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The oldest rocks on Earth

Oli Usher31 July 2014

A crystal of zircon (zirconium oxide). Credit: Denniss/Wikimedia Commons (CC-BY-SA 3.0)

A crystal of zircon (zirconium oxide). Credit: Denniss/Wikimedia Commons (CC-BY-SA 3.0)

The Earth is about 4.5 billion years old, but almost everything on its surface is much, much younger. Mountain ranges are formed and erode, oceans rise and fall, and the tectonic plates of our planet’s crust are constantly being subducted and renewed.

But there are still some surprisingly old rocks on the surface of the Earth.

In the Jack Hills region of Australia, geologists have found small crystals of zircon that can be dated to about 4.4 billion years ago – a period in which the young Earth was totally different to how it is now (it even had a partially molten still). These tiny minerals have survived largely unchanged for almost the entire history of the Earth, despite the total renewal of the rest of our planet’s surface in that time.

The Namib Sand Sea, a desert in south-west Africa, is another case in which geologists find surprisingly old minerals: in this case, grains of sand which have been sitting in the desert for over a million years. By comparison, many far more solid-looking features of Northern European landscapes, such as the rugged terrain of the Scottish Highlands, are less than 20,000 years old, having formed in the last glaciation.

In this video, Dr Pieter Vermeesch (UCL Earth Sciences) explains how geologists in the London Geochronology Centre at UCL are able to use cosmic rays from distant supernovae to calculate the age of the sand in the Namib Sand Sea.

Update – 06.08.14 – The Department of Earth Sciences has just published three further videos featuring Pieter Vermeesch talking about geochronology.