The thinning is related to the cooling of Earth’s interior prompted by the splitting of the supercontinent Pangaea, which broke up into the continents that we have today, said Harm Van Avendonk, the lead author of the study and a senior research scientist at The University of Texas Institute for Geophysics. The findings, published in Nature Geosciences on Dec. 12, shed light on how mantle plumes and plate tectonics has influenced the cooling of the Earth’s mantle throughout geologic history.
The mantle is the very hot, but mostly solid, layer of rock between the Earth’s crust and core. Magma from the mantle forms oceanic crust when it rises from the mantle to the surface at spreading centers and cools into the rock that forms the very bottom of the seafloor. The Earth’s mantle has been cooling almost from its creation.
“It’s important to note the Earth seems to be cooling a lot faster now than it has been over its lifetime,” Van Avendonk said. “The current rate of mantle plumes allows Earth to cool much more efficiently than it did in the past.”
The research that led to the connection between the splitting of the supercontinent and crust thickness started when Van Avendock and Ph.D. student Jennifer Harding, a study co-author, noticed an unexpected trend when studying existing data from young and old seafloor. They analyzed 234 measurements of crustal thickness from around the world and found that, on a global scale, the oldest ocean crust examined – 170 million year old rock created in the Jurassic – is about one mile thicker than the crust that’s being produced today.
The link between crust thickness and age prompted two possible explanations – both related to the fact that hotter mantle tends to make more magma. Mantle plumes could have thickened the old crust by covering it in layers of lava at a later time. Or, the mantle was hotter in the Jurassic than it is now.
The finding that splitting up Pangea cooled the mantle is important because it gives a more nuanced view of the mantle temperature that influences tectonics on Earth.