There's nothing dramatic in this parkland view. Like the land, the clouds are flat, gray, and low on a vast landscape. Let this vastness be an analogy for the depth of geological time, with long intervals of slow, perhaps even unrecognizable change separated by abrupt boundaries impacting the entire globe. Let ~1950 be one of those boundaries for its global extent. Earlier boundaries for the base of significant human activity are merely regional, perhaps the 18^th century beginning of fossil-fueled industry, the 15^th century age of exploration, the most ancient civilizations ten millennia ago, the first human-caused mass extinction at human hands about 40 millennia ago, or the dawn of truly human cognition several hundred thousand years ago.