New research overturns previous scientific beliefs that Earth’s tectonic plates were developed over the course of billions of years.
An artistic conception of the early Earth. Image credit: Simone Marchi / NASA.
“Plate tectonics set up the conditions for life,” said study co-author Dr. Nick Dygert, a researcher at the University of Texas at Austin.
“The more we know about ancient plate tectonics, the better we can understand how Earth got to be the way it is now.”
For the study, Dr. Dygert and his colleagues from the United States and the United Kingdom looked into the distribution of two very specific isotopes of noble gases: helium-3 (3He) and neon-22 (22Ne).
Previous models have explained the Earth’s current 3He/22Ne ratio by arguing that a series of large-scale impacts — like the one that produced our Moon — resulted in massive magma oceans, which degassed and incrementally increased the ratio of the Earth each time.
“We believe this scenario is unlikely,” Dr. Dygert said.
“While there is no conclusive evidence that this didn’t happen, it could have only raised the Earth’s 3He/22Ne ratio under very specific conditions.”
Instead, the researchers believe the 3He/22Ne ratio raised in a different way.
As the Earth’s crust is continuously formed, the ratio of helium to neon in the mantle beneath the crust increases.
By calculating this ratio in the mantle beneath the crust, and considering how this process would affect the bulk Earth over long periods of time, a rough timeline of Earth’s tectonic plate cycling can be established.
“3He and 22Ne were produced during the formation of the Solar System and not by other means,” Dr. Dygert said.
“As such, they provide valuable insight into Earth’s earliest conditions and subsequent geologic activity.”
The findings appear in the journal Earth and Planetary Science Letters.
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Nick Dygert et al. 2018. Plate tectonic cycling modulates Earth’s 3He/22Ne ratio. Earth and Planetary Science Letters 498: 309-321; doi: 10.1016/j.epsl.2018.06.044
