At top : Changes over time in the average silica (SiO2) content of the continents. The orange star represents the current value for continental crust, namely 67% of its mass, while the green star indicates the current value for oceanic crust, 50% of its mass. Continental crust has always been rich in silica compared to the more silica-poor oceanic crust. At bottom : Periods of major crustal growth (grey vertical bars) as recorded in sedimentary rocks over the past 3.7 billion years.
At top : Changes over time in the average silica (SiO2) content of the continents. The orange star represents the current value for continental crust, namely 67% of its mass, while the green star indicates the current value for oceanic crust, 50% of its mass. Continental crust has always been rich in silica compared to the more silica-poor oceanic crust. At bottom : Periods of major crustal growth (grey vertical bars) as recorded in sedimentary rocks over the past 3.7 billion years. Marion Garçon - One of Earth's unique features is that it has continents. Contrary to many theories, the continents have always been rich in silica (which is found in quartz for example). The continents did not form continuously over time but result from episodic events throughout Earth's history.
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