Review author

While pondering how erosion shapes landscapes, William Dietrich and his graduate student Taylor Perron realized that many models used by Earth scientists to explain the phenomenon are missing something: life. The models tend to be mechanistic and don't take into account biological factors. This led Dietrich, a professor of Earth and planetary science at the University of California, Berkeley, to wonder what Earth would have looked like if all life were removed. His subsequent search for the ‘topographic signatures’ of life generated results that have implications not only for Earth's landforms but also for whether Mars or Titan show signs of past life (see page 411). Nature caught up with Dietrich to find out more.

What was the premise that kicked this review off?

Are mountains higher or lower because of the presence of life? If so, how so, and what's the signature of that?

What was the mental exercise that started you thinking beyond purely physical erosion?

If you could examine the high-resolution topography of Earth, could you tell there was life here? I assumed we would find some distinct features reflecting biotic influences.

What did you conclude?

One of the strongest effects we found is that height, width and symmetry of mountains is influenced by life. ‘Influenced’ is the key word here — despite the pervasiveness of life on Earth, there seems not to be a unique topographic signature for it.

Couldn't the absence of a unique signature be a scaling issue?

Yes, that may be where the signature is, at the finer scale. But at the coarser scale, we can't make any conclusions.

How did the recent Mars rover images influence your work?

They rattled my cage. These images got us thinking: can we use Mars as a way to see the absence of life? But it was a shock to me as an Earthbound scientist to see how familiar Mars is. There are hill slopes on Mars that are rounded and smooth, there are valley networks with apparent regular spacing. It's the shock of the familiar.

Where do we go from here?

We'd better get our act together and bring biotic effects into geomorphic processes. Geobiology is often thought of as being microbiology. But I think this can be applied as macrobiology — how do we bring life into our purely physical equations for landscape evolution?