Mass extinctions not as fast as expected

[Damien]

Mass extinctions are not sudden, it seems that it takes a while for a population to die out after a major cataclysm:

Dinosaurs 'lived for 300,000 years after Mexican meteor strike'
JOHN VON RADOWITZ

DINOSAURS were killed off by a meteor that hit the Earth 300,000 years after the one blamed for their extinction, a scientist has claimed.

Dr Gerta Keller, from Princeton University, New Jersey, insists the Chicxulub impact off the coast of Mexico 65 million years ago could not on its own have wiped out the dinosaurs.

Full article here

The impact did not kill off the dinosaurs and other species that were wiped out 65 million years ago, smaller populations existed as the climate changed and the earth settled, but it became unsuitable for their existence - previous ecosystems no longer existed or were distorted.  Could it be that humans are on the slow trail to extinction?  I'd be interested to read your thoughts.

[Orstio]

It makes more sense, actually, that many (if not most) species would continue to survive with dwindling numbers while those less-suited to the new environment would decrease in number until extinct.  This was probably variable:  For some species, just a few generations, for others, a few hundred generations. 

The fact that several species of mammals survived the catastrophe that caused the extinction of the dinosaurs is a good indication that not everything went extinct at once. 

As for humans, I think we need to understand that we are but one species of the millions (billions?) of species of organisms on the planet.  If we went extinct, it would be catastrophic only for ourselves.  The rest of the planet would probably not care a great deal.  We need to understand that an event like that at the end of the Cretaceous killed off 50-60% of the species on the planet.  It makes our one species seem rather insignificant.

As for our slow extinction, I highly doubt it.  If anything, we are headed into an age of even higher population growth.  Our technology is at a level that will ensure our survival under almost any circumstances.  That, and, as a species, the span of our existence is measured in thousands of years, not the millions of years that some species of dinosaurs existed.  We need to understand that a creature that lives within a certain environment, and adapts to fully capitalize on that specific environment, is far more susceptible to extinction when the environment changes.  I think humans have shown that we can adapt to pretty much any environment, probably because as a species, we have not been given the opportunity to live in a specialized environment for any lengthy geologic period of time.

[Retrospector]

I saw this story on AT&T Yahoo! news this morning. This article is from livescience.com

http://www.livescience.com/environment/061027_mass_extinction.html

Apocalypses may not be all fire and brimstone. A growing number of paleontologists say that Earth-smashing meteors cannot take all the blame for the many mass extinctions that dot our planet's fossil record. The true causes seem to be more complex.

"The [meteor] impact model has been so successful because it's easy to explain and easy to understand," said Nan Arens of Hobart and William Smith College in Geneva, NY. "However, the simple answer isn't always the best one."

At the annual meeting of the Geological Society of America this week in Philadelphia, Arens and others argued that the combined punch of volcanoes, climate change and impacts leaves many species teetering on the brink of extinction. One final blow brings collapse.

The argument in this article isn't that we are missing the evidence for the "really big" impact event, but that extraterrestrial impacts may be just part of the picture.

Back about 20 years ago, paleontologists like Niles Eldredge and Stephen Jay Gould were saying much the same thing. Together they are (or were in the case of Gould) leading proponents of the "punctuated equilibrium" mechanism in evolution. Gould was certainly more enthusiastic than Eldredge about the possible primary role of extraterrestrial impacts in setting the course of life on Earth, I remember a distinct note of skepticism about the idea in Eldredge's book "Lifepulse". But still, both were careful to point out the complex mechanisms of environmental change that appear to have also played roles in mass extinctions.

I think that the idea of multiple extinction mechanisms isn't new to the scientists in the field. It's just that the popular science press has seized on the impact idea and sold an overly simplified version to the public, because the idea is so easy to grasp.

As for our current situation, I subscribe to the view that we may be in another age of widespread extinction - which may have even begun long before the explosion of the human population and the modern exploitation of environmental resources - but things are still happening on a timescale too slow for human beings to perceive.

[Damien]

multiple sources definitely makes sense - in the K-T boundary case - it is quite possible with climate change, sea level wild fluctuations, an impact, mass volcanism (Deccan traps) and possibly disease etc - that the dino's did not have muich of a chance

I must say the Permo-Triassic extinction intrigues me more - as this seems to have been far worse than the KT

[Retrospector]

Paleontologists would generally agree that the P-T extinction event was more far-reaching than was the K-T. For the general public though, most everyone knows what dinosaurs were, fewer know about marine animals such as trilobites which finally came to an end with the close of the Paleozoic. Plus there's been so much press since the 80s or so about the K-T boundary and the extraterrestrial impact theory.

And I guess that another factor is that the P-T event is much further back in time and therefore more difficult to quantitatively analyze.

[Astronuc]

I think that extinctions can occur relatively quickly, and it doesn't take a cataclysmic event such as a meteor.  Mass extinctions can occur over several decades with loss of food, disease, climate change, . . . .

Consider -

The evolution of the species: a story of thriving mammals and dying dinosaurs

They are the only warm-blooded, furry creatures that can feed their young on milk and now it seems the dominance of mammals has more to do with flower power than dinosaur disaster.

A comprehensive family tree of the 4,500 mammalian species alive today has punctured the enduring tale that links the sudden death of the dinosaurs 65 million years ago with the rise of mammals.

Instead, the study found that the period when mammals underwent their greatest evolutionary explosion coincided with the arrival of flowering plants during the Eocene epoch 56 to 34 million years ago.

Alternatively, the rise might have been the result of a change in the climate - a period of global warming long after the dinosaurs became extinct - which allowed mammals to flourish.

Yesterday, I heard a report on the fact that crustaceans, e.g. crabs and various other shell fish, are disappearing because of the overfishing of large sharks, such as hammerhead, dusky bull sharks and others.  The large shark prey on rays and skates, and the rays and skates, which are now unchecked, feed on shellfish.

Overfishing of sharks makes scallops vanish: study

WASHINGTON (Reuters) - Overfishing of big sharks in the Atlantic has cut stocks by 99 percent, dooming North Carolina's bay scallop fishery and threatening other species including shrimp and crabs, researchers reported on Thursday.

With most of the great predatory sharks -- bull, great white, dusky and hammerhead -- gone from northwest Atlantic waters, the rays and skates the sharks normally feed on had a population explosion, the scientists said in the journal Science.

"With fewer sharks around, the species they prey upon -- like cownose rays -- have increased in numbers, and in turn, hordes of cownose rays dining on bay scallops have wiped the scallops out," said study co-author Julia Baum of Dalhousie University in Halifax, Nova Scotia.

Bull, dusky and hammerhead sharks have declined by more than 99 percent between 1970 and 2005, Baum said in a statement.

This coincided with a rise in Asian demand for shark fins for medicinal uses and for food. Shark fins currently sell for about $22 a pound, Peterson said, citing a local fisherman.

Now that the ravenous rays and skates have feasted on bay scallops, they are likely to look for food in protected areas along the coast where other fish and shellfish shelter in their early months of life, said co-author Charles "Pete" Peterson of the University of North Carolina at Chapel Hill.