Posted on 05/20/2003 11:01:28 AM PDT by Mike Darancette
Scientists studying rocks near an ancient asteroid impact structure in South Australian have uncovered evidence that could change current theories explaining how life on Earth rapidly diversified about 580 million years ago.
Dr Kath Grey of the Western Australian Department of Industry and Resources' Geological survey and an ACA associate researcher, Prof Malcolm Walter, Director of the ACA and Dr Clive Calver of the Tasmanian Department of Mineral Resources challenge the idea that 'Snowball Earth' - an intense period of glaciation about 600 million years ago, triggered the evolution of simple life forms into more complex and familiar species.
In the May edition of the international journal Geology, Dr Grey and her team put forward an alternative radical idea that 580 million years ago an asteroid impact played a pivotal role in this evolutionary jump. The impact, known as the Acraman event, smashed a hole in South Australia about four times the size of Sydney.
Up until then, for the first three billion years of Earth's 4.5 billion year history, bacteria and simple algae had dominated life on Earth. "Then almost overnight geologically speaking, the ancestors of modern day animals and plants appeared in the fossil record about half a billion years ago," Dr Grey said. "The big question is what caused the rapid proliferation of life at that time?"
Research by other scientists suggests the evolutionary burst of life between 600 and 540 million years ago was the result of an intense period of global glaciation. However, if the findings of Dr Grey's research prove correct, the cause could lie beyond our planet.
Dr Grey, who has studied fossil plankton (single-celled green algae) from drill holes across Australia, has found that, as predicted by the Snowball Earth theory, bacterial mats and a few simple spherical species of plankton were the only organisms that managed to survive the intense ice age.
"As the sea level rose at the end of the ice age, these spherical forms increased in number," Dr Grey said. "But there is no sign of a new species emerging at the end of the intense ice age to support ideas of the rapid diversification of life at this time."
Dr Grey believes it wasn't until about 20 million years later more than 50 new and highly complex species suddenly replaced the small number of simple species in the fossil record.
"What is really interesting is that the more complex spiny fossils appear just above a layer of rock in South Australia associated with the Acraman impact," Dr Grey said.
In a related study, Dr Calver found significant carbon isotope changes mirrored Dr Grey's observations. Prof Walter has also noted that patterns associated with the Acraman impact were similar to those of mass-extinction and recovery events, and that a large asteroid impact could have produced conditions ideal for evolutionary change.
"Later impacts, like the 65 million year old Chixulub collision in Mexico wiped out a diverse range of species, including the dinosaurs," Dr Grey said. "But with the Acraman impact, there were only a small number of species around and the time to cause a mass extinction event.
"Most of the species that did survive were highly resilient, and had the ability to remain dormant through the cosmic winter that followed. When conditions improved, these species had an advantage over their competitors and were able to proliferate and diversify."
Dr Grey and her team have reasoned that the ensuing plankton diversification must have played a vital role in the subsequent development of the animals dependent on plankton as a food source.
Birds were top predator for a short time world wide and for quite a while in what was then a geographically isolated South America. But birds did not radiate many species to fill other ecological niches.
Mammals basically radiated to fill all ecological niches and quickly gained ascendancy.
When South America was finally connected to North America the Big Cats quickly gobbled up the Terror Birds.
But again -- the ice age they're talking about was an extreme environmental stress, too, and they note that diversification didn't occur afterwards. This particular claim seems to tie diversification the asteroid impact.
Which is fine, but let's just be clear about the underlying assumptions of the claim.
That is not relevant to the premise of the article.
The ice age was a gradual thing and the various species extent at the time had plenty of time to adapt. The meteor impact threw that whole primordial paradise into a tizzy, stressing the environment and rendering some species extinct and opening up new ecological niches to the survivors.
Or, rapid speciation had already occurred in an isolated environment (a lake or small sea) while species in the outside world went on their fat, dumb and happy ways. When the asteroid hit it not only stressed the latter group but opened up the wider world (and new ecological niches) to the formerly isolated group.
Or, much like the last scenario, but with a group from the wider world being geographically isolated by the asteroid impact, and rapidly evolving in isolation (small groups evolve much more rapidly because changes are not as readily lost as they are in larger gene pools). Later this group rejoined the world at large.
There was no selection pressure favoring the new mutants. They were born and died out, ending their genetic influence, or limited to very small populations who didn't happen to leave a fossil record.
When conditions change, those few mutants who earlier may have had relatively expensive requirements compared to their simpler cousins, suddenly had a survival or re-population advantage.
I think you'll find that most higher complexity organism have initially higher "expenses" and therefore have a hard time getting a toe hold in a well settled niche. But when something comes along and upsets the apple cart, those few who've managed to pay that initial expense can now exploit that capital.
Complexity of organization requires an initial investment. Simpler organism can get into production quicker, and so tend to win the early races. But they are often less robust in the face of changing conditions. The more complex creature was paying for some unused abilities, and suddenly that is the difference between life and death -- or at least speed to repopulate.
I thought that's where this article was going too - we're all space aliens.
I guess the theory of this article is that the asteroid slapped the earth out of it's torpor, kinda like the scene in B movies when the guy slaps the gal and yells "snap out of it"!
But there was life on Earth BEFORE the Impact Event and Ice formation described in the article, life that was ancesteral to life that existed afterward.
As to how life first formed upon this planet ......
Come now. Let's get our stories straight. Birds are dinosaurs are they not?
Ask your average paleontologist who is familiar with the phylogeny of vertebrates and they will probably tell you that yes, birds (avians) are dinosaurs. Using proper terminology, birds are avian dinosaurs; other dinosaurs are non-avian dinosaurs, and (strange as it may sound) birds are technically considered reptiles. Overly technical? Just semantics? Perhaps, but still good science.
Isn't this making up stories just so much fun!!?
No. Because that didn't happen
Oh bother, such petty details!
Speaking of details. How deep was the ice sheet over snowball earth and how large was its extent?
Better?
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