Saturday, October 3, 2009

The Cambrian Explosion, the Discovery Institute, and Charles Doolittle Walcott

The Discovery Institute is back with another attempt to legitimize Intelligent Design, this time with a movie on the Cambrian Explosion - Darwin’s Dilemma.

I haven’t seen the film, but given the well documented problems the Discovery Institute and its cohorts seem to have with basic honesty, I’m expecting the usual snow job.

I intend to write a set of blog posts addressing the comments and thoughts on Darwin’s Dilemma from people who have seen the film. This is useful because people who do not have a background in the Cambrian Explosion or palaeontology are the people that the Discovery Institute is hoping to mislead. So what such people are taking away from the film, the messages that the Discovery Institute is hoping to instill, the questions raised in people’s minds, etc., are worth addressing.

This post is in response to Ian’s comments here, to address what appears to be a misleading section in the film regarding Charles Doolittle Walcott (the discoverer of the Burgess Shale) and alleged contemporary geological ideas as to the whereabouts, and lack, of Precambrian fossils.

Ian writes:
According to the movie Walcott (the discovered of the Burgess Shale) suggested that the transitional Precambrian fossils might be found beneath the ocean floor. I have no idea whether this was a serious prediction or not, but the movie treats it as if it were. They say that Walcott’s hypothesis remained untested until deep-water drilling for oil has brought lots of drill cores from the bottom of the ocean, and none have revealed Precambrian fossils. They then go on to say that ocean-floor mapping has revealed that the rocks of the ocean floor are relatively young, and the ocean floor is an entirely unsuitable place to look for Precambrian fossils.
So is this correct? Well, the first part is – but needs some clarification (surprised?), but the rest is pure bollocks.

Firstly did Walcott suggest that Precambrian fossils would be found beneath the ocean floor? Well, yes he did, but deep under the ocean, not necessarily deep under the ocean floor. This was in response to his being unable to find Precambrian fossils.
I have for the past 18 years watched the geological and paleontological evidence that might aid in solving the problem of Precambrian life. The great series of Cambrian and Precambrian strata in eastern North America from Alabama to Labrador in western North America from Nevada and California far into Alberta and British Columbia, and also China, have been studied and searched for evidences of life until the conclusion had gradually been forced upon one that on the North American continent we have no known Precambrian marine deposits containing traces of organic remains, . . . (Walcott 1910, p.2)
To explain this Walcott suggested that the Precambrian continents were much greater in extent than the present, or even the Cambrian, continents, and so the Precambrian ‘coastlines’ – and hence shallow water marine sediments to look for fossils – were much further out to sea compared with the current coastline. In other words, the current continents are the centres of the Precambrian continent and represent
. . a period of continental elevation and largely terrigenous sedimentation in non-marine bodies of water, also a period of deposition by aerial and stream processes over considerable areas (Walcott 1910, p.4)
Walcott hypothesized a much larger Precambrian continent to account for the lack of marine Precambrian sediments because he was working in a time before the theory of plate tectonics revolutionized our understanding of continental processes. In Walcott’s time the continents were considered stationary, and so a lack of sediments represented a period of uplift and wider continents, whereas the presence of marine sediments represented a period of subsidence and seas inundating the margins of the continents.

So Walcott considered that the margins of the Precambrian continent were much further out in the oceans that the present continental margin, and hence the shallow marine sediments with Precambrian fossils would be found under the deep ocean. This period of unknown marine sedimentation was named the Lipalian period. But Walcott’s hypothesis and the Lipalian period was short lived.

Which brings up to the second claim, that Walcott’s hypothesis remained untested until deep-water drilling for oil has brought lots of drill cores from the bottom of the ocean, and none have revealed Precambrian fossils.

Say what?!

Umm, Walcott’s hypothesis of the Lapilian period of non-deposition was largely ignored,
Despite Walcott's diligent search, hardly any fossils were found in these older strata, and those discovered did not assist in biostratigraphy. Years later, when attempting to explain the issue of a diverse Cambrian fauna seemingly without any antecedents, Walcott developed a hypothesis to explain the absence of earlier fossils based on geological, rather than biological, features. He suggested that a widespread unconformity at the top of the Proterozoic represented an interval oftime, the Lipalian, in which such an earlier fauna developed elsewhere, but was not recorded in any outcrop. The concept of naming a gap to represent a major missing segment of geologic time, did not result in any comment from the geologic community and the Lipalian Interval vanished. (Yochelson 2006)
Walcott was doing science. He had observations – apparent lack of marine Precambrian sediments – and produced a hypothesis to account for them. But the hypothesis was not taken up. It was, however, tested, albeit indirectly.

By the late 1950 and early 1960’s the theory of sea floor spreading was becoming well established and by the end of the 1960 it was shown that the ocean floor was younger than Precambrian through measuring the magnetic striping caused by magnetized lava formations (see for example Heirtzler 1968). See floor spreading and plate tectonics rendered any vestige of Walcott's hypothesis redundant.

So, far from waiting until deep sea coring (not incidentally related to oil exploration, but to the Joint Oceanographic Institutions for Deep Earth Sampling, Ocean Drilling program in the mid 1980’s), it has been well known that there are no Precambrian rocks awaiting discovery under the deep oceans for at least 40 years.

But the Discovery Institute film also neglects the fact that fossil-bearing marine Precambrian rock had been discovered before this: Charnwood Forest, England (Ford 1958); South Australia and Namibia (Glaessner 1959); and subsequently from Canada, Russia, and the USA.

To suggest that Walcott's hypothesis wasn't tested, or that palaeontologists were somehow hanging out for deep sea cores to provide Precambrian fossils, is laughable, but this is the Discovery Institute.

Ford T.D. (1958) Precambrian fossils from Charnwood Forest. Proceedings of the Yorkshire Geological Society. 31. p.211-217

Glaessner, M (1959) Precambrian Coelenterata from Australia, Africa and England. Nature. 183. p.1472-1473.

Heirtzler, J.R. Sea Floor Spreading. Scientific American, December 1968, p.60-70.

Walcott, C.D. (1910) Abrupt appearance of the Cambrian fauna on the North American Continent. Cambrian Geology and Paleontology II. Smithsonian Miscellaneous Collections 57. p.1-16.

Yochelson, E.L. (2006) The Lipalian interval: A forgotten, novel concept in the geologic column. Earth Science History. 26(2), p.251-269.

No comments:

Post a Comment