How Do Continents Grow?

Continents grow like onions, with rings of younger rocks added layer by layer to the perimeter of an ancient landmass. But even though scientists know where continents get bigger, plate tectonic models have never fully explained the how.

Plate tectonics describes how the Earth's surface is divided into many tectonic plates, which are pushed and pulled about the thin crust on the surface by currents inside the mantle, the hotter, rocky layer under the crust.

One of the most enduring plate tectonic puzzles is how continental margins gobble up huge pieces of new crust without choking. Continents grow when new crust attaches at subduction zones, locations where a tectonic plate subducts, or sinks back into the mantle. Often, this new crust arrives as small fragments, called micro-continents, or volcanic island chains. (Imagine these fragments as bumps on a surfboard, but in this case, the bumps are catching a ride on top of flat oceanic tectonic plates, the surfboard.)

http://www.huffingtonpost.com/2014/03/24/plate-tectonics-continents_n_5018963.html?utm_hp_ref=science