Canadian Rockhound: Archean Butterstone

Archean Butterstone
By Clive Knell, Florence, SC

This rock is from the Greenstone Belt of southern Africa, which was formed during the Archean Period and is over 2500 million years old. The Archean Period covers 45% of the earth's history-from the beginnings of the planets (about 4500 million years ago), up to the beginning of the Proterozoic Era (2500 million years ago).

Formation

During the Archean Period the surface of the earth formed, the oceans and the continents were established and life began in the shallow sea environment. There must have been seabed outcrops or lakes of considerable size which were turbid and muddy. This residue would over time have precipitated to the bottom in layers and early algael life would have settled within these banded layers of muddy residue. Around 2800 million years ago the atmospheric pressure was higher and heat production around 3 times present heat production, due to increased volcanic activity. This led to the serpentinization (green color) of the sediments that had by now become hard.

Archean butterstone is very old rock, predating the dinosaurs
by over 2500 Million Years.

Micro Fossils

Micro fossils in the form of Stromatolites of blue green algae have been found in the fine laminations and may represent the beginnings of life on earth and contain a history of our own origins. Micro fossils are microscopic relics preserved in rock by being incorporated into the sediment in such a way that they are not immediately broken down but are replaced in fine detail by the fossilization process. Stromatolites are structures in the laminated sedimentary rocks built by organisms such as algae or bacteria that have precipitated carbonates from the surrounding waters. Micro fossils in the form of fossilized algae are the earliest known life forms, predating the dinosaurs by 2500 million years, and represent the beginnings of life and fossils as we know them. Unlike conventional fossil collecting, the search for micro-organisms proves to be more difficult as Archean rocks do not give up their secrets easily. Identification of the microorganisms is difficult due to the lack of fine detail. There is, however, almost certain evidence of early life from about 2700 million years ago, with evidence of early life in southern Africa dated at about 3500 million years by Hamilton et al in 1979.

Archean Butterstone Carving
Carving made from archean butterstone.

It is quite probable that the appearances of the rocks found today do not resemble the early Archean shallow water crater environments, which have been lost over time. One can only speculate that in late Archean time, the earth's shallow water environment may have been widely populated by Cyanobacteria (blue-green algae). Perhaps the entire waterways were populated by a diverse population of Procaryotes.

Whatever the controversy, it is a humbling experience to hold a piece of ancient history of such an incredible age in your hands, contemplate its formations and wonder at its origins.

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