Scientists Discover Cosmic Clock in Zircon Crystals That Tracks Earth’s Landscape History

A "cosmic clock" has been discovered in tiny zircon crystals by scientists that can measure the formation and erosion of landscapes in Australia over millions of years. Cosmic rays, which are charged particles from space, constantly bombard the Earth's surface, producing isotopes. The scientists calculated the time each sand grain spent on the surface by vaporising the grains and analysing the amount of cosmogenic krypton gas trapped in them.

Reading Earth's cosmic clock

According to a press release, cosmic rays continually strike Earth, creating isotopes in surface rocks. Most decay too quickly to date ancient terrain. Krypton is different: it's a stable noble gas that accumulates in zircon crystals over millions of years. The team drilled cores in southern Australia's Nullarbor Plain to collect beach sands rich in zircon. Using a laser, they vaporised the crystals and measured the krypton released. Crystals with more krypton had spent longer at the surface.

A stable ancient landscape

About 40 million years ago, the landscape in southern Australia was transformed very slowly. Erosion rates were less than one meter per million years – this is comparable to the rates in the driest deserts in the world today. Beach sands high in zircon took about 1.6 million years to migrate from their source to the coast, where they were buried.

During this long process of erosion, the less complicated minerals were stripped away, leaving only the most resilient grains. Sea levels were high, and the earth was relatively tectonically quiet, so erosion rates remained low and allowed sediments to accumulate for millions of years. As Curtin geoscientist Milo Barham says, this "natural filtering" process concentrates hard minerals and is why Australia's beaches are so high in zircon and other heavy minerals.