Microfossils stromatolites

The time period in which prebiotic synthesis of organic compounds took place is frequently misunderstood. The earth is 4.5 x 109 years old, and the earliest fossil organisms known, the Warrawoona microfossils and stromatolites, are 3.5 x 109 years old.10 The difference is 1.0 x 109 years, but the time available for life to arise was probably shorter. It probably took a few hundred million years for organisms to evolve to the level of those found in the Warrawoona formation. In addition, if the earth completely melted during its formation, then the time available would be further shortened by the time needed for the earth to cool down sufficiently for organic compounds to be stable. 

Simonson B. M. and Lanier W. P. (1987) Early silica cementation and microfossil preservation in cavities in iron-formation stromatolites. Early Proterozoic of Canada. In Precambrian Iron-formations (eds. A. Uitterdijk, W. Peter, and L. L. Gene). Theophrastus Publ. and Pty. Co., Athens, Greece, pp. 187-213. 

Byerly et al. (1986) described probable stromatolites in the Fig Tree Group, preserved in grey-black finely laminated chert. The structures are made primarily of microcrystalline chert, forming low-relief laterally linked domes and in places pseudo-columnar structures. Byerly et al. did not find evidence of microfossils but inferred an organic origin from the morphology of the stmctures. However, Lowe (1994) disputed this evidence and concluded that the structures were not demonstrably of biotic origin. 

Awramik, S.M., 1976. Gunflint stromatolites microfossil distribution in relation to stromatolite morphology. In M.R. Walter (Editor), Stromatolites. Elsevier, Amsterdam, pp. 311—320. 

Walter, M.R., Goode, A.D.T. and Hall, W.D.M., 1976. Microfossils from a newly discovered Precambrian stromatolitic iron formation in Western Australia. Nature, 261 221—223. 

Late Archaean stromatolites Younger stromatolites have been described from 3.0 Ga rocks at Steep Rock in Canada (Wilks St Nisbet, 1985), from the 2.7 Ga Cheshire formation of the Belingwe Greenstone belt (Martin et al., 1980) and from 2.52 Ga shelf carbonate sediments in the Campbellrand subgroup, South Africa. In this latter locality there are also well-documented calcified microfossils of cyanobacteria (Kazmierczak St Altermann, 2002). It is also possible that at this locality the mineralization of the dead bacteria was the result of the action of het-erotrophic bacteria. 

Figure 12-4 will now be discussed in more detail. The record of reduced carbon in sedimentary rocks and the associated, 3C/I2C isotope shift date back to the oldest deposits of 3.5 Gyr ago, and even further if one makes allowance for the metamorphic alterations of the still older Isua formation (see Fig. 11-2). The biological origin of the isotope shift has been convincingly demonstrated, as reviewed by Schidlowski et al (1983). The implication that life had been in full swing 3.5 billion yr ago is supported by several lines of fossil evidence stromatolites, microfossils, and banded iron formations.

Buick R (1991) Microfossil recognition in Archean rocks an appraisal of spheroids and filaments from a 3000 M.Y. old chert-barite unit at North Pole, Western Austrdia. Palaios 5 441-459 Buick R (1992) The antiquity of oxygenic photosynthesis Evidence from stromatolites in sulphate-deficient Archaean lakes. Science 255 74-77... 

ONVERWACHT SOUTH AFRICA MICROFOSSILS "FIG TREE"-----------------STROMATOLITES... 

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