[meteorite-list] Extinction Theories Abound

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Jul 13 21:01:26 2004
Message-ID: <200407140101.SAA02205_at_zagami.jpl.nasa.gov>

http://www.abqtrib.com/archives/news04/071204_news_bright.shtml

Extinction theories abound
By Sue Vorenberg
Albuquerque Tribune
July 12, 2004

Spencer Lucas is gearing up for a scientific smack-down.

The curator of the New Mexico Museum of Natural History & Science has a
theory that one of the five biggest mass extinctions in Earth's history
wasn't really a mass extinction at all.

Most scientists think a mass extinction that helped give rise to the age
of dinosaurs - about 208 million years ago during the late Triassic -
was caused rapidly by one big meteorite impact.

Lucas disagrees. He thinks there were actually several smaller
extinctions over a period of about 10 million years which helped spur
the dinosaur expansion, possibly caused by changes in sea level and
global climate change.

"Nobody's been looking at this - these guys have all missed what's
really going on," Lucas said with a playful grin. "All I'm trying to do
is convince my colleagues that this was a prolonged extinction. It's not
one of the big five - take it off the list."

Science is supposed to be a field of constant change, where new theories
with better evidence replace older ones, Lucas said. With change comes
debate, heated arguments and sometimes a downright entrenched resistance
to new ideas.

That aspect of science couldn't be more fun, Lucas said.

"When you publish on something it's hard to back down later and say you
were wrong," Lucas said. "But that's the nature of scientific debate.
One friend of mine who really thinks this extinction was caused by a
meteorite - I'm embarrassed for him. I told him in five years you're
going to regret this."

The evidence of a mass extinction during that time period are sketchy at
best, Lucas said. The fossil record from the time period comes from
different rock beds all over the world - and those rock beds aren't
necessarily all from the same time period.

"It seems that poor stratigraphic records are all mashed together,"
Lucas said. "Most people would argue 40 to 60 percent of species went
extinct then, but I'm not convinced that all happened at the same time.
There's just a lot of problems determining the exact ages of things in
the late Triassic."

Several types of sea creatures called ammonites went extinct during the
late Triassic, as did some reptiles and large amphibians.

For the past 20 years most scientists have believed the extinction was
caused by the 212-million-year-old, 61.2-mile diameter Manicouagan
crater in Northern Quebec. Many scientists still believe that theory.

"Current data can be explained by the impact of one or more asteroids or
comets that terminated biotic diversity, which otherwise was rising
through the late Triassic," said a 2003 paper by Paul E. Olsen, a
paleontologist at Columbia University who champions the impact theory.

That crater isn't nearly as big as the 105.6-mile diameter Chicxulub
crater that most scientists think killed the dinosaurs 65 million years
ago, Lucas argues.

"Even if Manicouagan were the right age - and I don't think it is
because it happened several million years before this so-called mass
extinction - I'm not sure it was big enough to cause a mass extinction,"
Lucas said. "It isn't anywhere near as big as Chicxulub."

But aftereffects of the Manicouagan impact seem similar to those of
Chicxulub, Olsen has argued.

"As with the (dinosaur extinction 65 million years ago), reduced
sunlight and lower temperatures plagued continental biotas for months,
and the global carbon cycle . . . was massively perturbed," Olsen's 2003
paper said.

Lucas admits Manicouagan could have started off his 10-million-year
period of gradual extinctions by disturbing the environment, but he
doesn't think the changes happened as fast as Olsen believes.

"I think it must have been the result of a series of ecological crises,
possibly driven by more than one impact, possibly driven by changes in
sea level," Lucas said. "But you have to ask yourself - a series of
extinctions that wipe out 40 percent of species over 10 million years,
how unusual is that?"

The phenomenon might not be all that unusual, which is why Lucas said
the event should be taken off the biggest mass extinctions list.

"In the end of the Triassic you had a series of sea level changes that
could have disrupted the marine ecosystem," he said. "The world at that
time looked very different. The continents were still pretty much
together in Pangea, but it was breaking up. Most of the land mass was
centered around the equator - with not much beyond 60 degrees latitude
or so."

The climate was warmer and there were no polar ice caps. There were also
no flowering plants on land - the plant life was mostly ferns.

"Dinosaurs were just appearing at that time," Lucas said. "Their
appearance might have had a negative effect on these other animals. You
could argue that. Dinosaurs were far better adapted to life in the
Jurassic."

Mostly what Lucas says he wants is for scientists to start looking at
the possibility that the extinctions during that time period weren't as
extreme as previously believed, he said. The theories as to why it
happened can come later.

"It's easy to wrap your mind around a single impact causing a single
extinction," Lucas said. "It's harder to understand multiple extinctions
with multiple causes over a long period of time."


Received on Tue 13 Jul 2004 09:01:12 PM PDT