Interview: John A. Baross

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"We Are Too Earth-Centric in Our Search for Alien Life"

11 Jul, 2007 12:54 pm

The American National Research Council published last week a report entitled ?The Limits of Organic Life in Planetary Systems? suggesting that ?life is possible in forms different from those on Earth?. Interview with Prof John Baross, the chair of the committee that published this report.

What motivated this report?

Prior to chairing the committee that published the limits reports, I was co-chair of the NRC Committee on the Origin and Evolution of Life. This committee dealt with NASA Astrobiology issues. One of the issues discussed was the possibility that life on other planets and moons might not resemble Earth life and that perhaps too much of the emphasis in our search for life elsewhere is focused on Earth life even to the point of using specific molecular methods developed to detect Earth life. The committee recommended that a separate task group be formed to examine what we know and don’t know about the potential for alternative life forms. These potential alternative life forms might be similar to Earth life but use different biochemistries so that their nucleic acids and proteins might include different nucleotide bases and different amino acids respectively. We also wanted to explore the validity of the mantra of “follow the water” in the search for life elsewhere. Could life exist in other solvents besides water and what is known about Earth life’s ability and/or potential to grow in organic solvents? We also made the decision to limit the report to organic life and did not explore in great detail the possibility of silicon life or life that might be radically different from Earth life, such as plasma life etc. Thus our main motivation for the report was to broaden our search for life elsewhere to include life not resembling Earth life.

You call to look for weird extraterrestrial life. What do you mean by weird life?

Weird was used in this context to mean life forms that are different from Earth life, as we know it that might exist on other planetary bodies and may even still exist on Earth. I personally use weird life to describe life, as we don’t know it.

You also advocate to search Earth for weird life. What sort of new lives do you expect to discover on Earth and how do you intend to proceed?

This is an interesting question because it has several implications. The most radical is that there might have been separate origins of life on Earth, and somewhere, perhaps in some extreme environment, these different life forms may still exist. We would have to look at environments that have either not been explored such as the deep sub-seafloor crust or environments that are devoid of actively growing Earth life (ultra-dry deserts, extremely low pH or high temperature environments. Less radical would be the search for life that still harbors RNA genes that might greatly enlighten us about the origin of life on Earth assuming the presence of an “RNA world” preceding a “DNA world”. We also discuss in the report, life that may not use phosphate in DNA or ATP [ATP transports chemical energy within cells for metabolism] since phosphate would have been very limiting on the early Earth when life originated. We suggest that arsenic might be able to substitute for phosphorus in early life forms. There is also the possibility there are organisms on Earth that can grow under extreme conditions not found on Earth but exists on other planetary bodies including colder and hotter temperatures (provided there is liquid water or other usable solvents), lower pH’s and drier conditions.

“Nothing,” the report concludes, “would be more tragic in the American exploration of space than to encounter alien life and fail to recognize it.” Can you elaborate on that?

The key point is that if we are too Earth-centric in our search for alien life, we could miss alternate life forms. One of the big problems we have is that we cannot define life. We can list key characteristics of Earth life and elaborate on those characteristics we believe are canonical to all life. These characteristics do not constitute a definition of life since we don’t know the essence of what is living. We list the requirements for life and discuss whether or not they would be essential to all life even if different at the biochemical and molecular levels from Earth life. In decreasing order of certainty, life requires:

A thermodynamic disequilibrium;
An environment capable of maintaining covalent bonds, especially between carbon, hydrogen, and other atoms;
A liquid environment; and
A molecular system that can support Darwinian evolution

The report discussed these four requirements and points out that 1 and 2 are probably essential for life but that 3 and 4 may not necessarily be essential although we don’t know that. In fact, we argue in a separate section that Darwinian evolution may be essential for all life.

Interview by: Clementine Fullias

Prof John A. Baross is a professor in the School of Oceanography and the Center for Astrobiology and Evolution at the University of Washington.

Reference:

The report “The Limits of Organic Life in Planetary Systems” was published on July, 6 and posted on the Web site of the National Academies, www.nationalacademies.org

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