Posted by: paulgarner | November 6, 2010

Attenborough’s First Life

Friday evening saw part one of David Attenborough’s First Life programme broadcast on BBC2. It took a look at the early history of animals from an evolutionary perspective, from the rise of multicellularity to the origin of complex metazoans. As you’d expect, there was some beautiful photography as well as some gorgeous digital reconstructions of fossil organisms.

The programme focused upon the Neoproterozoic fossil record, conventionally dated between 1,000 and 542 million years ago. The middle part of the Neoproterozoic – the Cryogenian – is thought to have been a time of global glaciation, with ice sheets extending into the tropics. This was illustrated in the programme by a visit to eastern Canada, where diamictites containing ‘dropstones’ were said to be evidence of ancient ice sheets. Then in the latter part of the Neoproterozoic – the Ediacaran – the first animals make their appearance. The viewer was shown remarkable and exquisite fossil animals from the Charnwood Forest in Leicestershire, Mistaken Point in Newfoundland, and the Ediacara Hills of southern Australia. What follows isn’t a critical review of the programme, just a few thoughts that may help to place this part of the fossil record into a creationist context.

First of all, what about that global glaciation? As the programme pointed out, ‘dropstone’-bearing sediments of Neoproterozoic age have been found all over the world, even at equatorial palaeolatitudes. This has led geologists to develop the ‘snowball earth’ theory, which suggests that ice sheets covered all, or nearly all, the earth’s surface around 650 million years ago. But are these rocks really glacial in origin? Before the ‘snowball earth’ theory was developed, some geologists (e.g. Schermerhorn 1974) interpreted these rocks as catastrophic submarine slides, rather than glaciomarine indicators. Creationists tend to think the non-glacial interpretation was correct. For example, Sigler and Wingerden (1998) and Austin and Wise (1999) have argued that the diamictites of the Kingston Peak Formation, often interpreted as glacial in origin, are in fact debris flow deposits associated with the collapse of the continental margins at the beginning of the Flood. Diamictites of equivalent age are found at many locations around the world, and creationists think they have been mistakenly interpreted as the product of glaciation.

Stratigraphically above these diamictites, the first animal fossils make their appearance. They take the form of enigmatic segmented, disc-like or frond-like organisms now known as the Ediacaran fauna after the locality in South Australia where they were first discovered in 1946. How do creationists understand these strange and unfamiliar fossils? Kurt Wise has interpreted them as the inhabitants of a deep-water, sandy environment that was located on the pre-Flood continental shelf, one of a series of marine ecosystems buried and preserved near the beginning of the Flood (Wise 2003). Evidences of rapid burial often accompany these extraordinary fossils, as the programme made clear. For instance, the delicate organisms fossilized at Mistaken Point in Newfoundland occur within a deep-water turbidite sequence and were preserved by being buried in fine volcanic ash (Wood et al. 2003).

Part two of the programme will look at the Cambrian explosion and the animals of the Lower Palaeozoic.

References

Austin S. A., Wise K. P. 1999. Gigantic megaclasts within the Kingston Peak Formation (Upper Precambrian, Pahrump Group), southeastern California: evidence for basin margin collapse. Geological Society of America Abstracts With Programs 31(7):A455.

Schermerhorn L. J. G. 1974. Late Precambrian mixtites: glacial and/or nonglacial? American Journal of Science 274:673-824.

Sigler R., Wingerden V. 1998. Submarine flow and slide deposits in the Kingston Peak Formation, Kingston Range, Mojave Desert, California: evidence for catastrophic initiation of Noah’s Flood. In: Walsh R.E. (editor), Proceedings of the Fourth International Conference on Creationism, Creation Science Fellowship, Pittsburgh, PA, pp.487-501.

Wise K. P. 2003. The hydrothermal biome: a pre-Flood environment. In: Ivey R.L. (editor), Proceedings of the Fifth International Conference on Creationism, Creation Science Fellowship, Pittsburgh, PA, pp.359-370.

Wood D. A., Dalrymple R. W., Narbonne G. M., Gehling J. G., Clapham M. E. 2003. Paleoenvironmental analysis of the late Neoproterozoic Mistaken Point and Trepassey formations, southeastern Newfoundland. Canadian Journal of Earth Sciences 40(10):1375-1391.

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