Greenstone belt in the Barberton Mountains

A mountain range in eastern South Africa contains crystals that date to the period when the planet’s first solid rock was forming. Credit: Gary Byerly

Geology

Extraordinary crystals hold secrets of Earth’s infancy

Mountains in South Africa’s Barberton region contain a rare hoard of minerals more than 3 billion years old.

Geologists have a new window onto the early Earth: zircon crystals from South Africa that could be as much as 4.1 billion years old.

Ancient crystals of zircon — a durable mineral found in rock that has been squeezed and heated — from Western Australia have revealed some of the planet’s early secrets, such as clues to the chemistry of its primordial crust. But researchers have had little in the way of other records for this period of Earth’s infancy. Now, Benjamin Byerly at Louisiana State University in Baton Rouge and his colleagues report their discovery of a second rich trove of zircons. The crystals lie east of Pretoria, in a rock formation known as the Barberton greenstone belt.

The African zircons are important because they have been subject to less heating and squeezing than the Australian samples. As a result, the African crystals may have richer stories to tell about the chemistry of Earth’s early years.

Scanning electron microscope images of Green Sandstone Bed zircons

Examples of the African zircons.Credit: Gary Byerly