The Last Word On Nothing

Heat rises, cold falls, and like a pan of soup on a hot stove, the earth boils, exceedingly slowly.  The boiling is called convection:  columns of heat rise from the earth’s hot core, move up through the viscous solidity of the mantle, cool at the crust, roll over and fall back down.  The crust that rolls along the top of the mantle is broken into continental plates which move with the boil, pushing up and apart where heat is rising, sinking under and down where the cold falls.  And thus the continents are recycled.  It’s all just physics.  But certain parts of the continents called cratons – places in, for instance, Canada, South Africa, Australia  — don’t recycle.  They just sit there while their plates move around them, they’re a couple hundred kilometers deep, they’re like stable keels, and how they manage the stability has been a mystery.

The answer turns out to be not terrifically sexy.  The roots of the cratons, the bottom of the keels, are lined with minerals that are unusually dry, and the more viscous mantle just flows around them.  This research was published in a recent Nature magazine and the editors liked it in spite of its unsexiness.  They said that the work was difficult, measuring the water content of tiny grains of minerals, pulling samples up from the continent’s roots; and doing both while making “a compelling scientific case marks a triumph for those involved,” wrote the editors.  “The work may not make headlines, but it deserves recognition.”

So here it is.  Let’s recognize it.

Photo credits:

Boiling (gold paint on convecting acetone):   WikiRigaou

Rolling with the Boil (Digital Tectonic Activity Map) (click on it, it’s gorgeous):  NASA