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     Precambrian Period

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Demon38

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The Precambrian period lasted from the begining of the earth (4.6 billion years ago) to about 570 million years ago.  It's been the subject of numerous inaccurate creationist claims, I'd like to correct their misconceptions in this thread.
Creationists like to claim that all the phyla appearred in the Cambrian explosion.  They ignore more recent evidence that shows many phyla of life had their origins in the Precambrian.  One claim made in another post says there are no undisputed fossils found from the Precambrian.  What nonsense!  Let's look at some of the Precambrian fossils:
Kimberella
"Kimberella quadrata was originally described from late Precambrian rocks of southern Australia. It is also found on the White Sea, in the Ust’ Pinega Formation, mostly in member 9, where is occurs across several facies, throughout the section. Here it is found associated with channels in a clay substrate, associated with Tribrachidium, Dickinsonia, meandering trace fossils, and small algae.

"Reconstructed as a jellyfish, it was later assigned to the cubozoans (‘box jellies’), and has been cited as a clear instance of an extant animal lineage present before the Cambrian. Until recently, Kimberella was known only from Australia, with the exception of some questionable north Indian specimens. We now have over thirty-five specimens of this fossil from the Winter Coast of the White Sea in northern Russia. Our study of the new material does not support a cnidarian affinity. We reconstruct Kimberella as a bilaterally symmetrical, benthic animal with a non-mineralized, univalved shell, resembling a mollusc in many respects. This is important evidence for the existence of large triploblastic metazoans in the Precambrian and indicates that the origin of the higher groups of protostomes lies well back in the Precambrian" (Fedonkin & Waggoner 1997, Abstract)."

Here we have possibly the forerunner of all bilateral animals and an ancestor of the mollusk.  It's also interesting to note that 35 specimens, from the Precambrian, have been found.  These are undisputed fossils, all the experts agree that all 35 of them are really fossils of living animals.  And that's only one example.

Here's another:
Spriggina
"Reanalysis of Spriggina demonstrates the presence of genal spines (comparable to those of fallotaspidoid and paradoxidid trilobites), a cephalic region homologous to the effaced cephalons of agraulid and skehanid trilobites, and a dual cephalic region (also seen in Parvancorina) that compares to the parts of a trilobite cephalon anterior and posterior of the facial suture. Spriggina is thus a trilobitoid ecdysozoan, a conclusion in accord with Sven Jorgen Birket-Smith’s inference of an arthropod affinity for Spriggina. This result is among the first confident phylogenetic linkages between an Ediacaran and a Cambrian animal, and thus helps to demonstrate that Paleozoic animals could indeed be descended from Ediacarans."

A Precambrian ancestor of the trilobite!  As we can see, the creationist claim is without merit.  The Cambrian explosion is giving way to a slow burn fueled by complex organisms appearring in the Precambrian.

Other evidence besides recently discovered fossils also invalidates creationist claims of life appearring fully formed in the Cambrian.
The genetic evidence is also supporting complex life in the Precambrian, from here:
MolecularEvidence

"A literal reading of the fossil record suggests that the animal phyla diverged in an "explosion" near the beginning of the Cambrian period. Calibrated rates of molecular sequence divergence were used to test this hypothesis. Seven independent data sets suggest that invertebrates diverged from chordates about a billion years ago, about twice as long ago as the Cambrian."

Molecular, genetic evidence that life was evolving a billion years ago, deep in the Precambrian.

As to the oldest undisputed fossils, we have solid, unrefuted evidence of life going back 3.5 billion years, from here:
FossilBacteria

"It may seem surprising that bacteria can leave fossils at all. However, one particular group of bacteria, the cyanobacteria or "blue-green algae," have left a fossil record that extends far back into the Precambrian - the oldest cyanobacteria-like fossils known are nearly 3.5 billion years old, among the oldest fossils currently known. Cyanobacteria are larger than most bacteria, and may secrete a thick cell wall. More importantly, cyanobacteria may form large layered structures, called stromatolites (if more or less dome-shaped) or oncolites (if round). These structures form as a mat of cyanobacteria grows in an aquatic environment, trapping sediment and sometimes secreting calcium carbonate. When sectioned very thinly, fossil stromatolites may be found to contain exquisitely preserved fossil cyanobacteria and algae."

So we have excellent evidence of the first life forms from the Precambrian, from about 3.5 billion years ago.  And we have evidence of more complex life forms evolving in the Precambrian, with more being found every day.  Incorrect creationist claims should be laid to rest but everyone knows how they willfully ignore the evidence and continue to use refuted arguments.  Let's see how they react to these facts.


 


Posts: 1664 | Posted: 03:08 AM on October 18, 2007 | IP
orion

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Demon - excellent explanation!

I might add that while it is still uncertain what caused the relatively abrupt appearrance of larger, skeletonal and shelly life to appear during the Cambrian period, it was most likely  due to some critical threshold being crossed.  For instance, perhaps the level of oxygen reached a point that allowed increased metabolism leading to larger size and hard body structures.  It is almost certain that the major phyla of organism were already present at the beginning of the Cambrian period.  The scarcity of these fossils is merely due to the fact that these precambrian animals were soft bodied creatures.  But scientists are indeed finding more and more bilateral fossils of these soft bodied creatures.

Some of these were discovered recently in the Guizhou Province, China.  But soft-bodied animals do not leave their remains behind easily.  It requires a special mineralization process that occurs in rare strata known as lagerstatten deposits.  It was in one of these deposits that the famous Archaeopteryx fossils were found.  The Burgess Shale, an older deposit in British Columbia, is another example of a lagerstatten deposit.

See an article by Dr. David Bottjer - 'The Early Evolution of Animals' - Scientific American, Aug, 2005.
 


Posts: 1460 | Posted: 1:26 PM on October 18, 2007 | IP
    
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