Counter arguments on the cambrian explosion.?

The main scientifically credible counterargument I have seen comes from genetic studies. Based on estimated mutation rates, the timing of divergence of the different phyla can be estimated. The estimates I think are quite rough, but suggests most of the major phyla had separated from each other well before the beginning of the Cambrian.

One number that springs to mind (which I may or may not have correctly remembered) is that the split between the lineages leading to vertebrates and echinoderms (one of the most closely related invertebrate groups) happened ~ 1.4 billion years ago.

I think there is also now an improved understanding of the late Precambrian Ediacara fauna (and related faunas) and that it contains precursors of many of the groups seen in the Cambrian - i.e. the groups in the Cambrian didn't just explode out of nowhere, but that the precursors were soft bodied, so much less commonly preserved and probably restricted to cold polar waters. The greatly increased fossil record in the Cambrian is in part probably due to increased availability of free oxygen. More oxygen opens up warmer water marine environments (where oxygen is less soluble in water) and provides extra metabolic energy such that for the first time many organisms had sufficient surplus energy to form hard parts, thus there is a big jump in preservation potential and wider distribution of organisms. In effect, the Cambrian explosion is in part a preservational artifact.

So while there was rapid diversification in the Cambrian, there was probably a long slow burn through the latter part of the Precambrian leading up to that diversification.

Precambrian fossils are quite difficult to describe and even more difficult to summarise. This is not helped by their relative infrequency and, commonly, their poor state of preservation. Beyond the Precambrian – Cambrian boundary, however, there was a sudden explosion in palaeo-zoological activity; this is often known as the ‘Cambrian Explosion’. Here, in the earliest Cambrian sediments, sophisticated articulate brachiopods, inarticulate brachiopods, trilobites, lamellibranchs, gastropods and echinoderms can be found in abundance. Trilobites are used as lower Cambrian stratigraphic marker fossils whilst the uppermost Precambrian rocks have no stratigraphic marker fossils at all!

In terms of evolution, brachiopods should have already undergone significant progression in terms of the split into articulate and inarticulate forms. Likewise with the trilobites, where even by the early Cambrian, there were three distinct families represented in the fossil record; the Agnostida, the Redlichiida and the Ptychopariida. Where are the Precambrian ancestors of these creatures?

Various ideas have been put forward. It has been suggested that increasing oxygen levels were responsible for this very sudden radiation in life forms at the base of the Cambrian. But why should that be so? Aren’t there iron oxide rich Proterozoic (i.e. Late Precambrian) sedimentary rocks? Besides, there is the need to explain the sudden rise in calcium carbonate uptake by the Lower Cambrian shelled fauna and for this, no satisfactory explanation has been offered.

What we find are ‘shots in the dark’. We find that evolutionary palaeontologists offer suggestions as to why the Cambrian Explosion happened without providing any evidence that these things actually occurred. Personally, I don't know what happened but I cannot accept a Darwinian Evolutionist explanation for the sudden emergence of complex life forms when there are no similar, slightly less developed forms on the other side of the Precambrian – Cambrian boundary.

Charles Darwin, 150 years ago, recognised this problem in ‘The Origin of Species’. He considered it an enigma that no fossil ancestors of the abundant Cambrian fauna had been found. He assumed that further palaeontological research / fossil hunting would reveal these ancestors. With 150 years having now passed, isn’t it time for the scientific world to be honest enough to state that no satisfactory scientific explanation can be found to explain the sudden rise in these preserved invertebrate fossils that is otherwise known as the Cambrian Explosion??

Counter to what? As typical to "great scientific mysteries" there are many ideas. Wikipedia does a reasonable good job. For the Intelligent Design position, Stephen C. Meyer's book, Darwin's Doubt, covers it well.

there are none