Isua, sedimentary rocks

The age of meteorites tells us that the solar system - and therefore the Earth - was born roughly 4.6 billion years ago. The oldest terrestrial rocks are zircone crystals (zirconium silicates) which are 4.2 billion years old, but these stones do not tell us much apart from their age, because they are igneous, or magmatic, rocks whose melting processes have erased any trace of history. Much more interesting are the sedimentary rocks, because these were formed by materials that sank to the bottom of ancient seas, and may still contain remnants of the past. The oldest sediments have been found at Isua, in Greenland, and are 3.8 billion years old, which means that there were immense streches of water on our planet at that time, and that the first oceans had originated many millions of years earlier. 

Oldest preserved supracrustal rocks, Isua greenstone belt stratigraphy includes quartz-rich sedimentary rocks... 

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.

The oldest known sedimentary rocks are 3.8 Ga in age (4). They are at Isua, 120 km NE of Nuuk, western Greenland, adjacent to the retreating Greenland ice sheet (Figure 1). Sedimentary rocks outcrop in a narrow, hook-shaped belt 35-... 

Domain I, located in the NE of the greenstone belt was identified as a low-strain domain by Appel et al. (1998). This domain is dominated by mafic volcanic rocks, cherts and banded iron formation, and contains well-preserved, primary igneous and sedimentary features. Measured isotopic ages are between 3742 49Ma (Sm-Nd whole-rock, chloritic schists) and 3697 70 Ma (Pb-Pb whole-rock, banded iron formation) (Moorbath Kamber 1998 Frei et al, 1999). Moorbath Kamber (1998) suggested that their Sm-Nd isochron may represent the depositional age of this part of the Isua succession, whereas Frei et al. (1999) proposed that their Pb-Pb... 

Fedo, C. M., Myers, J. S. Appel, P. W. U. 2001. Depositional setting and palaeogeographic implications of earth s oldest supracrustal rocks, the >3.7Ga Isua Greenstone Belt, west Greenland. Sedimentary Geology, 141/142, 61-77. 

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