Anders: Origin of Carbonaceous Chondrites 525 



of this energy is wasted by direct reactions between the minerals. At most, 

 only a few thousand calories per gram would be required to produce biochemical 

 compounds from simpler starting materials. If some form of life arose at this 

 point, the remaining chemical energy could sustain it for many generations. 



Any such life form would be doomed from the outset, because its energy 

 supply, once exhausted, would no longer be replenished. But the total amount 

 of energy available from this source is appreciable, f'or a liquid water zone 

 comprising 5 per cent of the volume of a 100-km. body, as much as 8 X 10'^ cal. 

 could be stored in this manner. At a typical asteroidal distance of 2.8 a.u., 

 this corresponds to the total solar energy received by the body in 2 X 10^ years. 



Of course, the futility of a doomed subterranean life form based upon a finite 

 supply of energy makes it less appealing to the human mind than a photosyn- 

 thetic form with a life expectancy approaching that of the planet or its central 

 star. But if life arose by a spontaneous event, without guidance from above, 

 then the probability of this event would have depended upon the chemical and 

 physical conditions in the environment only, and not upon the perpetuity of 

 the energy supply. 



The suitability of asteroidal bodies as abodes of life would thus seem to 

 hinge mainly on three questions. First, were the times for water retention 

 (table 4) long enough for life to arise spontaneously? All we known about this 

 "induction period" for the origin of life is that it lasted less than 0.5 AE on 

 Earth (Kulp, 1961). Hence the asteroids cannot be disqualified on this count 

 alone. Second, were the necessary organic compounds present? From the 

 work of Calvin and Vaughn (1960), and Briggs (1961), it seems that this ques- 

 tion can be answered in the atfirmative, although Degens and Bajor's (1962) 

 observations on the bacterial production of some of these compounds may 

 require a reevaluation of the evidence. Third, could the initial hfe forms learn 

 to utilize the particular inorganic energy sources present (e.g., reactions of HoO 

 with olivine, Fe°, etc.)? No definite answer to this question is possible, al- 

 though it is perhaps relevant to point out the known, high adaptability of 

 modern terrestrial microorganisms.* 



Thus, one cannot conclude a priori that the asteroids were never capable of 

 supporting life. The question of whether life ever existed in meteorites may, 

 therefore, be examined on its own merits, because the size of the parent body 

 does not impose any major limitations. 



Isotope measurements. Further clues to the history of these meteorites come 

 from isotope measurements, although the interpretation of the data is not 

 always free from ambiguities. If we assume a simple, monotonic cooling 

 history for the meteorites, the K'^'VAr^'^ ages in table 5 give the time at which 

 the temperature of the meteorite fell to a low enough value to permit the 

 retention of radiogenic Ar'*" from the decay of K'"'. Judged from the heating 

 experiments of Stauffer (1961), interpreted according to the model of Goles et al. 

 (1960), this temperature probably lies near 200° K. Of course, short K-Ar 

 ages would also result if the meteorite were reheated at some later stage in its 



* If such subterranean life forms ever arose on the meteorite parent bodies, they are likeh' 

 to have arisen on Earth and on the moon as well. This would somewhat reduce the chances 

 of finding prebiotic organic matter on the moon (Sagan, 1961). Moreover, much of the 

 Earth's initial endowment of organic matter would have been transformed by biological 

 activity at a very early stage in its history. 



