Plate tectonics fingerprint vanished 2.5 billion years ago in Earth crust shift

A chemical fingerprint embedded in ancient rocks from around the world has provided researchers with new clues about how and when modern geological processes began on Earth. Investigators at Curtin University analyzed thousands of rock samples spanning almost four billion years of planetary history and found a distinct signature that consistently appeared in materials older than 2.5 billion years before abruptly vanishing from the geological record.

The study, titled “Loss of ancient crustal reservoirs marks a shift in Earth's geodynamic regime,” was published in Proceedings of the Royal Society A. According to the authors, this vanishing fingerprint offers the clearest geological timing yet for when the processes shaping the planet's surface began to resemble contemporary plate tectonics.

Plate tectonics shapes continents and oceans while regulating the atmosphere and climate over deep time. However, determining when the mechanism started has long challenged geologists because the recycling of crust deep inside the planet destroys much of its own historical evidence. While previous mineral crystal studies suggested earlier beginnings for tectonic motion, the research team focused on a specific signature left behind when new crust forms by melting older rock.

Tracing the Vanishing Geological Signature

“We found it consistently in rocks older than 2.5 billion years,” said lead author Janne Liebmann, a research fellow at Curtin University's Timescales of Mineral Systems Group. She noted that the signature demonstrated how those rocks originated from a pool of ancient crust formed roughly four billion years ago. “Despite examining thousands of rocks, we never see it again,” she added, explaining that the disappearance points to a basic modification in how Earth's crust was built and transformed.

Co-author Chris Kirkland, a professor in Curtin University's School of Earth and Planetary Sciences, described the transformation as a transition from an early planet where ancient crust was repeatedly melted and reworked in place to a dynamic system capable of moving and recycling crust on a much wider scale. Kirkland noted that seeing the old fingerprint vanish at such a precise point in time marks the modern “tectonic engine” switching on, distinguishing Earth from inactive bodies such as Venus and Mars.