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Nucleotide Synthesis under Possible Primitive Earth ConditionsAuthor(s): Cyril Ponnamperuma and Ruth MackReviewed work(s):Source: Science, New Series, Vol. 148, No. 3674 (May 28, 1965), pp. 1221-1223Published by: American Association for the Advancement of ScienceStable URL: http://www.jstor.org/stable/1716205 .

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lization from the liquid state underhigh pressure is oriented along thisplane.By this method it was possible tofollow the liquidus line of sulfur upto 60 kb (Fig. 1). The slope of the

liquidus curve shows that the slope ofthe line changes from positive to verti-cal with increasing temperature andpressure. According to the Clausius-Clapeyron expression, vertical behaviormeans that the difference in specificvolume between the solid and liquidsulfur disappears, that is to say, theirdensities are equal.The quenching experiments wereconducted in the area of the tempera-ture-pressure diagram in which thesolid sulfur is the stable phase. Thex-ray diffraction patterns showed twocrystalline forms. One form was theconventional rhombic sulfur and theother was a new cubic form, a =13.66 A (Table 1). The data plottedin Fig. 1 show that the triple point ofcubic, rhombic, and liquid sulfur isat a pressure of 28 - 4 kb and a tem-perature of 300? ? 5?C. The slope ofthe boundary line between cubic andrhombic sulfur is negative, which, ac-cording to the Clausius-Clapeyron ex-pression, occurs because the densityof cubic sulfur is higher than thatof rhombic sulfur. The density ofquenched samples of cubic sulfur wasdetermined by the sink-float methodin two experiments: the results were2.18 and 2.19 g cm-3 at 30?C, re-spectively. The normal density ofrhombic sulfur is 2.04 g cm-3. Theheat of transformation from rhombicto cubic sulfur was calculated as 49 ?5 cal g-l, based on a temperature of30?C and a pressure of 1 atm. Theheat of transformation would be dif-ferent if the density difference changedsignificantly with increase in pressure.The cubic form is light yellow and in-soluble in carbon disulfide; the unitcell contains 104 sulfur atoms.

TRYGGVE BXAKOwens-Illinois Technical Center,1700 North Westwood, Toledo, OhioReferences

1. B. Meyer, Chem. Rev. 64. 429 (1964).2. H. Rose and 0. Miigge, Neues Jahrb. Min-eral. 48, 250 (1923).3. P. W. Bridgman, Phys. Rev. 48, 825 (1935);Proc. Aner. Acad. Arts Sci. 76, 1 (1945).4. H. G. David and S. D. Hamann, J. Chemn.Phys. 28, 1006 (1958); S. D. Hamann, Aus-tralian J. Chem. 11, 391 (1958).

lization from the liquid state underhigh pressure is oriented along thisplane.By this method it was possible tofollow the liquidus line of sulfur upto 60 kb (Fig. 1). The slope of the

liquidus curve shows that the slope ofthe line changes from positive to verti-cal with increasing temperature andpressure. According to the Clausius-Clapeyron expression, vertical behaviormeans that the difference in specificvolume between the solid and liquidsulfur disappears, that is to say, theirdensities are equal.The quenching experiments wereconducted in the area of the tempera-ture-pressure diagram in which thesolid sulfur is the stable phase. Thex-ray diffraction patterns showed twocrystalline forms. One form was theconventional rhombic sulfur and theother was a new cubic form, a =13.66 A (Table 1). The data plottedin Fig. 1 show that the triple point ofcubic, rhombic, and liquid sulfur isat a pressure of 28 - 4 kb and a tem-perature of 300? ? 5?C. The slope ofthe boundary line between cubic andrhombic sulfur is negative, which, ac-cording to the Clausius-Clapeyron ex-pression, occurs because the densityof cubic sulfur is higher than thatof rhombic sulfur. The density ofquenched samples of cubic sulfur wasdetermined by the sink-float methodin two experiments: the results were2.18 and 2.19 g cm-3 at 30?C, re-spectively. The normal density ofrhombic sulfur is 2.04 g cm-3. Theheat of transformation from rhombicto cubic sulfur was calculated as 49 ?5 cal g-l, based on a temperature of30?C and a pressure of 1 atm. Theheat of transformation would be dif-ferent if the density difference changedsignificantly with increase in pressure.The cubic form is light yellow and in-soluble in carbon disulfide; the unitcell contains 104 sulfur atoms.

