Once Upon A Green Venus

All planets' ecosystems change over time, a fact that may be unsettling to students of the greenhouse effect on Earth who cast their eyes upon Venus, where catastrophic global warming has raised surface temperatures to a toasty 850°F (464°C). Some contemporary theories argue that Venus may have once experienced a climate much more like that of today's Earth, "complete with giant rivers, deep oceans and teeming with life" (Leake, 2002, 11). Two British scientists believe that they have found some evidence that rivers the size of the Amazon once flowed for thousands of miles across the Venusian landscape, emptying into liquid water seas. According to a report by Jonathan Leake in the London Sunday Times, these scientists used radar images from a NASA probe to

Surface of Venus (Jeff Dixon)

trace the river systems, deltas, and other features they say could have been created only by moving water (Leake, 2002, 11).

Because of its thick cloud cover and searing surface temperatures, no one on Earth knew much about Venusian topography until 1990, when NASA's Magellan probe used radar to penetrate the clouds and map the surface of Venus. Magellan's images showed that the surface had been carved by large river-like channels that scientists at the time thought were caused by volcanic lava flows. Jones and colleagues reanalyzed the same images using latest computer technology and found they were too long to have been created by lava (Leake, 2002, 11).

Adrian Jones, a planetary scientist at the University College London, who carried out the research, said the findings suggested life on Venus could have evolved roughly parallel with Earth's. "If the climate and temperature were right for water to flow, then they would have been right for life, too. It suggests life could once have existed there" (Leake, 2002, 11). Studies compiled by David Grinspoon of the Southwest Research Institute at Boulder, Colorado, suggest that Venus may have been habitable for as long as 2 billion years, before an accelerated greenhouse effect dried its oceans.

Roughly 20 space exploration missions to Venus have returned enough data to construct an image of Venus today as a hellishly hot place: "[I]ts skies dominated by clouds of sulfuric acid, poisoned further by hundreds of huge volcanoes that belch lava and gases into an atmosphere lashed by constant hurricane winds" (Leake, 2002,11). Venus differs from Earth in one important respect: it has no tectonic plates that permit stresses to express themselves a little at a time, via earthquakes and volcanic eruptions. The scientists' research suggests that as recently as 500,000 years ago something (perhaps a surge of volcanic eruptions, long contained by the lack of tectonics) triggered runaway global warming that destroyed the Venusian climate and eventually boiled away the oceans (Leake, 2002, 11). According to this research, warming on Venus may have been accelerated by heat released into its atmosphere by billions of tons of carbon dioxide from rocks and, possibly, vegetation. Today, Venus' atmosphere is mainly carbon dioxide.

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