I have several tidbits from the Cambrian/Precambrian boundary which those
who believe that life originated miraculously in the Cambrian need to
consider. The first is the geochemical evidence of a world populated by
sponges in the Vendian--the latest period of the Precambrian.
"Petroleums and bitumens from Early Proterozoic (~1800 Ma) to Miocene (~15
Ma) age marine strata contain 24-isopropylcholestanes, a novel group of C30
steroids. The abundance of these compounds, relative to
24-n-Propylcholestanes, varies with source rock age. Late Proterozoic
(Vendian) and Early Cambrian oils and/or bitumens from Siberia, the Urals,
Oman, Australia, and India have a high ratio of 24-isopropylcholestanes to
24-n-propylcholestanes (>= 1, while younger and older samples have a lower
ratio (<=0.4). Temporal changes in this parameter may reflect the relative
abundance of certain Porifera (sponges) and certain marine algae through
time."
Mark A. McCaffrey et al, "Paleoenvironmental Implications of Novel C30
Steranes in Precambrian to Cenozoic Age Petroleum and Bitumen," Geochemica
et Cosmochimica Acta 58(1994):529-532, p. 529
David Campbell had alerted me to this article but it took me a while to find
it. It is a date from the White Sea which shows that the earliest mollusc
precursor, Kimberella, is 555 million years old.
"This provides a minimum age for the oldest definitive triploblastic
bilaterian, Kimberella, and the oldest well-developed trace fossils; and it
documents that spectacularly diverse and preserved Ediacaran fossils formed
more than 12 million years before the base of the Cambrian. The oldest known
bilaterian fossil, Kimberella, is only known from South Australia and the
White Sea. Kimberella, is an oval- to pear-shaped bilaterally symemetric
fossil that ranges from 0.3 to 14 cm long and has several zones arranged
concentrically with both soft and firm body parts. Fedonkin and Waggoner
interpreted Kimberella as being more complex than a flatworm and having
possible molluscan synapomorphies, such as a broad muscular foot. Seilacher
proposed that the radula scratches found in rocks of similar antiquity and
lithology in South Australia were made by a bilaterian (possibly Kimberella)
during pendulum grazing, which is also a molluscan feature. Radula scratches
now found with Kimberella below the dated ash at Zimnie Gory support this
interpretation. However whether Kimberella at 555 Ma indicates that the
protostome-deuterostome split is even older is not yet resolvable. Finally,
our age determination places such characteristic late Neoproterozoic guide
genera as Charnia, Dickinsonia, Tribrachidium and Kimberella at least 6
million years before the Namibian assemblage (549-543 Ma)." M. W. Martin, D.
V. Grazhdankin, S. A. Bowring, D. A. D. Evans, M. A. Fedonkin and J. L.
Kirschvink, "Age of Neoproterozoic Bilaterian Body and Trace Fossils, White
Sea, Russia: Implications for Metazoan Evolution," Science,
288(2000):841-845, p. 844
The above changes the chart I published on this list a few days ago which
can be found at
http://www.flash.net/~mortongr/cambchron.htm
Finally, how many 'explosions' have there been. Everyone focuses on the
Cambrian explosion but it really doesn't explain what is seen in the marine
fossil record. I would point you however to a chart in J. John Sepkoski, Jr,
"A factor Analytic Description of the Phanerozoic Marine Fossil Record,"
Paleobiology 7(1981):1:36-53, p 49. Here are the approximate numbers taken
from that chart.
Cambrian beginning 30 families
Cambrian end 175 families
Ordovician end 420 families (I don't hear people talking about an Ordovician
explosion)
Silurian end 450 families
Devonian end 400 families
Carboniferous end 425 families
Permian before extinct. 375 families
Permian very end 225 families
Triassic mid 320 families
Triassic end 240 families
Jurassic end 475 families
Cretaceous end 600 families
Today 1750 families
Most of the Cambrian explosion involved families that were essentially
extinct by the mid Devonian. About 90% of the families were from the
Trilobita, Polychaeta, Monoplacophora, and Inarticulata(Group I). All other
groups were very minor in the Cambrian. The Ordovician saw an entirely new
set of families come on the scene and largely replace group 1. These were
the Articulata, Crinoidea, Ostracoda, Cephalopoda Anthozoa, Stenolaemata,
and Stelleroidea. These groups (Group II) constituted about 80 percent of
the fauna from the Devonian to the Permian extinction. Then after the
Permian a third group came into play replacing the second group. These are
the Gastropoda, Bivalvia, Osteichtheyes, Malacostraca, Echinodea,
Gymnolaemata, Demospongia, and Chondrichthyes (Group III) This group
constituted about 70% of all families in the Mesozoic and most of the
Tertiary. Today there are 1750 families in the oceans and 2/3 of them have
no fossil record so we may be in the throws of another explosion. So there
have been 3 or 4 different 'explosions' not one. Once again, Christian
apologists have not kept up with the literature--and this is one from 1981.
Nor have they incorporated the differing proportions of animals which have
changed throughout time. Once again, I would ask, why don't we hear of such
things in our christian apologetical books?
glenn
Foundation, Fall and Flood
Adam, Apes and Anthropology
http://www.flash.net/~mortongr/dmd.htm
Lots of information on creation/evolution
This archive was generated by hypermail 2b29 : Sat Jun 03 2000 - 17:46:35 EDT