An interesting discovery from the Mars missions has healthy implications for virtual planets, as well as the physical ilk. The discovery is that geological formations and sweeping landscape features such as hills, valleys, mountains and plains look identical on both worlds, once you factor out the red shift in the air. That is key as for billions of years, complex life forms have existed on Earth, while Mars is as far as we have ever been able to discern, a barren, lifeless rock. The work that yielded this, was a paper published in the Jan. 26 2008 issue of the journal Nature.

Authors William E. Dietrich, professor of earth and planetary science at the University of California, Berkeley, and graduate student J. Taylor Perron reported, to their surprise, no distinct signature of life in the landforms of Earth.

"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. Instead, Dietrich and Perron propose that life - everything from the lowest plants to large grazing animals - creates a subtle effect on the land not obvious to the casual eye: more of the "beautiful, rounded hills" typical of Earth's vegetated areas, and fewer sharp, rocky ridges. "Rounded hills are the purest expression of life's influence on geomorphology," Dietrich said. "If we could walk across an Earth on which life has been eliminated, we would still see rounded hills, steep bedrock mountains, meandering rivers, etc., but their relative frequency would be different.

The similarity is disturbing for those who perhaps feel that life has left an indelible mark on the fundamental landscape of Earth - it has not. On the flip side that means that when you are laying out the base layout of your world, with the exception of a few specific features - discussed in other articles - you can ignore the length of time the planet has been inhabited, and the effects of life. These can be added after the initial ground is laid.

The problem is, that all landscape is shaped by erosion. On a small scale, and short time frame, this can be seen to be affected by plants and burrowing animals. However, the two forces - binding roots and burrowing animals - effectively cancel one another out on a large scale. With a few exceptions such as the formation of regular hills from a single original mound, life effectively removes itself from the equation.

Because the shape of the land in many locations is a balance between river erosion, which tends to cut steeply into a slope's bedrock, and the biotically-driven spreading of soil downslope, which tends to round off the sharp edges, Dietrich and Perron thought that rounded hills would be a signature of life. This proved to be untrue, however, as their colleague Ron Amundson and graduate student Justine Owen, both of the campus's Department of Environmental Science, Policy and Management, discovered in the lifeless Atacama Desert in Chile, where rounded hills covered with soil are produced by salt weathering from the nearby ocean.

"There are other things on Mars, such as freeze-thaw activity, that can break rock" to create the rounded hills seen in photos taken by NASA's rovers, Perron said.

The effect is, when you are designing your world, it will be equally realistic whether you plan for a teaming paradise planet, or a barren, atmosphere sheathed wasteland, if you design it the same way. Assume no life, and layer it on later, if necessary.

References

Life leaves subtle signature in the lay of the land