Landmasses formed 700 million years earlier than previously thought, world-first study finds

The first continental landmasses were critical for the proliferation of early life.

An international study led by Monash University geologists has found that the Earth’s earliest continents began rising above the ocean around 3.2 billion years ago - at least 700 million years earlier than most previous estimates.

Understanding when and how the first continental landmasses formed are among the most actively researched and hotly debated topics in Earth Sciences.

The study, led by Dr Priyadarshi Chowdhury, a Research Fellow from the Monash School of Earth, Atmosphere and Environment, is published today in Proceedings of the National Academy of Sciences (PNAS).

“Our study pushes back the timing and proposes a fundamentally different mechanism for the earliest continental emersion,” said Dr Chowdhury.

“We have sporadic evidence of land forming early in the history of Earth, but this is the first time we found evidence for a whole continent to have risen above sea level so early.

“The first continental landmasses were critical for the proliferation of early life.”

They created shallow marine habitats essential for photosynthetic communities and provided a steady supply of bio-essential nutrients through continental weathering and erosion.

Weathering of continental landmasses also induced dramatic changes in the Earth’s early atmosphere, oceans, and climate.

The Archean Eon witnessed fundamental changes in the composition, architecture, and rheology of the continental crust, which in turn profoundly influenced the composition of Earth’s atmosphere and oceans.

“These changes were critical to the development of some of the world’s most important metallic ore deposits,” said study co-author Dr Jack Mulder, also from the School of Earth, Atmosphere and Environment.

“For example, Earth’s largest iron ore deposits formed in the shallow seas surrounding newly emergent continental crust.”

The research team studied sedimentary rocks exposed in an ancient piece of continental crust exposed in the Singhbhum Craton of India.

They demonstrated that these sedimentary rocks were deposited in a series of rivers and coastal environments approximately 3.2 billion years ago as the Singhbhum Craton began emerging above the ocean.

Similar sedimentary rocks of comparable age are also known to be present on other ancient continental fragments, like in the Kaapvaal Craton of South Africa.

On the modern Earth, the formation of high standing continental topography is mainly driven by the subduction and collision of tectonic plates.

However, the researchers showed the emersion of continents 3.2 billion years ago was unlikely to be related to the convergence of tectonic plates.

They modelled the magmatic history of the Singhbhum Craton and suggested that emersion was driven by the emplacement of voluminous granite bodies over a 200–300-million-year period that inflated a buoyant plateau of silica-rich crust, which rose above the surrounding ocean.

“These findings challenge the prevailing view linking subaerial landmasses on the early Earth to plate tectonics,” said study co-author Professor Peter Cawood from the School of Earth, Atmosphere and Environment.

“Our research contributes to a better understanding of timescales and processes by which the Archean continental crust formed and interacted with the wider Earth system,” he said.

“This is important for developing the next generation of models for understanding the formation and location of metallic ore deposits.”

Dr Mulder said the research highlighted the interconnectedness of the Earth system through deep time by demonstrating that the formation and emersion of early continents (i.e., solid Earth and deep Earth processes) billions of years ago imparted important changes in surficial and atmospheric processes that were essential to establishing the habitable environment of the modern Earth.

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