Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Life leaves subtle signature in the lay of the land

27.01.2006


One of the paradoxes of recent explorations of the Martian surface is that the more we see of the planet, the more it looks like Earth, despite a very big difference: Complex life forms have existed for billions of years on Earth, while Mars never saw life bigger than a microbe, if that.


Two hillslopes in the Atacama Desert of Chile – one of bedrock (A) and the other covered with soil (B) – look amazingly like the Columbia Hills on Mars (C) once the yellowish grey Martian sky has been artificially colored blue and the red color of the rocks has been removed. (Mars image, acquired by the rover Spirit, courtesy of NASA/JPL/Cornell University)


A perspective view of the Gabilan Mesa of central California, derived from a high-resolution laser altimetry map. Such distinct, periodically spaced ridges and valleys result from erosional processes that are strongly influenced by biota. Nonetheless, no unique topographic signature of life on Earth has yet been found.



"The rounded hills, meandering stream channels, deltas and alluvial fans are all shockingly familiar," said William E. Dietrich, professor of earth and planetary science at the University of California, Berkeley. "This caused us to ask: Can we tell from topography alone, and in the absence of the obvious influence of humans, that life pervades the Earth? Does life matter?"

In a paper published in the Jan. 26 issue of the journal Nature, Dietrich 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."

When a NASA scientist acknowledged to Dietrich a few years ago that he saw nothing in the Martian landscape that didn’t have a parallel on Earth, Dietrich began thinking about what effects life does have on landforms and whether there is anything distinctive about the topography of planets with life, versus those without life.

"One of the least known things about our planet is how the atmosphere, the lithosphere and the oceans interact with life to create landforms," said Dietrich, a geomorphologist who for more than 33 years has studied the Earth’s erosional processes. "A review of recent research in Earth history leads us to suggest that life may have strongly contributed to the development of the great glacial cycles, and even influenced the evolution of plate tectonics."

One of the main effects of life on the landscape is erosion, he noted. Vegetation tends to protect hills from erosion: Landslides often occur in the first rains following a fire. But vegetation also speeds erosion by breaking up the rock into smaller pieces.

"Everywhere you look, biotic activity is causing sediment to move down hill, and most of that sediment is created by life," he said. "Tree roots, gophers and wombats all dig into the soil and raise it, tearing up the underlying bedrock and turning it into rubble that tumbles downhill."

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.

They also looked at river meanders, which on Earth are influenced by streamside vegetation. But Mars shows meanders, too, and studies on Earth have shown that rivers cut into bedrock or frozen ground can create meanders identical to those created by vegetation.

The steepness of river courses might be a signature, too, they thought: Coarser, less weathered sediment would erode into the streams, causing the river to steepen and the ridges to become higher. But this also is seen in Earth’s mountains.

"It’s not hard to argue that vegetation affects the pattern of rainfall and, recently, it has been shown that rainfall patterns affect the height, width and symmetry of mountains, but this would not produce a unique landform," Dietrich said. "Without life, there would still be asymmetric mountains."

Their conclusion, that the relative frequency of rounded versus angular landforms would change depending on the presence of life, won’t be testable until elevation maps of the surfaces of other planets are available at resolutions of a few meters or less. "Some of the most salient differences between landscapes with and without life are caused by processes that operate at small scales," Perron said.

Dietrich noted that limited areas of Mars’ surface have been mapped at two-meter resolution, which is better than most maps of the Earth. He is one of the leaders of a National Science Foundation (NSF)-supported project to map in high resolution the surface of the Earth using LIDAR (LIght Detection And Ranging) technology. Dietrich co-founded the National Center of Airborne Laser Mapping (NCALM), a joint project between UC Berkeley and the University of Florida to conduct LIDAR mapping showing not only the tops of vegetation, but also the bare ground as if denuded of vegetation. The research by Dietrich and Perron was funded by NSF’s National Center for Earth-surface Dynamics, the NSF Graduate Research Fellowship Program and NASA’s Astrobiology Institute.

Robert Sanders | EurekAlert!
Further information:
http://www.berkeley.edu

More articles from Earth Sciences:

nachricht New research calculates capacity of North American forests to sequester carbon
16.07.2018 | University of California - Santa Cruz

nachricht Scientists discover Earth's youngest banded iron formation in western China
12.07.2018 | University of Alberta

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

Im Focus: Chemical reactions in the light of ultrashort X-ray pulses from free-electron lasers

Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.

Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

Microscopic trampoline may help create networks of quantum computers

17.07.2018 | Information Technology

In borophene, boundaries are no barrier

17.07.2018 | Materials Sciences

The role of Sodium for the Enhancement of Solar Cells

17.07.2018 | Power and Electrical Engineering

VideoLinks
Science & Research
Overview of more VideoLinks >>>