Thursday, November 29, 2007

The Origin of Subduction

Subduction origin on early Earth: A hypothesis. 2007. Vicki L. Hansen Geology 35: 1059-1062.

How and when plate tectonics began has been enthusiastically debated for decades; since the advent of the plate tectonics theory in the early 1960s. Hansen’s paper presents a hypothesis for how plate tectonics might have begun on early Earth. According to this hypothesis, spatial and temporal overlap of internal mantle flow (“endogenic”, or internal process) and a large bolide impact (“exogenic”, or external) triggered two signature processes of plate tectonics: spreading, which leads to the formation of new crust, and Subduction, which leads to the recycling of crust.

The spatial and temporal intersection of the triggering endogenic and exogenic processes could have occurred variably across early Earth; thus, plate tectonic mechanisms could have begun at different places and different times.

Hansen’s hypothesis postulates that the ability of a terrestrial planet to develop plate tectonics results from a balance between the strength of its surface layer and the size of bolide impact it can survive—both of these factors can be related to planet size. Hansen’s hypothesis may allow us to predict if other planets could have evolved plate tectonics, and as such, might be Earth-like in character. The tectonic evolution of early Earth likely played key roles in concentrating Earth’s rich resources, and perhaps the formation and evolution of life.