According to a study published in the journal Science, for nearly a billion years during our planet’s “middle age” (1.8 billion to 0.8 billion years ago), Earth’s mountains stopped growing while erosion wore down existing peaks to stumps. This extreme mountain-forming hiatus resulted from a persistent thinning of Earth’s continental crust.
At the convergent boundaries where Earth’s continental plates collide, mountains rise upward in a process called orogenesis. The continental crust at these boundaries is thicker on average and buoyed by magma, lifting surface rocks up to great heights. Meanwhile, erosion and gravity push back against peaks.When the tectonic and magmatic processes below the surface stop, erosion wins out, and the mountains are flattened.
Because even the greatest mountains disappear over time, studying ancient Earth’s crustal thickness can be the best way to measure how actively mountains formed in the past. To do this the study leaders analyzed the changing composition of zircon minerals that crystallized in the crust billions of years ago.
Today, tiny grains of zircon are easily found in sedimentary rocks all over the surface of the planet. The precise elemental composition of each grain can reveal the conditions in the crust where those minerals first crystalized.
“Thicker crust forms higher mountains and crustal thickness controls the pressure at which magma changes composition, which then gets recorded by anomalies in zircons crystallizing from that magma,” said Tang, an assistant professor at Peking University in Beijing, China.
Specktor, B. (2021, February 11). Earth’s mountains disappeared for a billion years, and then life stopped evolving. Live Science. https://www.livescience.com/earth-mountains-disappear-boring-billion.html