TRYGGVE BXAKOwens-Illinois Technical Center,1700 North Westwood, Toledo, OhioReferences

1. B. Meyer, Chem. Rev. 64. 429 (1964).2. H. Rose and 0. Miigge, Neues Jahrb. Min-eral. 48, 250 (1923).3. P. W. Bridgman, Phys. Rev. 48, 825 (1935);Proc. Aner. Acad. Arts Sci. 76, 1 (1945).4. H. G. David and S. D. Hamann, J. Chemn.Phys. 28, 1006 (1958); S. D. Hamann, Aus-tralian J. Chem. 11, 391 (1958).5. T. Berger, S. Joigneau, G. Bothet, Compt.Rend. 250, 4331 (1960).6. E. V. Zubova and L. A. Korotaeva, Zh. Fiz.Khim. 32, 1576 (1958).11 March 196528 MAY 1965

5. T. Berger, S. Joigneau, G. Bothet, Compt.Rend. 250, 4331 (1960).6. E. V. Zubova and L. A. Korotaeva, Zh. Fiz.Khim. 32, 1576 (1958).11 March 196528 MAY 1965

Nucleotide Synthesis under PossiblePrimitive Earth Conditions

Abstract. The nucleosides adenosine,guanosine, cytidine, uridine, and thy-midine were each heated with inor-ganic phosphate. Nucleoside monophos-phates were formed in appreciableyield. This result has a bearing on thehypothesis of chemical evolution.

In our study of chemical evolutionthe main endeavor has been to recon-struct the path by which the constitu-ents of the nucleic acid molecule couldhave arisen on the primordial earthbefore the appearance of life. The syn-thesis of the bases, adenine andguanine, and the sugars, ribose anddeoxyribose, under simulated primitiveearth conditions has been demonstratedearlier (1). Recent experiments havealso shown that the nucleosides, adeno-sine and deoxyadenosine, could beformed in such an environment (2).Several attempts have already beenmade to synthesize nucleotides abiotic-ally (3). Previously, we found that,when a dilute solution of adenine andribose was irradiated with ultravioletlight in the presence of ethyl meta-phosphate, the nucleotides AMP, ADP,ATP, and A4P (mono-, di-, tri-, andtetraphosphates of adenosine) wereformed. Although the source of phos-phorus used in this experiment was notone most likely to be found on theprimitive earth, the result clearly estab-lished that the process could occurabiotically. We now find that the simpleexpedient of heating a nucleoside witha source of inorganic phosphate givesrise to the nucleoside monophosphatesin appreciable yield.In a series of experiments, the nu-cleosides adenosine, guanosine, cyti-dine, uridine, and thymidine wereheated with sodium dihydrogen ortho-phosphate, NaH2PO4. Two sets of ex-periments were performed. In the first,the nucleosides were labeled with 14C(specific activity of i mc/mmole). Inthe second, the phosphate was alsolabeled with 2p. An aqueous solution,100 LI, containing 2 umole of a nu-cleoside and 2 ,umole of the phosphatewas placed in a 5-ml pyrex tube andlyophilized. By this method a film ofsolid material containing an intimatemixture of the nucleoside and the phos-

Nucleotide Synthesis under PossiblePrimitive Earth Conditions

Abstract. The nucleosides adenosine,guanosine, cytidine, uridine, and thy-midine were each heated with inor-ganic phosphate. Nucleoside monophos-phates were formed in appreciableyield. This result has a bearing on thehypothesis of chemical evolution.

In our study of chemical evolutionthe main endeavor has been to recon-struct the path by which the constitu-ents of the nucleic acid molecule couldhave arisen on the primordial earthbefore the appearance of life. The syn-thesis of the bases, adenine andguanine, and the sugars, ribose anddeoxyribose, under simulated primitiveearth conditions has been demonstratedearlier (1). Recent experiments havealso shown that the nucleosides, adeno-sine and deoxyadenosine, could beformed in such an environment (2).Several attempts have already beenmade to synthesize nucleotides abiotic-ally (3). Previously, we found that,when a dilute solution of adenine andribose was irradiated with ultravioletlight in the presence of ethyl meta-phosphate, the nucleotides AMP, ADP,ATP, and A4P (mono-, di-, tri-, andtetraphosphates of adenosine) wereformed. Although the source of phos-phorus used in this experiment was notone most likely to be found on theprimitive earth, the result clearly estab-lished that the process could occurabiotically. We now find that the simpleexpedient of heating a nucleoside witha source of inorganic phosphate givesrise to the nucleoside monophosphatesin appreciable yield.In a series of experiments, the nu-cleosides adenosine, guanosine, cyti-dine, uridine, and thymidine wereheated with sodium dihydrogen ortho-phosphate, NaH2PO4. Two sets of ex-periments were performed. In the first,the nucleosides were labeled with 14C(specific activity of i mc/mmole). Inthe second, the phosphate was alsolabeled with 2p. An aqueous solution,100 LI, containing 2 umole of a nu-cleoside and 2 ,umole of the phosphatewas placed in a 5-ml pyrex tube andlyophilized. By this method a film ofsolid material containing an intimatemixture of the nucleoside and the phos-phate was deposited on the walls of thetube. The tube was then sealed andheated to 160?C for 2 hours. After thetube was cooled to room temperature

