One of the evolutionary scientists' biggest assumptions is that the molecular clock is reliable.... When Levinton gave his paper [at the 1996 GSA meetings in New Orleans] he stated that the molecular clock can be best compared to a sun dial in the shade, which isnít very encouraging for his method, but he and his colleagues still believed that it yielded data sufficient to test the theory of the rapid evolution of life at the base of the Cambrian....
From their molecular clock data they concluded that the initial divergence of metazoan life forms occurred about 1.2 billion years ago (+/- 50 to 250 million years) . The base of the Cambrian is currently dated at about 543 million years ago , so their conclusions require a half billion years of metazoan history before the Cambrian. They also concluded that the beginning of Metazoan phyla was not an explosion, but was somewhat spread out during that half billion years.
A couple of days later these papers were discussed in a 'Hot topics discussion' during the noon hour. Four scientists gave brief presentations on the new ideas about the Cambrian explosion, followed by audience questions and comments. Many questions dealt with technicalities of their research method, but two questions stand out. A little background is necessary before dealing with these questions. The proposal that complex metazoan animals, ancestral to such things as molluscs, trilobites, vertebrates, sea urchins, corals, and many others, existed for a half billion years before the Cambrian implies that they lived all that time without leaving a fossil record. This pretty much requires that before the Cambrian they existed as soft worm- or larvae-like forms, with the general genetic make-up of the Cambrian groups but without their skeletonized morphology.
Now the questions. The first of the two questions was - why are trace fossils (fossil tracks, trails, and burrows) so rare before the base of the Cambrian, if these animals existed for that half billion years? An internationally recognized expert on trace fossils stood up, presumably to answer the question. However, he talked about other things and the very important question never was answered. At the end of the discussion another scientist stood up and commented on the implication that all the skeletonized phyla developed skeletons at about the same time in the Cambrian. He asked - why are all these types of animals living for so long and then all making skeletons all at once? He then asked, with some vigor - 'Why are you avoiding the real question?' After a pause, one member of the original presenters answered 'because itís really hard (a hard question)'. He went on to say that they hoped answers would come from further study of developmental biology.
These two questions were apparently not asked by people who doubted the evolution theory, but by evolutionary scientists willing to ask the hard questions that need to be addressed as they try to test between different hypotheses. The fact remains that the Cambrian explosion is one of the big challenges to naturalistic theories that still remains unanswered.
2010 Arthur V. Chadwick, Ph.D.