Astropaleobiology in the 21st Century

Malcolm Walter and Sherry Cady

Introduction

A new discipline of paleobiology is emerging and in the 21st century may well assume profound significance. We can call it astropaleobiology. Its primary scientific objective is to locate and interpret evidence of former life on other planets or their moons. In its most successful form, astropaleobiology requires a multidisciplinary approach that includes scientific efforts from a wide range of disciplines. For example, efforts of the SETI program could be included, because if the radio telescope-based search for extraterrestrial intelligence is ever successful, then, of necessity, it will have found evidence for intelligent civilizations from the past, perhaps even from billions of years ago.

Current State

As a novel discipline, astropaleobiology is moving into high gear with the new era of Solar System exploration, which is now underway. At some time in the future astropaleobiology and its sister discipline astrobiology may come to assume roles as the disciplines that encompass life and its history in the Universe. In the US NASA is considering establishing an Astrobiology Institute and to a lesser extent there are comparable moves elsewhere. Space exploration provides us with a means to understand life's origin, evolution, and destiny in the Universe.

For our current purposes though we are focussing on the Solar System, and particularly on Mars. The reason is simply that there is good evidence that early in the history of the Solar System Earth and Mars had comparable surface environments. This is particularly true of the time from 3-4Ga.

The origins of astropaleobiology can be traced to the failure of the NASA Viking missions of the 1970's to find evidence of extant life on Mars. This, along with the rich record of planetary history the Viking and Mariner missions of the same era revealed, focussed attention on the possibility that even if there is no life there now (which is far from being established), there may well have been life there in the past. Starting in a significant way in the 1970's, planetary scientists and paleobiologists began formulating ever more precise exploration models focussed on the search for former life. This work continues and is expanding, and operates through the study of "Earth analogues" sites and deposits here that are considered comparable to target sites on Mars. Such sites include the regolith and its contained endoliths, lacustrine sediments, subterranean vadose and phreatic environments, and of special interest at present, former thermal spring deposits.

There is a particular focus on "hyperthermophiles", members of the superkingdoms Bacteria and Archaea that live at high temperatures, because molecular phylogenetic studies reveal that these lie at the base of the "Universal Tree of Life" on Earth.

This discipline rocketed into prominence last August with the announcement that a meteorite from Mars contained compelling evidence of life in Archaean times (in Earthly terms). Every aspect of the evidence is disputed but the resultant burst of activity is providing significant new information, which will improve our ability to confidently recognize evidence of past microbial communities.

The work on the meteorite also forces us to confront the strong possibility that microbes might travel between the planets aboard meteorites, and therefore that in a sense our ecosystem might extend to our planetary neighbors. Some paleobiologists in this field are now starting to consider how to recognize whether or not any life that might be found on Mars or other planets or moons had an independent origin. This is no longer science fiction.

Future

The success of this field will depend on the integration of evidence from multiple sources such as micropaleontology, organic geochemistry and isotope geochemistry. Its practitioners will require a good understanding of field geology and petrology. The biggest problem is demonstrating biogenicity, and much more effort will have to be directed to improving the necessary skills.

Astropaleobiology will confront the question "Are we alone?". A convincing demonstration of former microbial life on Mars will lead to the following questions:

1. Did it have an origin independent of life on Earth? If the answer is yes, that will be every bit as significant as a successful SETI search.
   
2. Is life on Earth the result of the inevitable consequence of physical and chemical laws - that is, the operation of the constraining effects of self-organization? Or did life travel between the planets?

The answers to these questions will have profound consequences beyond paleobiology. The search for answers will be the greatest challenge facing paleobiology in the 21st century.

Astropaleobiology Delegates

Dr. S. L. Cady--Topic Coordinator
SETI/NASA Ames Research Center
Exobiology Branch
Mail Stop N239-4
Moffett Field, CA 94035-1000 USA
scady@mail.arc.nasa.gov
650-604-3826 (PHONE)
650-604-1088 (FAX)

Dr. Malcolm Walter--Topic Coordinator
School of Earth Sciences
North Ryde, South Wales 2109, AUSTRALIA
Malcolm.walter@mq.edu.au
29-850-8354 (PHONE)
29-850-8428 (FAX)

This page is maintained for the Paleo21 Organizing Committee by Norman MacLeod and H. Richard Lane. Corrections, inquiries about, and updates to any of the information shown above should be directed to Norm and/or Rich.