Onset of Plate Tectonics

Science  22 Jul 2011:
Vol. 333, Issue 6041, pp. 413-414
DOI: 10.1126/science.1208766

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The further back we look into the geological past, the more obscured the view, masked by an increasingly fragmentary geological record. This has resulted in a controversy on the rates and mechanisms of early continental crust formation and whether plate tectonics—the dominant crust-forming process over at least the past 2.5 billion years—operated the same way, or even at all, during early Earth history (1, 2). On page 434 of this issue, Shirey and Richardson (3) shed light on this issue by looking at it from a new angle—from the bottom up. They investigated the composition of a suite of minerals occurring as inclusions in diamonds dredged up by young kimberlite volcanoes. These diamonds derive from great depths (125 to 175 km) within the ancient lithospheric mantle keels that underpin the stable continental crustal regions known as cratons. Because the minerals can be precisely dated, they can provide a snapshot of the subcontinental lithospheric mantle (SCLM) composition at the time when the crust was being formed.