Posted on 10/16/2003 7:33:43 AM PDT by AntiGuv
The Cambrian Explosion - when life suddenly and rapidly flourished some 550 million years ago - may have an explanation in the reaction of primitive life to some big event.
The explosion is one of the most significant yet least understood periods in the history of life on Earth.
New research suggests it may have occurred because of a complex interaction between components of the biosphere after they had been disturbed by, for example, the break-up of a super-continent or an asteroid impact.
Scientists say the life explosion might just have easily occurred two billion years earlier - or not at all.
Dramatic events
All modern forms of life have their origin in the sudden diversification of organisms that occurred at the end of the so-called Cryptozoic Eon.
Scientists have struggled to explain what might have happened in the previous few hundred million years to trigger such a burst of life.
Certainly, it was a period of history that witnessed the assembly and break-up of two super continents and at least two major glaciation events. Atmospheric oxygen levels were also on the rise.
But what actually caused the Cambrian Explosion is unknown.
Writing in the journal Geophysical Research Letters, Dr Werner von Bloh and colleagues, from the Potsdam Institute for Climate Impact Research, present a new analysis of happened.
They suggest that "feedback" in the biosphere caused it to jump from one stable state without complex life to one that allowed complicated life to proliferate.
"We believe that there was a change in the environment - a slow cooling of the system - that caused positive feedback that allowed the conditions for complex life," Dr von Bloh told BBC News Online.
Self regulation
Using a computer model of the ancient Earth, the researchers considered three components of the biosphere, the zone of life.
These were single-celled life with and without a nucleus, and multicellular life. Each of these three groups have different environmental tolerances outside which they cannot thrive.
The computer model showed there were two zones of stability for the Earth - with or without higher lifeforms - and that 542 million years ago the planet flipped from one to the other.
What caused the flip is not clear. It might have been a continental break-up, or even an asteroid impact.
There is some indication that the Moon suffered a sudden increase in impacts about the same time as the Cambrian Explosion. If so, then the Earth would have been affected as well.
This latest analysis also provides some support for the Gaia hypothesis - the idea that the biosphere somehow acts as a self-sustaining and regulating whole that opposes any changes that would destroy life on Earth.
Intelligent beings
Dr von Blow says that after the Cambrian Explosion there has been a stabilisation of temperature up to the present, and that the biosphere is not playing a passive role.
He also adds that there is an intriguing implication from his research which suggests that had the conditions been only slightly different, the Cambrian Explosion could have occurred two billion years earlier.
An early explosion would have meant that by now the Earth could have developed far more advanced intelligent creatures than humans.
Alternatively it could still be inhabited by nothing more complex than bacteria.
Dr von Bloh says that it will be of great interest when we find other Earth-like worlds circling other stars to see if they have had their own Cambrian explosions yet.
The timing of such events has implications for the search for intelligent life in space, he says.
I don't not believe in god, I just want to see physical proof.
Word History: An agnostic does not deny the existence of God and heaven but holds that one cannot know for certain whether or not they exist. The term agnostic was fittingly coined by the 19th-century British scientist Thomas H. Huxley, who believed that only material phenomena were objects of exact knowledge. He made up the word from the prefix a-, meaning “without, not,” as in amoral, and the noun Gnostic. Gnostic is related to the Greek word gnosis, “knowledge,” which was used by early Christian writers to mean “higher, esoteric knowledge of spiritual things” hence, Gnostic referred to those with such knowledge. In coining the term agnostic, Huxley was considering as “Gnostics” a group of his fellow intellectuals“ists,” as he called them who had eagerly embraced various doctrines or theories that explained the world to their satisfaction. Because he was a “man without a rag of a label to cover himself with,” Huxley coined the term agnostic for himself, its first published use being in 1870."
The questioning seldom comes from a position of knowledge, though. Most of the time, when a creationist tries to point out flaws in the ToE, it turns out these have already been addressed by biologists -- sometimes many years before. In reality, most of the objections to evolution seem to boil down to "I don't want to believe I'm related to monkeys, therefore evolution is full of holes."
My understanding of an agnostic is one that does not necessarily believe that G*d exists but is open to the possibility.
They will not believe unless given/shown physical proof that there IS a G*d.
What that proof would be I can't say. It would probably be different for each person.
Christ's journey into hell is described in the Gospel of Nicodemus. This book didn't make the cutoff.
Lucky Strike Means Fine Tobacco.LOL!LSMFT QED...
Some might have contempt, but science is not science without the assumption of uniform natural laws over time. Of course scientists assume the holes will be plugged. That's their job.
There have been new phyla since the Cambrian; not very many, true, but two or three (I think). It's on the talk.origins FAQ.
One of the interesting things about almost all our phylogenetic trees is how deep-rooted they are. What I mean by this is that the three or four main placental mammalian branches diverged very close to the common ancestor of all placental mammals; the birds, likewise, branched into major orders way back, and so on. Moreover, much of this branching seems to be associated with mass extinction, most prominently the CT boundary. My speculative explanation for this would be that the mass extinction opened up a huge number of ecological niches, while similarly exterminating almost all the efficient predators. Organisms which weren't initially specialized to fill particular roles, and would have been out-competed before the extinction, filled them, and were in turn able to specialize themselves.
If bodies are being created randomly by mutation, I would expect body plans found in nature to be far more diverse than the SciFi creatures designed by Hollywood.
I'm not sure that's how body plans were created. My SWAG would be that most major changes were caused by mutations in the developmental genes, which might have added a pair of legs, or changed the shape of a limb, or whatever. But I'm not sure you could throw up a truly wild body plan by that mechanism. Most radical changes are, after all, lethal.
I could point you to one still posting, and a couple who have been banned. I could point to one who is active this week who considers anyone who disagrees with him to be morally insane. I'm not going to name them. They will show themselves.
These are folks who never vary their pitch. There are lots on both sides that have an occasional tantrum.
For one thing, the longer you've had a body plan, the more committed you are to it. The Cambrian phyla, like the Vendian ones before them, are surprisingly similar in their size and simplicity--the lack of "derived" characteristics. They don't look all that far diverged from each other, despite the differences in body plan. Nowadays, some members of the chordate phylum can be a lot bigger and more complex than, say, worms or sponges, but the Burgess Shale species don't show the same kinds of diversity. (Although they do come in a lot of bizarre forms.)
This article is about what exactly triggered the burst of experimentation with greater complexity. (Doesn't give much of an answer, I admit.) Whatever caused it, something did. Experimentation with body plans, at least initially, was pretty much inevitable in that process. You're just discovering complex multicellular adaptations and it's really unknown territory.
Well, some body plans work and some don't. When you get one that works and have gone on to experimenting with details beyond that, you're unlikely to get rich throwing all your investment away. Especially if you have competition out there literally trying to eat you up.
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