ARE STROMATOLITES
REALLY FOSSILS?
New findings from Precambrian rocks
For years, it has been customary to interpret Precambrian stromatolite structures (mounds) as the fossilised remains of communities of cyanobacteria and single-celled algae. Modern analogues have been found in a few places (such as Shark Bay in Australia) and the consensus became that the origin of stromatolites was biogenic. David Attenborough has some illustrations of both fossil and living structures in his Life on Earth. Earlier and earlier stromatolites have been found - going back to 3.5 billion years. This raised some questions in people's minds as to whether they are genuine fossils. It has emerged that there are no Archaean (Early Precambrian) stromatolites containing evidence of the microorganisms which are supposed to have constructed them. Also, that there is ample evidence of carbonate precipitation during the Precambrian which resulted in some very stromatolite-like structures.
A test of the biotic/abiotic models has recently been made, utilising stromatolites from sediments considered to be 1.9 billion years old. This summary is taken from Walter (1996):
"Using photographs taken in the field, and polished slabs of rock in
the laboratory, [the researchers] traced and digitised the layers of stromatolites
to allow the calculation of mathematical power spectra. They show that,
over three orders of magnitude in size, the stromatolite laminae as seen
in the field and on the slabs obey the same power law. From this they
obtain the fractal dimension of the stromatolites, and use it to deduce
the processes of stromatolite growth.
"The upshot, they propose, is that the morphogenesis of all stromatolites
can be accounted for by four abiotic processes: fallout of suspended sediment,
downslope movement of that sediment (or the mathematical equivalent surface-tension
effects in chemical precipitation), surface-normal precipitation, and
random effects.
They conclude that, theoretically, abiotic processes can generate stromatolites,
and in the absence of microfossils within them it may be impossible to
prove their biological origins."
"However, inasmuch as microorganisms exist in virtually all shallow marine environments today, it would be misleading to assume that they did not inhabit the surfaces of most, if not all, Precambrian stromatolites. But if they did, then it is no longer clear what role they played in morphogenesis."
The following observations and comments seem appropriate.
(a) The existence of stromatolite fossils has provided the evolutionary scenario
of origins with quite a bit to talk about in the Precambrian. For example,
Attenborough (1979) writes: "the arrival of the blue-greens [algae] marked
a point of no return in the history of life" (p.22). If the stromatolite mounds
cannot be used to portray the idea of colonisation of shallow seas in the
Precambrian, because they are abiogenic and not due to algal or bacterial
activity, the evolutionary stories about the way these organisms changed the
world during the Precambrian become even less convincing.
(b) There has been an influential group of geologists who have used stromatolites
as indicators of past environments. If the biogenic explanation is inappropriate,
then it opens the door for some radical ideas about the Precambrian palaeoenvironments.
(c) Abiotic stromatolites do not appear to be forming today. This suggests
that we ought to be much more open to the "unusual" when interpreting the
Precambrian.
The points made in (b) and (c) are of considerable significance to myself and several colleagues who are seeking to integrate the Precambrian rocks into our understanding of earth history and the effects of the Genesis Flood. We are developing an understanding of the Precambrian which involves devastation experienced during the early stages of the Flood: very high energies and extreme violence. The in situ growth of stromatolites does not readily fit into this model - and the abiotic interpretation could be regarded as one predicted by the larger scale model of Precambrian catastrophism.
These new findings cannot, of course, be regarded as a proof of the catastrophic model - but the door now appears to be wide open for some fresh thinking about the Precambrian and its significance for origins.
David J. Tyler (November 1996)
Additional note (December 2002)
At the GSA Denver Annual Meeting (October 27-30, 2002), some interesting perspectives on Precambrian stromatolites were expressed by James and Narbonne. The point out that: “Paleoproterozoic (2.5-1.6Ga) reefs were fractal in nature, constructed by stromatolites in which the influence of synsedimentary carbonate precipitation exceeded that of microbes and/or biofilms.” In the Early and Mid Precambrian, abiotic precipitation was extensive and widespread. There is a trend of increasing biological activity, although precipitate-dominated structures are still found in the Late Precambrian.
These findings connect well with the view expressed above that the devastation of the early stages of the Flood (the first 40 days) can be linked with the Early-Mid Precambrian, with no opportunity for any significant biological structures to be formed. Later, as the “destructive phase” moves into the “prevailing phase” of the Flood, there are opportunities for structures to be built involving a mixture of precipitation and microbial activity. Thereafter, the oceans show signs of recovery of its marine fauna: Ecosystems do not spring back overnight - they have to be rebuilt. The food chain must be restored. When we look at food chains in the seas, we find microplankton—plankton—invertebrates—fish—predators. This is the essentially the sequence we find in the Proterozoic, Cambrian, Ordovician, Silurian and Devonian strata. Our response to the evolutionist is that we witness an ecological succession in the rock record, not an evolutionary succession.
References:
Attenborough, D. 1979. Life on Earth. Collins & BBC, London.
Grotzinger, J.P. & Rothman, D.H. 1996. An abiotic model for stromatolite
morphogenesis, Nature, 383(3 October), 423-425.
Walter, M. 1996. Old fossils could be fractal frauds, Nature, 383(3
October), 385-386.
James, Noel P. and Narbonne, Guy M., Proterozoic reef evolution, Paper
No. 24-1, 2002 GSA Denver Annual Meeting (October 27-30, 2002)
