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Acasta Gneiss Slave Lake Northwest Territories Canada
Acasta Gneiss is located in the remote Northwest Territories of northern Canada. The Slave Lake province is one of the oldest and most unique known zircon-bearing evolved crustal outcrops on our planet. The Acasta gneiss rock outcrop complex was formed during the earliest time of Earth's history, the Hadean Eon. The name is taken from the nearest location, the Acasta River, which is east of Great Slave Lake (some good distance north of Yellowknife). The rock exposed at this outcrop formed over 4 billion years ago. The age is based on radiometric dating of zircon crystals.
During the earliest part of the Hadean Eon the Earth’s surface was incredibly unstable. Deep convection currents in the Earth's mantle brought fiery, molten rocks to the surface and caused cooling rocks to descend into the magmatic seas. The heavier elements, like iron, descended to become the core and the lighter elements, such as silicon, became a part of the growing crust. It is unknown when the first outer crust of the planet formed, but it is thought that the existence of grains of zircon dated to about 4.4 billion years ago (Jack Hills Zircon) indicated the presence of liquid water and stable continents. The surface temperatures at that time were probably less than 212°F. Few rocks and minerals remain from the Hadean Eon because nearly all of this original crust has been subducted, either due to tectonic plate movements and other geological processes.
The oldest rocks known are the faux amphibolite volcanic deposits of the Nuvvuagittuq greenstone belt in Quebec, Canada which are estimated to be about 4.28 billion years old. The Jack Hills zircons, in Australia, are the oldest mineral grains so far found on Earth. They provide compelling evidence that have led scientists to believe that the atmosphere and oceans most likely formed before 4.4 billion years ago.
Size of Acasta Gneiss Specimen: 55mm L X 36mm W X 21mm D
Acasta Gneiss makes a great, important specimen for a geological collection.
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