Earth’s unique continents

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Most of the crust on Earth and other rocky planets are basaltic, but Earth differs from other planets in that it has extensive regions of felsic crust, manifested in the form of continents.

The continents are billions of years old, and yet, they are restless. In their history, the continents kept changing their shapes, moved around, sometimes collided into each other, and sometimes broke apart into smaller pieces. The continents preserve the memory of our planet.

Modern study of Earth’s continents dates back to the 19^th century when F.W. Clarke first estimated the composition of the continental crust. Since then, our knowledge of Earth’s continents has grown enormously. Study of the continents has been, in part, driven by economic interests because the continental crust provides us with most of the mineral resources and energy that fuel the advance of modern civilization. From a scientific point of view, all land species, including us, owe their existence to Earth’s continents.

The more we study the continents, the more amazed we become by their profound influence on the evolution of the Earth’s habitability. Oxygen would have never accumulated in the atmosphere had the felsic continental crust not emerged. Without oxygen, large animals would have never existed on Earth. And the marine biota would have been largely muted without the nutrient continental “dirt” being continuously delivered to the ocean. Mountains rise and fall on the continents, modulating greenhouse gas CO₂ level in the atmosphere and the temperature at surface. These intrinsic relationships between Earth’s continents and surface environment point to the key role played by the continents in shaping our habitable planet.

From left to right: Mercury, Venus, Earth and Mars. Images are from web.

The continental crust is characterized by voluminous granite-type rocks, which makes it felsic (rich in Si and Al) in bulk composition. This is in contrast with the oceanic crust which forms the ocean floor and has a mafic composition (rich in Mg and Fe). Space missions in the last several decades showed that the felsic continental crust is unique to Earth. Mercury, Venus and Mars are all covered by a one-plate crust with a mafic bulk composition, much like that of Earth’s oceanic crust. Why are we so special? Why would Earth have continents? The origin of Earth’s unique continents is one of the central problems in Earth science.

I study Earth mostly through chemistry. I am particularly interested in the continental crust, its formation, evolution, and its influence on both Earth’s interior or surface environment. In this blog, I talk about my projects, including the science, thoughts, and the research stories behind.

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