New research published recently in the journal Science Advances considers the process of tectonic plate subduction. The study is a collaboration between scientists at the Scripps Institution of Oceanography at UC San Diego and the University of Chicago. It suggests that plate subduction could have initiated approximately 3.75 billion years ago.
Understanding the timeline of plate subduction will help to illuminate how life came to be on Earth. Lead author Sarah Aarons, a geochemist and assistant professor at Scripps, explains that one of the clues to configuring this puzzle is a collection of rocks from the Acasta Gneiss Complex in the Canadian tundra. The gneisses in this region date back 4.02 billion years from the Hadean eon. Aarons was particularly interested in looking at the titanium present in the ancient rocks.
"A lot of previous work has been done on these rocks to carefully date them, and provide the geochemical and petrological context," said Aarons. "We were very lucky to get the opportunity to measure titanium isotope compositions, a burgeoning isotope system in these samples."
By comparing the titanium isotopes in the old-gneiss samples with samples from modern rocks formed in subduction zones, she noted similarities in structure and composition. This finding points towards the initiation of the process of plate subduction around 3.75 billion years ago.
"While the trend in the titanium isotope data does not provide evidence that plate tectonics was happening globally, it does indicate the presence of wet magmatism, which supports subduction at this time," explains Aarons.
Previous studies have suggested many time periods when plate subduction could have begun – estimates range from 0.85 to 4.2 billion years ago – leaving the question still mostly unanswered. If scientists were able to answer this question once and for all, we would be able to say when Earth transitioned from transient landmasses to settled continents, later allowing for the establishment of the long-term biogeochemical cycles that are a result of volcanic degassing and recycling into Earth's interior.