Mariner 9 discovered features on Mars that seemed to be carved by running water, features that looked hauntingly similar to those on Earth studied by geologist Harlen Bretz. Beginning in the 1920s, Bretz studied a bizarre thirty-seven hundred square mile area in Washington State that he called the Channeled Scablands, a place strewn with house-sized boulders and scarred with enormous ravines, jagged cataracts, and great ridges of sand and gravel.
Bretz was determined to find out how the landscape had become so scarred. After years of study, he concluded that during the last ice age, thirteen thousand years earlier, a lake had formed along the Montana-Idaho border behind a glacial dam. He theorized that one day the dam burst; three thousand square miles of water three hundred feet high suddenly exploded across the Idaho panhandle and through Washington State into the Pacific, leaving the ragged landscape behind it.
It took decades, but Bretz finally managed to win acceptance for his theory, and shortly thereafter, planetary scientists began to compare photos taken of the Scablands by a sophisticated earth-orbiting satellite called Landsat with Mariner's images of the enormous Martian channels. Indeed, they looked so similar that some scientists began to suggest that leviathan floods had formed the strange features on Mars as they had on Earth. No one could say what had caused the Martian deluges, but based on the evidence, some theorized they were created when meteors plummeted into the planet or volcanoes suddenly erupted, transforming the Martian permafrost into surging oceans of water and mud.
The catastrophic-flood theory explained the wide, gouged channels that seem to have sprung out of nowhere, but not the more ancient, Earth-like riverbeds that Mariner 's cameras had found. These, most scientists now believe, could only have been formed by running water that existed when the planet was warmer and had a denser atmosphere. But baffling and fascinating questions still remained. If Mars once had rivers of water, could life have established a toehold there as it had on Earth? Could we find a way to recreate those past conditions that perhaps made Mars more Earth-like? Scientists would have to continue their investigations.
