Article: New Theory For Mass Extinctions
- From: "Robert Karl Stonjek" <rstonjek@xxxxxxxxxxxxxx>
- Date: Fri, 27 Oct 2006 16:38:22 -0400 (EDT)
New Theory For Mass Extinctions
A new theory on just what causes Earth's worst mass extinctions may help
settle the endless scientific dust-up on the matter. Whether you favor
meteor impacts, volcanic eruptions, cosmic rays, epidemics, or some other
cause for the worst mass extinction events in Earth's history, no single
cause has ever satisfied all scientists all the time for any extinction
event. That may be because big extinctions aren't simple events.
The new Press/Pulse theory gets around the controversy by rejecting the
all-or-nothing approach to mass extinction, calling instead on a combination
of deadly sudden catastrophes - "pulses" - with longer, steadier pressures
on species - "presses."
"What we wanted to do is move away from the idiosyncratic approach to
extinction mechanisms and look for what these intervals had in common. If
you have A and B you will get a mass extinction," said Ian West, a 2006
graduate of Hobart and William Smith Colleges in Geneva, NY.
West and Hobart and William Colleges paleontology professor Nan Crystal
Arens are scheduled to present their work on the Press/Pulse theory on
Wednesday, 25 October, at the Annual Meeting of the Geological Society of
America in Philadelphia.
Using databases that chart genera of marine organisms and their extinctions
through the fossil record, West and Arens divided the last 488 million years
of geologic history into four groups: times of suspected impact events
(Pulses), times of massive volcanic eruptions (Presses), times when neither
Presses nor Pulses occurred, and times when Press and Pulse coincided. They
compared average extinction rates in geologic stages in each of these
groups.
During stages when only impacts occurred, an average of 7.3% of genera
became extinct every million years; 8.3% of genera became extinct in stages
characterized by flood volcanism alone. When neither Press nor Pulse were
active, 8.2% of genera became extinct. These averages are statistically
indistinguishable. "Statistically speaking, extinction rates are not
significantly higher at times of impact or volcanism vs. no geologic
events," West said.
In contrast, when Press and Pulse events coincided, an average of 12.8% of
genera became extinct per million years, statistically higher than the rate
observed during other geologic stages.
"The goal of our work was to come up with a unifying theory of mass
extinctions. We also wanted to make it applicable to what's going on now,"
said West, referring to rapid losses of biodiversity worldwide now underway
as a result of climate change and destruction of habitats by human
activities.
"Is this model, which seems to work for the big five mass extinction events
in Earth's history, applicable today?" West asked.
At first glance the answer would appear to be 'no.' There is, after all, no
massive flood basalt eruption underway today, nor have there been any recent
meteor impacts. On the other hand, some very similar effects are being seen
on Earth.
"We came up with the idea that humans themselves act as both Press and a
Pulse," said West. "Humans began manipulating the environment - the Press -
from the advent of agriculture. However, that alone did not trigger the
current mass extinction. That seems to have been triggered by the pulse of
industrialization and the demands for energy and resources that came with
it."
The bottom line, says West is that it's extremely hard to pinpoint simple
causes for Earth's great periods of extinction.
"We sought to rephrase the question," said Arens. "In the modern world,
species are commonly endangered by some stress before the final death blow
falls. It seems likely that biological systems in the past worked in similar
ways. By demonstrating that the coincidence of long-term stress and
catastrophic disturbance is needed to produce big extinctions, we hope to
break down some of the polarization characteristic of many discussions of
extinction. We hope to send people back to the data with a more inclusive
hypothesis to test."
Source: Geological Society of America
http://www.sciencedaily.com/releases/2006/10/061025085208.htm
Posted by
Robert Karl Stonjek
.
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