The problem of detecting life on other planets
If every living thing on Earth died tomorrow, would future generations be able to detect that animals and plants once covered the globe.?
Well, sure, if they got lucky and found the broken head of the Statue of Liberty sticking out of the sand, but two UC Berkeley researchers have so far not found distinguishing fingerprints left by the presence of life--such as erosion patterns--that could definitively determine whether or not life existed on a particular planet.
William Dietrich, professor of earth and planetary science at the University of California, Berkeley, and grad student J. Taylor Perron examined different geological features on the earth where grasses and animals change the landscape and then compared these to abiotic (i.e. without life) environments such as Chile's Atacama Desert and Mars.
The two suspected that there might be a statistically measurable difference in the number of rounded hills in areas where life thrives. Gophers, insects, tree roots and other life forms cause erosion, which wears down hills. In the Atacama, however, rounded hills are produced by salt weathering from the nearby ocean. Freeze-thaw cycles, however, can accomplish the same task and rounded hills show up in photographs from Mars.
They also looked at river meanders, which on Earth are influenced by streamside vegetation. But Mars shows meanders, too. The steepness of river courses might be a signature, too, they thought: Coarser, less weathered sediment would erode into the streams, causing the ridges to become higher. But this also is seen in Earth's mountains.
"Despite the profound influence of biota on erosion processes and landscape evolution, surprisingly, there are no landforms that can exist only in the presence of life and, thus, an abiotic Earth probably would present no unfamiliar landscapes," said Dietrich in a prepared statement.
Research, though, will continue. Right now, Mars is the only planet that we have photos of at the resolution required by this research.