000928-1 10.1038/nsu000928-1 22 September 2000 earth Move any mountain PhilipBall Are too many men making the earth move, Philip Ball asks?

The north west highlands of Scotland contain some of the most awesome peaks in Britain, stretching over 100 kilometres just north of Fort William to Ullapool on the west coast. They are modest compared with the Himalayas, the Andes or the Swiss Alps -- but can you imagine the engineering effort it would take to build such a range, starting from plains as flat as Holland? Worse still -- imagine trying to raise the highlands to the same level as the Alps.

The human race has done this already, says Roger Hooke of the University of Maine in the journal Geology1. He estimates the total amount of earth and rock shifted by people is equivalent to a mountain range 4,000 metres high, 100 km long and 40 km wide.

Erosion in this Himalayan valley looks dramatic, but humans may now be shifting earth and rock faster than nature. Image © Dr Alan Geer
This makes human beings potentially the most active landscaping agent in the world. Our hypothetical mountain range pales compared with the world's real earth-moving power -- of which the Himalayas is perhaps the most dramatic example. But nature has been working on that for well over ten million years. People have only been shaping our surroundings for the past several thousand -- and only on a massive scale for the past few centuries.

Hooke considered how humans have been digging, excavating and generally altering the land since 3000 BC. Excavations before then were sometimes of surprising extent -- mineshafts over 10 metres deep are known -- but the iron tools and machinery of ancient civilizations allowed them much greater ambition. The Egyptians constructed a canal linking the Mediterranean to the Red Sea, for example, and the Romans paved nearly 300,000 km of roads.

But only in the Industrial Revolution did the earth really begin to move. One of the major motivations for shifting soil was to find fuel: three million tons of coal was mined in England in 1700, rising to 17 million tons by 1825. High explosives, like Alfred Nobel's gelignite in 1875, made it much easier to remove large quantities of rock in the late nineteenth century.

As Hooke points out, agriculture is one of the largest contributions to human earth movement. When trees and shrubs are removed to expose soil for cultivation, ground erodes more easily and irrigation makes this worse. And though farming practices are improving, more mouths to feed means more agriculture and greater overall damage.

The overall trend, then, is sobering. As late as 1700 the amount of earth moved globally was barely a billion tons per year; it is now about 37 billion tons per year and most of that increase came in the twentieth century.

"One may well ask how long such rates of increase can be sustained, and whether it will be rational behaviour or catastrophe that brings them to an end," Hooke says.

Hooke, R. LeB. On the history of humans as geomorphic agents. Geology 28, 843846 2000.