Today, the Canadian oil sands, also called tar sands, are recognized as one of the largest reservoirs of petroleum in the world.

But extracting the resource from this unique geological formation is costly-both economically, and environmentally.  It takes a great deal of labor, energy, and water to squeeze the thick, sticky bitumen from the ancient mix of sand, clay and water.

Only the surging oil prices of the past decade have made the oil sands business feasible.

Controversy now abounds over efforts to build gateways for bringing more of this oil to market, especially over TransCanada's proposed Keystone XL pipeline to the refining centers of Texas.

Now, for the first time, it is possible to step back through history and see the expansion of the oil sands business, thanks to the Landsat Earth-observing satellites managed by NASA and the U.S. Geological Survey.

The first of a series of images released last week by NASA's Goddard Space Flight Center shows the area around the Athabasca River long before the great oil sands boom was under way.

Even then, a large storage pond of toxic mine tailings was already visible. Beneath them, the first mine lay closest to the river, with the second active mine just to its left.

See the satellite photo series at the link.