Researchers have developed a novel "cosmic clock" technique utilizing cosmogenic krypton within zircon minerals to reconstruct the evolution of ancient landscapes over tens to hundreds of millions of years. This method offers insights into historical erosion rates, sediment transport, and the formation of significant mineral deposits, particularly in southern Australia. The findings contribute to understanding how Earth's surface responds to geological processes and climate change.
The Cosmic Clock Technique
The new technique centers on analyzing cosmogenic krypton trapped within tiny, resilient zircon crystals. Cosmic rays, high-energy particles from space, constantly bombard Earth. When these rays strike atoms in minerals near the surface, they create new elements known as cosmogenic nuclides. Unlike other short-lived nuclides, cosmogenic krypton stored in zircon crystals does not decay, allowing it to preserve information for millions of years.
To apply this method, researchers use a laser to vaporize thousands of zircon crystals and measure the amount of krypton released. The quantity of krypton indicates the duration a zircon grain was exposed near the Earth's surface before being buried by sediment layers. This measurement acts as a "cosmic clock," revealing how quickly or slowly ancient landscapes eroded and shifted over vast periods. An international team, including researchers from Curtin University, the University of Göttingen, and the University of Cologne, pioneered this development.
Uncovering Australia's Ancient Landscapes
The study examined samples from southern Australia, including ancient beaches of the Nullarbor Plain, which are now situated over 100 kilometers inland. These buried shorelines document significant landscape transformations, evolving from a former seabed to a woodland and eventually one of the driest regions on Earth.
Key findings from the research indicate that approximately 40 million years ago, southern Australian landscapes eroded at an extremely slow rate, less than one meter per million years. This rate is considerably slower than in mountainous regions but comparable to stable areas like the Atacama Desert. The study also determined that zircon-rich beach sands took about 1.6 million years to move from their point of erosion to final burial on the coast.
Researchers observed that when landscapes are tectonically stable and sea levels remain high, erosion significantly slows, allowing sediments to be stored and reworked near the surface for millions of years. This period of stability was followed by a turning point where shifting climate, Earth movements, and sea level changes triggered faster erosion and sediment movement.
Implications for Mineral Resources and Future Research
The prolonged transport and storage of sediments play a crucial role in concentrating durable minerals. As less stable materials erode during extensive travel, resilient minerals like zircon become concentrated. This natural filtering process created beach sand deposits rich in economically valuable zircon and other stable minerals. For instance, the Jacinth-Ambrosia mine, which contributes approximately a quarter of the global zircon supply, is attributed to these geological processes. Understanding these connections is important given increasing demand for such minerals.
The "cosmic clock" technique allows for the measurement of ancient processes on Earth's surface, offering the capability to study periods hundreds of millions of years ago. This opens possibilities for investigating landscape responses to major historical events, such as the rise of land plants 500–400 million years ago. Analyzing zircon crystals preserved in ancient river sediments could quantify how the advent of land plants reshaped erosion, sediment transport, and landscape stability, providing a blueprint for understanding past and future landscape changes and their impact on resource availability and environmental management.