been testing a leading theory for the P-T extinction: that a warming of the earth and a slowdown in ocean circulation made it harder to replace the oxygen sucked out of the water by marine organisms. According to the theory, microbes would have saturated the water with hydrogen sulfide, a highly toxic chemical.
For a mass extinction "you really needed a good killer, and it [hydrogen sulfide] is really nasty stuff," Bottjer said.
Marenco has measured large changes in the concentration of sulfur isotopes that support the hydrogen sulfide theory.
Cataclysmic events may have been involved in mass extinctions but they may have had effect in collaboration with other factors such as climate changes that were not related. The resulting toxicity of the planet then became a killer.
Click on the following graphic for an interactive geologic timeline of the earth showing major extinction events (from Discovery Channel). Note: The graphic does not reflect all of the information presented in this article covering the latest research results.
The one mass extinction that has been associated with a cataclysm, a large asteroid strike into what is now the Gulf of Mexico, was the proximate cause of the extinction of dinosaurs 65 million years ago. Along with the giant reptiles and bird precursors, many other life forms also suffered total or almost total demise. But, as opposed to the other four mass extinctions, the most recent which was thought to be global in extent until recently was actually much more severe and recovery took much longer in the northern hemisphere. Many lower life forms actually survived the event in the southern hemisphere while being largely exterminated in the northern half of the globe. The reason? Toxic material, largely elemental metals were much more concentrated closer to the impact zone. Thus North America and the North Atlantic suffered the worst devastation.
And in the four non-cataclysmic mass extinctions, which took many millenia to develop (and may have continued for millions of years), recovery also took a long time, possibly millions of additional years.
In addition to the five global mass extinctions, others have occurred on a more localized basis. Half of North America’s large mammals became extinct over a 2,400 year period 11,000 to 14,000 years ago. This may possibly be part of a more global extinction process that started about 50,000 years ago. Over a period of approximately 47,000 years 65% of all mammals weighing more than 44kg (97 lb) went extinct. This span of time covers the entire last ice age which peaked about 21,000 years ago. However, the North American event was so compressed in time and coincides with the arrival of humans in significant numbers from Asia that the rapid extinction of North American may have had human interaction as a significant component.
A modern day mass extinction event may be unfolding over the last century and in the coming years. According to Kate Wong, Paleontologist Catherine Badgely, University of Michigan, 25% of mammals and 25% of birds have become extinct or are endangered. The current effects are primarily due to habitat destruction by an expanding human population.
- Extinction by Asteroid a Rarity (Carl Marziali, USC News, 7 October 2007)
- Mass extinction’s Cause: ‘Sick Earth’ (Science Daily, 21 October 2012)
- It Took Earth Ten Million Years to Recover from Greatest Mass Extinction (Science Daily, 29 May 2012)
- Tiny Shelled Creatures Shed Light On Extinction and Recovery 65 Million Years Ago (Science Daily, 1 March 2012)
- Mass Extinction: Why Did Half of N. America’s Large Mammals Disappear 40,000 to 10,000 Years Ago? (Science Daily, 27 November 2012)
- Climate Change Played Major Role in Mas Extinction of Mammals 50,000 Years Ago, Study Finds (Science Daily, 18 May 2010)
- The Current Mass Extinction Kate Wong, Scientific American, 30 October 2012)
- Mass Extinctions Timeline (Discovery Channel, not dated)