phate was deposited on the walls of thetube. The tube was then sealed andheated to 160?C for 2 hours. After thetube was cooled to room temperature

the seal was broken, and the contentswere dissolved in 200 /l of water. Thissolution containing the reaction prod-ucts was then analyzed.The analytical techniques used wereelectrophoresis, paper chromatography,electrophoresis combined with paperchromatography, and ion-exchangechromatography. In each one of thesemethods the identification of individualproducts was made with the coincidencetechnique of chromatography (4). Thismethod, which had earlier been usedby us for paper chromatography alone,was now extended to electrophoresisand ion-exchange chromatography.The electrophoresis was performedat 1500 volts with a Pherograph (5).With a pH 3.5 buffer and Whatman3MM paper, a satisfactory separationwas effected in 1 hour (6). A 50-1/lsample containing approximately 0.51zc of the material to be analyzedwas streaked at the origin with 10 jugof each of the 2'-, 3'-, and 5'-monophosphates and cyclic 2',3'-phos-phate as nonradioactive carriers. Theradioactive spots were located as darkareas on an autoradiograph, and thenonradioactive carriers appeared on ashadowgram as bright spots on a darkbackground. There was coincidencebetween the light area on the shadow-gram and a dark area on the auto-radiograph. This indicated that materialhaving the same electrophoretic mobil-ity as the carriers at pH 3.5 had beensynthesized in the experiment. Figure 1illustrates such an analysis for fivedifferent experiments starting withadenosine, guanosine, cytidine, uridine,

the seal was broken, and the contentswere dissolved in 200 /l of water. Thissolution containing the reaction prod-ucts was then analyzed.The analytical techniques used wereelectrophoresis, paper chromatography,electrophoresis combined with paperchromatography, and ion-exchangechromatography. In each one of thesemethods the identification of individualproducts was made with the coincidencetechnique of chromatography (4). Thismethod, which had earlier been usedby us for paper chromatography alone,was now extended to electrophoresisand ion-exchange chromatography.The electrophoresis was performedat 1500 volts with a Pherograph (5).With a pH 3.5 buffer and Whatman3MM paper, a satisfactory separationwas effected in 1 hour (6). A 50-1/lsample containing approximately 0.51zc of the material to be analyzedwas streaked at the origin with 10 jugof each of the 2'-, 3'-, and 5'-monophosphates and cyclic 2',3'-phos-phate as nonradioactive carriers. Theradioactive spots were located as darkareas on an autoradiograph, and thenonradioactive carriers appeared on ashadowgram as bright spots on a darkbackground. There was coincidencebetween the light area on the shadow-gram and a dark area on the auto-radiograph. This indicated that materialhaving the same electrophoretic mobil-ity as the carriers at pH 3.5 had beensynthesized in the experiment. Figure 1illustrates such an analysis for fivedifferent experiments starting withadenosine, guanosine, cytidine, uridine,

Fig. 1. Reaction between "'C-nucleosidesand NaH2PO4;autoradiograph shows elec-trophoretic separation of products at pH3.5. The monophosphates were indentifiedby the coincidence technique. Several un-identified bands are present.1221

Fig. 1. Reaction between "'C-nucleosidesand NaH2PO4;autoradiograph shows elec-trophoretic separation of products at pH3.5. The monophosphates were indentifiedby the coincidence technique. Several un-identified bands are present.1221

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Table 1. Totaluridinemonophosphateormedwith different phosphates.Mono-Phosphate phosphateused obtained(%)

