'Despite warnings that there aren’t enough engines in a helicopter, we took a flight across the Grand Canyon. We asked if it could loop-the-loop, and the pilot said it could, but only once, so we didn’t try it. Some rocks exposed in the canyon are 1.84 billion years old—amongst the oldest exposed anywhere in the world! And although we love all rocks equally, we can’t help but have a special liking for really old ones.' (Comments by Dan, photo by Bev 19-Apr-07)