Scientists at Curtin University have developed a novel framework for dating the Earth’s evolution, including the formation of continents and mineral deposits. Their research, published in Earth Science Reviews, focused on Australia’s abundant lead-zinc ore deposits and utilized a comprehensive global database. The study identified a pivotal moment in Earth’s history approximately 3.2 billion years ago when the planet transitioned from a layered structure to a process of remixing, potentially driven by the emergence of global-scale plate tectonics—an ongoing phenomenon that continues to shape Earth today.
The lead researcher, Dr. Luc Doucet, who heads Curtin’s Earth Dynamics Research Group, explained that a key objective was to determine when the composition of the continental crust began to significantly diverge from that of the Earth’s mantle, which is the source of continental material. To address this question, the team needed to understand the evolution of the Earth’s mantle since the formation of the Moon around 4.5 billion years ago—a cataclysmic event caused by the collision of a massive asteroid with the proto-Earth that altered its core and mantle. The challenge involved reconciling this widely accepted theory with the composition of the present-day mantle.
To reconstruct the Earth’s mantle evolution, the researchers analyzed lead isotope compositions from rock samples spanning different locations and time periods. They examined various components of the Earth’s layers, including primitive meteorites formed at the same time as the solar system. These analyses enabled them to compare the evolution of the Earth’s mantle with that of the continental crust. Dr. Denis Fougerouse, a co-author from Curtin’s School of Earth and Planetary Sciences, noted that large lead-zinc deposits, which are known for tracking continental crust composition over time, played a crucial role in this comparison. Australia, with its abundant lead-zinc ore resources estimated at 52 billion metric tons, offered an ideal setting for the study. These deposits range in age from 3.4 billion years in Western Australia’s Pilbara region to relatively youthful deposits at 285 million years.
The team’s analysis revealed that significant differences between lead-zinc deposits and the Earth’s mantle began to emerge around 3.2 billion years ago. This period is believed to mark the onset of plate tectonics as the primary driver of continent formation on Earth. Interestingly, Earth is the only known planet in our solar system that exhibits plate tectonics, and it is also the only planet known to support life.
An additional outcome of this groundbreaking research is the need to calibrate radiometric ages for future dating of Earth’s evolution and mineralization events. The Curtin group established uranium-lead isotopic system curves, which will serve as a valuable tool in this calibration process.
Source: Curtin University