NaH,POtH,>H 16.0Na,l-PO,-7HE0 0.6Na3PO,.12H20 0.6NaNH HPO,.4HO2 13.1NH,He,PO, 5.9(NI-1,) HPO 13.4H:PO, 8.3Ca(H,PO1)2,-H.20 10.5Ca:,(PO1),2 0.1

and thymidine. At pH 3.5, the 2'-, 3'-,and 5'-nucleotides did not separatefrom each other. When the electro-phoresis was performed at pH 8, the2'- and 3'-nucleotides moved togetherapart from the 5'-monophosphate (7).A more definite identification was ob-tained for each of the nucleosides bytwo-dimensional electrophoresis, at pH3.5 in one direction and at pH 8 in theother. Here again coincidence betweenautoradiograph and shadowgram wasused as the criterion of identity.For paper chromatography we usedthe method described (4). The mono-phosphates and cyclic phosphates fromthe electrophoretic separation wereeluted and chromatographed on What-man No. 1 paper, with isobutyric acidand 0.5N ammonium hydroxide (5:3by volume) in one direction, and withbutanol-1, propionic acid, and water(14 : 9 : 10 by volume) in the other. Atwo-dimensional chromatogram wasprepared for the reaction products ofeach of the nucleosides. Nonradioactivecarriers were present in the material

Fig. 2. Autoradiograph illustrating separa-tion of 'C-uridine monophosphates bypaper .chromatography in one directionand electrophoresis in the other.1222

eluted from the electrophoregram. Thecoincidence technique established thepresence of the 5'-, the cyclic 2',3'-and the 2'- or 3'-monophosphates. Inthe chromatographic system used the2'- and 3'-monophosphates traveled asa single spot. Hydrolysis of thecyclic 2',3'-phosphate with 0.1N HCIfor 4 hours at room temperature yieldedonly 2'- and 3'-phosphates, establishingthe nature of 2',3'-linkage (8).In a further scheme of analysis wecombined paper chromatography withelectrophoresis. Figure 2 illustrates sucha separation in the case of uridine. Theelectrophoresis at pH 3.5 was per-formed under the same conditions asbefore. Paper chromatography in thesecond dimension was effected withsaturated ammonium sulfate, isopro-pyl alcohol, 1M sodium acetate (80:2: 18 by volume) (9). By the use ofappropriate standards, the 2'-, 3'-, andthe 5'-monophosphates and the cyclic2',3'-phosphate were identified. Hereagain the 2'-monophosphate was notseparated from the 3'-nmonophosphate.As neither electrophoresis nor paperchronmatography was able to separate2'- and 3'-monophosphates from eachother, we turned to ion-exchangechromatography. A Dowex-I formnatecolumn (1 by 15 cm) was used forthis purpose (10), The separation ofthe cytidine monophosphates is shownin Fig. 3. The sample was added in 0.5ml of water; 0.02M formic acid wasused as the eluant. Known nonradio-active carriers, 5'-, 2'-, and 3'-cytidinemonophosphates, were added to thecolumn. The eluant from the columnpassed through an ultraviolet analyzerwhich continuously recorded the ultra-violet absorption at 2600 A. The threedistinct peaks shown in Fig. 3 wereproduced by the 5'-, 2'-, and 3'-mono-phosphates. After passing through theultraviolet analyzer, the radioactivityin the eluant was monitored with theaid of a flow-cell scintillation counter(11). A second pen on the recordertraced the radioactivity. The radio-active trace coincided with that of theultraviolet absorption, showing thatmaterial identical with 5'-, 2'-. and 3'-nucleotides was synthesized from thestarting material, 14C-labeled cytidineand "2P-labeled phosphate.The sodium dihydrogen orthophos-phate was a reasonable choice as asource of phosphate for our first experi-ments since it may have been presenton the primitive earth. In subsequentexperiments, we used a numnber ofother sources of phosphorus which may

also have occurred on the prebioticearth. Among these were disodiummonohydrogen, trisodium, sodium am-monium monohydrogen, ammonium di-hydrogen, diammonium monohydrogen,monocalcium and tricalcium orthophos-phates, and phosphoric acid. In everycase monophosphates were formed. Acomparative study for uridine mono-phosphates is shown in Fig. 4. Table 1expresses the same result quantitatively.The second column gives the totalphosphate formed based on the per-centage of the uridine used. The pres-ence of a large amount of water ofcrystallization appears to lower theyields. However, the highest yield is inthe case of NaH,PO4 ?H.O which hadone molecule of water of crystallization.In order to assess the role of water,we studied the effect of added wateron the reaction. In the case of uridine(2 /1mole) and NaH.,PO, ?H,O (2pumole), the yield of 2'-, 3'-, and 5'-phosphates was not affected even withthe addition of 50 mniole f water, al-though the amount of cyclic phosphateformed decreased. When more waterwas added, the total yield diminished.In the presence of 500 ,umole of water,the reaction still took place, althoughthe yield was an order of magnitudeless.A study of the reaction at 160?Cover a 24-hour interval indicated that

