Such a sharp decrease in the crustal growth rate about 3 billion years ago indicates a dramatic change in the way the continental crust was generated and preserved. This change may in turn be linked to the onset of subduction-driven plate tectonics and discrete subduction zones as observed at the present day.
The growth rate of the Earth's continental crust was high during the first 1.5 billion years of the planet's history then decreased markedly for the next 3 billion years to the present day, according to new research from the University of Bristol, published today [16 March] in Science. This sharp decrease indicates a dramatic change in the way the continental crust was generated and preserved. The Earth is around 4.5 billion years old. At present 75 per cent of the continental crust - the crust we live on - is less than 1 billion years old, and only around 7 per cent of it is made up of rocks of Archaean age (that is older than 2.5 billion years). What is striking, and perhaps unexpected, is that there is increasing evidence that large volumes of continental crust were generated before 2.5 billion years ago. Thus the distribution of rocks of different ages in the continental crust was very different back in time, because of the repeated interactions between the crust, and the convecting mantle from which the crust was generated. As a consequence, the timing, rates and the geodynamical conditions of continental crust generation, destruction and reworking remain a topic of considerable debate.
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