When we dig to obtain a precious metal, a fuel, or an ancient mine, we remove a chapter of another time. Such materials take millions of years to settle, then only moments to remove with machine and explosive.
Ever since humans first realized that the ground beneath them held hidden riches, we have dug down to discover what lies beneath. Mining makes almost every aspect of our modern lives possible, and often the effects on the natural world are far, far away from home. Unlike many of the changes humanity has brought on the planet's surface, which will disappear in time, some of our underground doings have left permanent horrible scars (伤疤)．
"The underground world for most of us is out of sight, out of mind," observes geologist Jan Zalasiewicz in England. "Yet it is seeing significant change that in some ways is as striking as any that humans have made to the Earth's geology, and that is permanent." At present, while certain tree roots can reach as much as 68 meters deep somewhere in South Africa, miners in that country have dug five kilometers below Earth's surface in pursuit of gold. The world's deepest borehole (钻孔) plunges (陡降) more than 12 kilometers into the ground.
"Things like mines and boreholes, even pressed by pressure and chemically changed by underground liquids, are big and obvious holes in the rock. They're not subtle," Zalasiewicz says. Zalasiewicz and his co-authors propose a new term for such underground disturbances: "anthroturbation". The name originates from the word "bioturbation", which refers to the kind of trace left behind in the Earth by animals such as ants when they dig their homes. Humans take this kind of disturbance to a much deeper level.
"The only way these marks can go away is by coming to the surface and being destroyed, or getting caught up in a continental crash, or some other activities," Zalasiewicz told me. "Any of these ways for erasing them will take tens to hundreds of millions of years."
