The oldest parts of Earth's continents are called cratons, and underneath, they are rooted to the mantle of the planet. Scientists have now discovered that the roots below the North American continent seem to be dripping rock blobs. The findings have been reported in Nature Geoscience.
"We made the observation that there could be something beneath the craton," said first study author Junlin Hua, PhD, who conducted the work as part of postdoctoral research at The University of Texas at Austin. "Luckily, we also got the new idea about what drives this thinning."
The study determined that the remains of a tectonic plate that is sinking into Earth's mantle may be causing this thinning in the craton, which covers the majority of the US and Canada..
Cratons are usually known to be extremely stable; they can hold up for billions of years. But there also seem to be changes that may occur in cratons, which could involve the removal of many layers of rock, and may disrupt their stability. The deepest root layer of the North China craton is thought to have been lost millions of years ago, for example.
This study may reveal the first evidence of "cratonic thinning" in action. Now scientists can take observations of the process as it happens.
But there is no need for concern. Though the dripping seems to be most pronounced over the United States Midwest, the continent won't fall apart and the landscape won't change.
The processes in the mantle that lead to this dripping may also influence tectonic plates, but these changes happen very slowly. Eventually, the dripping is expected to stop when the tectonic plate's remnants sink deep enough to stop affecting the craton.
"This sort of thing is important if we want to understand how a planet has evolved over a long time," explained study co-author Thorsten Becker, a professor at the University of Texas. This work helps scientists understand how continents form, how they may break, and how it's all returned to the Earth or recycled.