Apex chert

Fig. 10.2 Cyanobacteria-like, filamentous carbonaceous fossils from the 3.456-billion-year-old Apex chert in northwestern Australia their origin and formation are still under discussion. The photographs are accompanied by the corresponding drawings.

The best sealed-in minerals are zircons, zirconium silicate minerals which are formed when melted lava on the flanks of volcanoes solidifies. When the zircons crystallize out, they incorporate radioactive uranium (in particular 238U), which decays in several steps, leading Anally to the lead isotope 208Pb. The rate of decay is very low, as the half-life of uranium-238 is 4.5 x 109 years. Thus, the U-Pb-zircon method for age determination of Precambrian rock is very important. The fossils studied by Schopf were sandwiched between two lava layers (Schopf, 1999). The volcanic layers were dated to 3.458 0.0019 x 109 years and 3.471 0.005 x 109 years the age of the fossil layer (Apex chert) was thus determined to be about 3.465xlO9 years. 

Fig. 10.4 Fossilized cellular filamentous microorganisms (two examples of Primaevifilum amoenum). They are 3.456 billion years old and come from the Apex chert region in northwestern Australia. As well as the original images, drawings and the Raman spectra and Raman images, which indicate that the fossils have a carbonaceous (organic) composition, are shown. With kind permission of J. W. Schopf...

Apex chert (Western Australia), -3,465 Ma Pnmaeciftlum amoenum... 

Further studies are thus required to determine whether the Earth s oldest putative microfossil assemblages from the Apex chert represent genuine primeval life forms or only a fatal delusion (Schopf et al., 2002b Brasier et al., 2002b, 2004). 

Schopf JW (1993) Microfossils of the early Archean Apex Chert new evidence of the antiquity of life. Science 260 640-646... 

Life on Earth may have started between 3.5 and 3.9 billion years ago, as shown in Figure 3.2. The oldest microfossils were described by J. W. Schopf from the Apex Chert at Marble Bar, Western Australia (Schopf, 1992, 1993, 1998). These are dated at 3.465 Ga. Microfossils from Swaziland (South Africa) are of similar age. The North American Gunflint Chert (2 Ga) and the Belcher Group microfossils from Canada are the first occurrence of the Precambrian. ... 

Schopf J. W. (1983) Microfossils of the Early Archean Apex Chert new evidence for the antiquity of hfe. Science 260, 640-646. 

Critical testing of earth s oldest putative fossil assemblage from the 3.5 Ga Apex chert, Chinaman Creek, western Australia. Ptecambrian Res., 140, 55-102. 

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