Digging Down to the Beginnings of Plate Tectonics

A discovery in South Africa has provided the oldest evidence yet of subduction, a fundamental process of plate tectonics. Researchers analyzing zircon crystals, some dating back 4.15 billion years, found geochemical signatures pointing to a major transition around 3.8 billion years ago—from a stable, unmoving crust to the dynamic system of shifting plates we see today.

Earth’s crust and upper mantle are divided into rigid plates that slowly move atop the more fluid rock below, driven by heat from the planet’s core. This motion shapes our world, fueling earthquakes, volcanoes, and mountain formation. However, the question of when plate tectonics first began has long remained unresolved, with estimates ranging from over 4 billion to just 800 million years ago.

In their 2022 study, published in the journal AGU Advances, researchers examined hafnium isotopes and trace elements within zircon crystals from the Barberton Greenstone Belt, a rare remnant of ancient crust. Their findings suggest that around 3.8 billion years ago, Earth’s crust began experiencing pressures and melting conditions similar to modern subduction zones, where one plate dives beneath another. This marks one of the earliest known instances of plate movement, similar to today’s Andes mountain range or the Pacific’s Ring of Fire.

Prior to this shift, older zircons indicated a stable “protocrust” that had remained largely unchanged for 600 million years. However, similar transitions were observed in zircons from other global locations, hinting at a widespread reorganization of Earth’s crust. If confirmed, this could mark the true beginning of plate tectonics as a planetary process.

Beyond shaping the surface, plate tectonics plays a key role in regulating Earth’s climate. Volcanic activity and crust formation help control atmospheric carbon dioxide levels, preventing extreme swings between boiling hot and freezing conditions. This geological thermostat may also be essential for making a planet habitable, raising intriguing questions about the importance of plate tectonics in the development of life, not only on Earth, but also on extraterrestrial planets.