This revelation implies that the defining chemical composition of continents emerged right at the dawn of Earth's formation.
Leading the international team was Professor Emeritus Simon Turner from Macquarie University's Faculty of Science and Engineering, alongside colleagues from institutions in Australia, the UK, and France.
"This discovery has major implications for how we think about Earth's earliest history," said Professor Turner.
Historically, geoscientists believed that subduction zones-where tectonic plates descend beneath one another-were necessary to generate the chemical markers found in continents. However, Turner's team has shown that these signatures were present in Earth's primordial crust, or protocrust, long before tectonic processes began.
For years, the scientific community has attempted to pinpoint when plate tectonics first took hold, believing that rocks deficient in the element niobium would offer clues. These rocks are typically formed in subduction environments. Yet, repeated studies yielded contradictory dates and results.
"I began to wonder if we were asking the right question," said Turner.
To address this, researchers built detailed mathematical simulations of the Hadean Earth, a period when the planet's molten surface began to solidify and its core was still forming. These models revealed that under the early Earth's reducing conditions, niobium likely behaved as a siderophile element-gravitating toward metals and thus sinking into the core.
"I realised there might be a connection between early core formation, high siderophile element patterns, and the infamous negative niobium anomaly observed in continental crust," Turner noted.
The resulting crust, shaped before meteorite impacts altered Earth's surface, would have inherited the same geochemical profile found in continental rocks today-explaining the persistent chemical signature across geological time.
According to the team, this original crust was later modified through processes such as meteor bombardments, crustal peeling, and the initiation of tectonic movement, enriching it in silica and shaping the proto-continents.
The protocrust likely fractured, forming dense regions that would eventually seed continental development. As these fragments shifted, molten magma emerged between them, creating oceanic-style crust.
During the planet's turbulent early years, heavy meteor impacts disrupted and recycled the crust repeatedly. Tectonic activity, possibly sporadic and impact-triggered, became a more stable process around 3.8 billion years ago when meteor strikes subsided and orbital patterns stabilized.
Eventually, plate tectonics evolved into a continuous, self-sustaining mechanism.
"This discovery completely changes our understanding of Earth's earliest geological processes," Turner said. "It also gives us a new way to think about how continents might form on other rocky planets across the universe."
Research Report:Formation and composition of Earth's Hadean protocrust
Related Links
Macquarie University
Explore The Early Earth at TerraDaily.com
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