Plate tectonics started at least 3.5 billion years ago
![Yosemite National Park’s Half Dome](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2017/09/092117_CG_plate-tectonics_main.jpg?fit=860%2C460&ssl=1)
ROCK OF AGES Plate tectonics may have started as early as 3.5 billion years ago on Earth. That recycling of Earth’s surface leads to the separation of light-colored continental crust (exposed here at Yosemite National Park’s Half Dome) from darker, denser oceanic crust.
© Basil Greber