Earth experiencing sixth great mass extinction; this one may be caused by humans (updated)

Tigers. Photo: Dave Page/

Updated 10/19/2010)

While everyone realizes that there have been mass extinctions in the past, most famously one that included the demise of the dinosaurs, few realize that, right now, we are in the midst of an equally cataclysmic event; the sixth great mass-extinction in the planet’s history.

This one may be turning into the largest – and fastest – extermination of life ever recorded, to the tune of about 30,000 species per year, according to Paleontologist Dr. Niles Eldredge.

That’s three per hour.

This time, it may be our fault.

Throughout the planet’s history there have been five mass extinctions  caused by astronomic, geologic or volcanic events. These were, according to paleobiologist Doug Erwin of the Smithsonian Institutions National Museum of Natural History, and the late John J. Sepkoski at the University of Chicago:

• Ordovician-Silurian extinction, about 439 million years ago, apparently caused by global temperature changes.
• Late Devonian extinction, about 364 million years ago. Cause unclear.
• Permian-Triassic extinction, about 251 million years ago, perhaps due to a combination of volcanic activity and comet or meteor impacts, or according to a new theory, the effects of giant salt lakes. About 90 percent of all life on Earth was destroyed.
• End Triassic extinction, roughly 199 million to 214 million years ago, most likely caused by volcanic activity
• Cretaceous-Tertiary extinction, about 65 million years ago, probably caused by asteroid impacts. This was the last one, the one that killed off the dinosaurs.

Then, as glaciers retreated at the end of the last ice-age, humans began not just hunting with more and more efficiency, but practicing agriculture.

According to paleontologist Dr. Niles Eldredge, Curator-in-Chief of the permanent exhibition “Hall of Biodiversity” at the American Museum of Natural History and adjunct professor at the City University of New York;
 

• Agriculture represents the single most profound ecological change in the entire 3.5 billion-year history of life. With its invention:
• humans did not have to interact with other species for survival, and so could manipulate other species for their own use
• humans did not have to adhere to the ecosystem’s carrying capacity, and so could overpopulate

 All clues point to the conclusion that this massive loss of species is caused by human activity, starting after the last glaciation period.

When the ice began to recede and agriculture arose, humans spread across the globe. As they did, entire species began vanishing. Hunting, deforestation and the introduction by humans of foreign diseases and species into new lands, have all had devastating effects.

Right now the list of species we’re losing is mind-boggling. Humans are already responsible for the loss of the dodo, moa, passenger pigeon, Carolina parakeet, Tasmanian tiger, Stellar’s sea cow, great auk, aurochs, Barbary lion and others.

The list of animals on the brink now is almost inconceivable  and includes: tigers, lions, eagles, kites, salmon, pandas, dozens of parrot species, cheetahs, sea turtles, orcas (killer whales), elephants, maned woves, Cape hunting dogs, rhinos, honey bees, butterflies, sugar-maple trees , wild apricots, wild almonds, acacia trees, cactus, mussels, condors, bats, all the great apes, frogs and other amphibians – and this is barely scratching the surface.

Consider just the obvious: No salmon to eat. No honey. No maple syrup. No food crops other than grains (as fruits etc require pollinators like bees and bats.) No natural twine (requires pollinators). No songbirds. No butterflies. Virtually no flowers (they also require pollinators). No great predators such as tigers or lions. Again, this barely scratches the surface.

What about less obvious side-effects on things like clean drinking water, erosion, soil organisms (which will affect agriculture), forests, diseases and oceans?

The answer is; we don’t know. What we are learning however, is that the long-term effects may have serious ramifications.

Take the extinction of the Dodo, for instance. The ‘ripple or domino effect’, caused by the destruction of this large, flightless bird on the Mauritian Island ecosystem it inhabited, have taken over 300 years to become apparent.

Calvarias major, a local tree species, is now endangered as a direct result.

The Dodo and the Calvaris depended on each other. Only the dodo could crack the tree’s hard-shelled seeds as it fed on the seeds. The dodo’s gizzard (a second stomach for grinding food) would weaken and crack the seed’s hard outer coat, without harming the seed itself. The seeds would then be deposited back onto the ground in the birds droppings, and grow into new trees.

Today there are no more new trees. The old trees keep dropping seeds, but without the Dodo there to eat them, none germinate. The tree is functionally extinct.

All because of the extermination of one kind of bird.

Lastly, to illustrate how our activities are changing the face of the globe, consider that throughout history the earth has experienced cycles of cooling and warming, called Milankovitch Cycles. These are the natural astronomical cycles are responsible for our seasons. .

According to models, the earth is actually in a cooling period – a mini-ice-age as it were. Alarmingly, human activity has not only negated this natural effect of the Earth’s orbital distance from the sun, but our planet is actually heating up despite it.

All these disruptions of the Earth’s carefully and intricately designed systems risk causing more imbalances than the planet can compensate for.

The web of life is so vastly complicated and interwoven, that every day startling new revelations are made by researchers. Even one tiny piece of the puzzle (say, grizzlies feeding on dying salmon), impacts the life cycles of a mind-boggling number of other animal and plant species -- and with other systems that humans depend upon, such as river systems. Such ‘keystone’ species are crucial and must interact with the other species in the web to maintain the integrity of the whole.

We are losing huge segments of this ancient fabric.

Humans are playing a dangerous, dangerous game of ‘Russian roulette’.

While the Earth itself will undoubtedly survive, the world we know may not.

Paleontologist Dr. Niles Eldredge is Curator-in-Chief of the permanent exhibition “Hall of Biodiversity” at the American Museum of Natural History and adjunct professor at the City University of New York. He has devoted his career to examining evolutionary theory through the fossil record, publishing his views in more than 160 scientific articles, reviews, and books. Life in the Balance: Humanity and the Biodiversity Crisis is his most recent book.

You may also find of interest:

End the dolphin slaughter

Wildlife faces cancer threat

End Mountaintop-removal coal mining

One Day at Teton Marsh (a book for children on ecosystems.)

Star Trek's Spock faces extinction (a light-hearted title for a serious subject)