Terrestrial soils can be thought of as semi-living systems, neither alive nor dead but possessing many of the attributes of living organisms (Lin 2014). These dynamic, well-managed soils provide many ecosystem services to support life on Earth. These services can be grouped into 6 categories: (1) soils serve as a medium for plant growth, (2) soils recycle nutrients and organic matter, (3) soils modify the atmosphere through gas exchange, (4) soils store and purify water, (5) soils serve as habitat for soil organisms, and (6) soils serve as an engineering medium (Brady and Weil 2010).
The first four of these functions are of obvious use in supporting human life on starships and colonies. Soil organisms serve as a genetic “bank” of diversity, and may provide future explorers with the raw materials to create new medicines or bioengineered organisms for the purposes of ecopoiesis. A handful of soil contains billions of organisms representing a staggering diversity of natural histories (Sylvia 2005). As an engineering medium, mineral matter from the moon and asteroids has been proposed for use as radiation shields on ships and colonies (O’Neill 1977). If soil genesis can be initiated on this material, then ecologically engineered novel soils could help provide all of these services to future explorers, supplementing hydroponic and other highly engineered systems.
Lunar material does contain all of the plant macronutrients, including N, K, Ca, Mg, P, and S. These nutrients are stored as rocks and minerals including basalt, feldspar, olivine, troilite, and KREEP (K, rare earth elements, and P) deposits. Some organic toxins do occur naturally on small solar system bodies, including acetone, methyl isocyanate, acetamide, and propionaldehyde, which occur on the comet Churyumov-Gerasimenko (Goesmann et al. 2015). Quantities of such toxins will have to be determined, and resistant organisms will have to be used in the first steps of soil formation. Such organisms are already abundant in similarly contaminated soils on Earth.
Clay minerals are what drive much of the soil fertility on Earth, yet clays are unavailable without a hydrologic cycle to drive rock weathering and clay formation. Clay formation occurs on scales of hundreds to thousands of years. To ensure in-situ resources can be used, methods of accelerating clay formation, or substances that replace the unique functions of clay minerals, will have to be developed.
Brady, N. C., and R. R. Weil. 2010. Elements of the nature and properties of soils. 3rd edition. Pearson Prentice Hall, Upper Saddle River, N.J.
Goesmann, F., H. Rosenbauer, J. H. Bredehöft, M. Cabane, P. Ehrenfreund, T. Gautier, C. Giri, H. Krüger, L. Le Roy, A. J. MacDermott, S. McKenna-Lawlor, U. J. Meierhenrich, G. M. M. Caro, F. Raulin, R. Roll, A. Steele, H. Steininger, R. Sternberg, C. Szopa, W. Thiemann, and S. Ulamec. 2015. Organic compounds on comet 67P/Churyumov-Gerasimenko revealed by COSAC mass spectrometry. Science 349.
Lin, H. 2014. A New Worldview of Soils. Soil Science Society of America Journal 78:1831-1844.
O’Neill, G. K. 1977. The high frontier : human colonies in space. Morrow, New York.
Sylvia, D. M. 2005. Principles and applications of soil microbiology. 2nd edition. Pearson Prentice Hall, Upper Saddle River, N.J.