No new mountains formed during Earth's middle age, halting life's evolution for an eon

February 11, 2021

During the Proterozoic, Earth grew no taller - the tectonic processes that form mountains stalled, leaving continents devoid of high mountains for nearly 1 billion years, according to a new study. Because mountain formation is crucial to nutrient cycling, the prolonged shift in crustal activity may have resulted in the "boring billion," an eon in which the evolution of Earth's life stalled. Over geologic timescales, even mountains are ephemeral. The massive tectonic forces that drive vast swaths of the planet skywards are countered by the interminable processes of erosion. Because the thickness of Earth's crust is in constant flux, tracking mountain formation over deep time is challenging, yet crucial to understanding the evolution of the planet's surface and the life that lives upon it. Here, Ming Tang and colleagues present a new proxy for understanding mountain formation (orogenic) processes. Using europium anomalies in zircons long eroded from ancient landforms to estimate the mean thickness of crust over Earth's history, Tang et al. discovered that the formation of mountains was paused for nearly a billion years during Earth's middle age. While continental crust was thick and active during the Archean and Phanerozoic eons, the Proterozoic witnessed little activity, resulting in a steady decline in crustal thickness as mountains slowly eroded away. The authors suggest that this orogenic quiescence could be linked to the long-lived Nuna-Rodina supercontinent, which may have altered the thermal structure of the mantle, weakening the activity of the continental crust above. With no new nutrients being delivered to the planet's surface, the changes may have also resulted in a persistent famine in the oceans and, thus, halted life's evolution for a time.
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American Association for the Advancement of Science

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