4100 – 4000 million years ago

Year six

The oldest rocks

Acaster Gneiss
Acaster Gneiss

The oldest rocks are around 4000 million years old, but there is no evidence of life from this time.

The oldest rock in the world is almost 4000 million years old. It is called the Acaster gneiss, after the place on Old Rock Island, Slave Province, Canada, where it is found.

A gneiss (pronounced 'nice') is a metamorphic rock; in other words it is a 'changed' rock. Metamorphic rocks form deep underground where the intense pressures and high temperatures cause changes to take place. The pressure and temperature deep in the Earth's crust cause new minerals to form and the resulting rock is very different from the original one.

Gneiss looks a little like granite, but because they have been squeezed under high pressure, the crystals of quartz, feldspar and mica are very often arranged in layers.

There is no evidence of life at Acaster, but this is not surprising because any fossils that might have been present in the original rocks would have been totally destroyed by metamorphism when the gneiss formed.


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