Earth’s “boring billion” set the stage for complex life

"Our approach shows how plate tectonics has helped shape the habitability of the Earth," said lead author Professor Dietmar Müller. "It provides a new way to think about how tectonics, climate and life co-evolved through deep time."

Published in Earth and Planetary Science Letters, the study overturns the traditional view of the "Boring Billion," a supposedly uneventful period of Earth's history marked by little biological or geological activity. The findings reveal that the planet's tectonic plates were far from still, driving changes that produced oxygen-rich seas and the emergence of early eukaryotes -- organisms that would eventually give rise to plants, animals, and fungi.

How Nuna's Breakup Changed Earth's Climate and Seas

Eukaryotes are living things with cells that contain a nucleus and other specialized structures called organelles. Professor Müller and his team discovered that the disintegration of the supercontinent Nuna triggered a sequence of geological events that reduced volcanic carbon dioxide (CO2) emissions and expanded the shallow marine habitats where early eukaryotes evolved.

"Deep Earth processes, specifically the breakup of the ancient supercontinent Nuna, set off a chain of events that reduced volcanic carbon dioxide (CO2) emissions and expanded the shallow marine habitats where early eukaryotes evolved," Professor Müller explained.

A Dynamic Planet Beneath a 'Boring' Surface

Between 1.8 and 0.8 billion years ago, Earth's landmasses repeatedly came together and broke apart, first forming Nuna and later Rodinia. To explore this long interval, the research team developed a new plate tectonic model spanning 1.8 billion years of Earth's evolution. This allowed them to track how shifting plate boundaries and continental margins affected the exchange of carbon between the mantle, oceans, and atmosphere.

When Nuna began breaking apart about 1.46 billion years ago, the total length of shallow continental shelves more than doubled to roughly 130,000 kilometres. These expanded shallow-water zones likely supported widespread, oxygen-rich, and temperate seas -- ideal environments for early complex organisms to thrive.

At the same time, volcanic emissions of CO2 decreased, while more carbon was stored in the ocean crust as seawater interacted with hot rock along spreading ridges. This process removed CO2 from the water and trapped it in limestone deposits, locking away carbon that might otherwise have warmed the planet.

"This dual effect -- reduced volcanic carbon release and enhanced geological carbon storage -- cooled Earth's climate and altered ocean chemistry, creating conditions suitable for the evolution of more complex life," said co-author Associate Professor Adriana Dutkiewicz from the University of Sydney's School of Geosciences.

Expanding Seas and the Rise of Complex Life

The researchers found that the first fossil evidence of eukaryotes, dating to about 1.05 billion years ago, appeared during a time when continents were dispersing and shallow seas were spreading.

"We think these vast continental shelves and shallow seas were crucial ecological incubators," said Associate Professor Juraj Farkaš from the University of Adelaide. "They provided tectonically and geochemically stable marine environments with presumably elevated levels of nutrients and oxygen, which in turn were critical for more complex lifeforms to evolve and diversify on our planet."

These findings highlight a direct connection between deep-Earth processes and surface evolution, showing how plate tectonics, the carbon cycle, and biological development were intertwined over deep time.

Building a New Model of Earth's Evolution

This study marks the first time that plate tectonic reconstructions from deep geological time have been quantitatively linked to both long-term carbon cycling and key milestones in biological evolution. The team combined detailed tectonic reconstructions with computational and thermodynamic models simulating how carbon was stored and released through subduction (where one plate slides beneath another) and volcanic activity that brought magma, ash, and gases to the surface.

Together, these results offer a comprehensive framework connecting the motion of Earth's plates to the conditions that made the planet habitable -- revealing that even in its so-called "boring" billion years, Earth was quietly preparing for life's greatest transformation.