DEER LAKE, Canada — Geologist Kirsten Oravec is in her element. "This is a walk on the Earth's mantle. These are wonderfully strange rocks," she says, marveling at the Tablelands in Gros Morne National Park. The Earth's mantle, normally hidden deep beneath the Earth's crust, is the middle layer of the planet. The collision of continents "almost 500 million years ago" catapulted the interior to ...