The Difficult Endeavor of Searching for the Signs of Life
The definition of life is going through an important redefinition. Currently even “viruses” are not generally agreed as being life : as wikipedia summarizes – Life is a characteristic that distinguishes objects that have signaling and self-sustaining processes from those that do not,[either because such functions have ceased (death), or else because they lack such functions and are classified as inanimate. We add to this “desication” in which state viruses seem “to live for ever”.
Here is a thought provoking paper on this subject : How can we best overcome our ignorance about microbial life on Earth? (AKA, “The Vast Ignorance Topic”). So it is easy, after reading this paper, to appreciate how little we know about life especially microbial life. Realization of our own knowledge limitations has been one of the reasons NASA stopped including “search for signs of life” experiments since the 1976 Viking Mission to MARS.
NASA astrobiologist Dr. Chris McKay acknowledges, for the next few years it might be all we can do to look for the “buildings” left behind by life.
It is because biologists are struggling to redefine the “markers of life” and because we worry that we might have already caused serious contamination across the solar system, that the NASA has not focused (at least since the 70’s) on experiments which “detect life”.
In 2013 though the overall mission objective changed, and it became “OK” to talk about the “search for life” or “the signs of life”.
NASA’s Chief Historian, Steven J. Dick : Why do we explore? Since the beginning of the Space Age one of the chief drivers has been the search for life beyond Earth. Already in 1962 the Space Science Board of the National Academy of Sciences declared the search for extraterrestrial life as the prime goal of NASA’s nascent space biology efforts. In doing so they realized not only the scientific but also the philosophical import of what was just beginning to be called “exobiology”: “It is not since Darwin – and before him Copernicus – that science has had the opportunity for so great an impact of man’s understanding of man.” Taking a long view, the Board found the question of life the most profound issue in the history of Western thought since modern science began with the Scientific Revolution 300 years ago”.
Winding the clock forward to 2013 : The new NASA “Vision for Space Exploration Initiative” includes an explicit directive to “search for the evidence of Life on Mars”, the NASA missions’ strategy moves from “follow the water” to “search for the signs of life”.
Recently scientists have found evidence of microbial life in 3.48 billion year old rocks in Australia, the oldest biosignatures yet found on Earth. These findings also feed into the origins of life debate, and if true, indicate that life arose relatively quickly after the late heavy bombardment of the Earth that ended about 3.8 billion years ago. These findings are likely to remain controversial over the next decade, similar to the BraiserSchopf controversy that erupted in 2002 over the 3.45 billion year old Apex chert microfossils. Such controversy is an integral part of the scientific enterprise. These are only some of the highlights of the numerous studies undertaken under the banner of astrobiology. More details are found in the Annual Reports of the NASA Astrobiology Institute (https://astrobiology.nasa.gov/nai/reports/annualreports/).
A major task will be to identify the origin of the first replicating molecules, which some researchers believe to be found in the “RNA world,” in which RNA is able to both store information and catalyze reactions.
2014 Astrobiology Strategic Plan
A good roadmap can be seen here : http://astrobiology.nasa.gov/roadmap/
The Earth Microbiome Project is a proposed, massively multidisciplinary, effort to analyze microbial communities across the globe. This project and its results will add substantially to our understanding of microbial life and will help Astrobiologists refine the 2014 Strategic Plan.