Knowing the fertilities of Solar System materials can help in guiding us to search for life in the Solar System, and in identifying useful soils for space colonies and planetary terraforming. The biological and nutrient tests above can be used to compare and rate the fertilities of these materials.

Many parameters contribute to soil fertility. Important factors are the amount of available nutrients and the ability of the soil to hold and gradually release the nutrients. The latter is measured by the so-called "cation exchange capacity" which measures how much ionic nutrient such as calcium, magnesium and potassium can bind and then be released from a kilogram of soil.

+++ = high rating; ++ = medium rating;

+ = low rating; 0 = zero or negative rating.

(M. Mautner, Icarus 2002, 158, 72)

Each of the above microbial, algal, plant and nutrient tests yielded the relative fertilities of the meteorites and reference materials as defined by a particular test. These results may be combined to rate the overall biological potentials of these materials. However, each type of data is measured in different units. For example, nutrients are measured as the content of the nutrient in a kilogram of soil; algae and microbial yields are measured as the number of cells produced per milliliter of meteorite extract and tissue culture yields are measured as the average weight of the plants grown in each extract.

To combine these measures, we can first rank each material relative to the others according to each test. Next, the rankings can be combined for an overall rating. For example, material A may rank number 1 amongst ten materials according to its phosphate content, number 4 according to algal yield and number 2 according to plant yield. Its average ranking would be then 2.3 out of the ten materials. A statistical test based on a similar approach in principle is called the Z score (see box below).

The overall ratings assign an overall very high (VH) fertility rating to the Martian meteorite EETA 79001 and the other Martian meteorite DaG 476 receives a high (H) rating. These results probably reflect the high content of extractable nitrate and phosphate in these materials, maybe because there may not have been water in the cooling magma on Mars to leach out the soluble nutrients when these materials formed.

The carbonaceous chondrites Allende and Murchison also received a high (H) fertility rating, similar to a lava ash that is used by NASA as a lunar simulant similar to a sample collected by the Apollo astronauts. Such lava ashes are usually fertile soils. Interestingly, all of the planetary materials that we tested received higher ratings than a productive agricultural soil from New Zealand. This suggests that the asteroid and planetary materials are at least as fertile as productive terrestrial soils.

For example, the extract of the Murchison meteorite yielded 3.1% and the DaG 476 Martian meteorite yielded 14.1% compared with algal populations in an optimized growth medium. The average yield was 8.7% of the optimized yield, with a std of 6.9%. Accordingly, the Murchison meteorite received a Z score of –0.82, and DaG 476 received a Z score of 0.78 in the algal test. The other biological and nutrient tests were evaluated similarly.

In summary, carbonaceous chondrite materials in asteroids and comets are most likely resources in the Solar System. The limiting nutrients in these resources such as nitrogen or phosphorus determine the total integrated biomass that can exist during the next five billion year main sequence phase of the Sun. On these time scales wastage is also critical. Minimizing the rate of wastage to 0.01% of the biomass per year would allow a permanent human population of several billions during this period. Further projections are speculative but biological life may survive the Red Giant phase of the Sun and may continue under the White Dwarf Sun for 10²⁰ years. Ultimately, the span of biological life may be limited by the sources of energy and by the proton decay, but these time spans may reach over 10³⁴ years.

Current cosmology requires us to re-examine our ethics. In particular, it must be considered that biological life, or even other abstract "life", has finite duration. However, the physics are uncertain, and more solid predictions may require trillions of years of observation. If life is indeed finite, a measure is needed to quantify its amount. Time-integrated biomass was used here. The calculations showed that the potential amount of life in the cosmological future is immensely greater than past life.

On the long run, Life-centered ethics is a necessary adaptation to a demanding universe, as it will propagate the species: those who chose to propagate life will be chosen by the logic of life for propagation. With these species will survive our family of organic life and possibly our human genetic heritage. It will be for our remote descendants to explore if Nature can be transformed in their favor and if Life can be extended to eternity.

2. Resources for Life in Space