Acasta

Geologists have their own mecca, a stretch of Acasta River deep in the Northwest Territories in Canada. You can get there only by canoeing for days up the river or by flying a float plane north from the town of Yellowknife, over an expanse of half land, half water. The water takes the form of thousands of lakes and ponds, some strung together into blobby rivers, in every shape that Ice Age glaciers could possibly carve. You ski to the landing near a spindly island in the middle of the river. The shore is covered with black spruce, reindeer moss, heather, and lichens. Chirping plovers cut the silence, and blackflies and mosquitoes drill your skin.

A wall of exposed rock trembles down to the water, and you can clamber down among the boulders. The rocks here are granite, dark gray hunks flecked with bits of feldspar that hook pretty much like any other piece of granite you may hae encountered. They are exceptional in only one way: some of them are more than 4 billion years old, which makes them the oldest known rocks on Earth. From our planet’s infancy the minerals that make them up have held together, as continents have been torn apart and fused back together.

Their age is so vast that it’s almost impossible to comprehend. Think of a year as equaling the length of your outstretched arms. To equal the age of the Acasta rocks, you’d have to hold hand in a line of people circling the Earth 200 times. But as hard as it may be to imagine, it is a picture that would have made Darwin very happy. - page 58