A reconstruction of Earth’s continental crust over the eons shows that our planet’s land masses are eroding faster than they’re being replenished—meaning our entire planet could become completely submerged in about two billion years.
By studying the concentrations of isotopes from 13,000 rock samples taken around the world, geologist Bruno Dhuime and his team from the University of Bristol, UK, were able to estimate the thickness of Earth’s continental crust at various points in history, and then use those findings to project into the future. The results of their work can be found at Nature Geoscience, but New Scientist offers a tidy summary of the team’s findings:
Continents today are about 35 kilometres thick, on average, with the buoyant rock bobbing next to the 7-kilometre-thick, denser oceanic crust, which rides lower.
But before about 3 billion years ago, Dhuime thinks, the continents were slimmer. Having less volume made them less buoyant, meaning they couldn’t float up above sea level.
Once plate tectonics began on Earth in earnest, the continents spent the next 2 billion years beefing up when plates collided, pushing the crust up. Continental crust peaked in thickness about a billion years ago – around the time Earth’s mightiest continents banded together to form the supercontinent Rodinia.
The mountains raised by that event have been eroding ever since, and not enough new crust is forming to offset the losses.
“If it continues for the next 2 billion years, then the crust will again reach that state where the continents are submerged beneath the ocean,” Dhuime says.
As the New Scientist report points out, however, Dhuime’s analysis fails to take other factors into account, including the rate at which magma attaches to the base of the crust, and not just the build-up of crust at plate convergence points.
What’s more, a runaway greenhouse gas effect—either one that’s human-caused or natural—could eliminate much of the Earth’s water well before then. Some estimates suggest our planet will be water free in about 1.1 billion years, making concerns of a water world rather moot.
Read the entire article at New Scientist. And check out the scientific study at Nature Geoscience: “Emergence of modern continental crust about 3 billion years ago”.