Australia’s ancient environments – documented in Aboriginal songlines for millennia – now yield deeper secrets through an unexpected source: cosmic rays trapped within mineral crystals. A new study, published in Proceedings of the National Academy of Sciences, demonstrates how these “cosmic clocks” can reveal the evolution of landscapes, from river systems and coastlines to the formation of valuable mineral deposits.
Deep Time and Earth’s Ever-Changing Surface
Earth’s surface is a battlefield between erosion and uplift. Mountains rise, then crumble; coastlines advance, then retreat. Understanding how these processes played out over millions or billions of years is vital for predicting how landscapes will respond to future changes, such as climate shifts or sea-level fluctuations. Directly measuring ancient landscape evolution has been difficult — until now.
Researchers recovered samples from buried shorelines along Australia’s Nullarbor Plain, revealing a dramatic history. The area was once a seabed, later home to giant tree kangaroos and marsupial lions, and today stands as one of the flattest, driest places on Earth. These ancient beaches contain high concentrations of zircon, a mineral that acts as a remarkably stable time capsule.
The Cosmic Fingerprint: How it Works
Earth is constantly bombarded by cosmic rays – high-energy particles from exploding stars. When these rays collide with atoms in minerals near the surface, microscopic “explosions” create new elements called cosmogenic nuclides. Measuring these nuclides has long been used to estimate landscape change, but many decay too quickly for ancient timelines.
This study harnessed cosmogenic krypton stored inside zircon crystals. Krypton does not decay, preserving information for hundreds of millions of years. By vaporizing thousands of zircon grains with a laser and measuring the released krypton, scientists determined how long each crystal spent exposed at the surface before burial. The more krypton, the longer the exposure.
Australia’s Surprisingly Stable Past
Around 40 million years ago, southern Australia was warm, wet, and forested. Yet, landscapes eroded at an exceptionally slow rate – less than one meter per million years. This is slower than in dynamic mountain regions but comparable to some of Earth’s most stable environments today, like the Atacama Desert or Antarctica.
The study also tracked the movement of zircon-rich beach sands: a remarkably slow process taking approximately 1.6 million years from erosion to burial. This slow movement naturally filtered out less durable minerals, concentrating resilient zircon. The result? Economically valuable deposits that now feed into everyday ceramics.
The Future of Landscape Research
This “cosmic clock” offers a new way to understand the history of Earth’s surface. It explains the mineral wealth along the Nullarbor Plain, including the Jacinth-Ambrosia mine, which supplies roughly 25% of the global zircon market. By reading cosmic ray fingerprints in zircon, researchers have unlocked a geological tool for measuring ancient processes.
The technique can be refined by studying modern landscapes with independently measured surface processes, but its potential is vast. It can be applied to periods of Earth history hundreds of millions of years ago, potentially revealing how the rise of land plants reshaped the planet’s surface and atmosphere.
Earth’s landscapes hold memories in minerals formed by cosmic rays. By learning to read this “cosmic clock,” we gain a new understanding of the past — and a blueprint for the changes that may lie ahead.