I I I I50 75 100 125ml .02 N FORMIC ACID

Fig. 3. Cytidine 2P-monophosphates sep-arated on Dowex-1 formate column. Theslight shift in the radioactive trace is dueto the displacement of the second pen ofthe recorder.SCIENCE, VOL. 148

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CL l?;:::???;?::: j :ar:::i:::::::::i:::~l ii:~~itr~~::::??????I???:? ::: :?:i::::?:i iii~~il.. :,...,:...,.... ...... . ...:gg :;:?? :,::,

u .........~~~~?:;:::?.?r::::.. .;...???,?:::::ir?:::::i:::pC:'i::I::::":::::Liiljjii:li;LJjiiili~:il:::':::::i::,.:iii

)RIIGI URIDINE~~~~~~~~~~~~~~~~~~~~~~~~~~~~:::::ii~iii~i~fii~~i-::::?e?:;:~::!ilii::?i?ii~j~:::::::::?:::~::::L.r:?NaH2O4N2HP4 N0PO4 HAHPO4 NH4)HP0 H3P4 NaH4H04 C(H3P4)?Fig.. Autoradiograph showing reaction between "C-uridine and different sourcesof:~I''';jIiiphosphorus.lectrophoresis, of products at pH.5.::ii::::-ii8~i:~:~::~i:i:::::::t~i~.:~~:Sij~:~

CL l?;:::???;?::: j :ar:::i:::::::::i:::~l ii:~~itr~~::::??????I???:? ::: :?:i::::?:i iii~~il.. :,...,:...,.... ...... . ...:gg :;:?? :,::,

u .........~~~~?:;:::?.?r::::.. .;...???,?:::::ir?:::::i:::pC:'i::I::::":::::Liiljjii:li;LJjiiili~:il:::':::::i::,.:iii

)RIIGI URIDINE~~~~~~~~~~~~~~~~~~~~~~~~~~~~:::::ii~iii~i~fii~~i-::::?e?:;:~::!ilii::?i?ii~j~:::::::::?:::~::::L.r:?NaH2O4N2HP4 N0PO4 HAHPO4 NH4)HP0 H3P4 NaH4H04 C(H3P4)?Fig.. Autoradiograph showing reaction between "C-uridine and different sourcesof:~I''';jIiiphosphorus.lectrophoresis, of products at pH.5.::ii::::-ii8~i:~:~::~i:i:::::::t~i~.:~~:Sij~:~

the total monophosphate formed reacheda peak around 4 hours and remainedfairly constant, with a gradual declineafter 8 hours. After 2 hours, the cyclicphosphate was present in greateramount than the noncyclic. This estab-lished that some cyclization processwas taking place. The 2'-, 3'-, and5'- were perhaps being converted intocyclic forms. We have so far identifiedonly the cyclic 2',3'-monophosphates.The percentage yields of monophos-phate of different types of nucleosideswere adenosine, 3.1; guanosine, 9.8;cytidine, 13.7; uridine, 20.6; thy-midine, 6.3. Thus uridine monophos-phate was obtained in highest yield andadenosine monophosphate in lowest.The pyrimidine nucleosides gave higheryields than the purine nucleosides.We also have preliminary evidencefor the presence of dinucleoside phos-phates ApA, GpG, UpU, CpC, andTpT (A, adenosine; G, guanosine; C,cytidine; U, uridine; T, thymidine).Their presence was indicated by therelaitive rate of migration at pH 3.5 (6)and separation by paper chromatog-raphy with a mixture of 95 percent eth-anol and IM ammonium acetate (5:2by volume) (7). Further examination ofthis product is necessary before itsidentity can be definitely asserted. Thereis also an indication from the electro-phoretic migration that the nucleosidediphosphates and nucleoside triphos-phates are formed in this reaction.It has been successfully demonstratedthat methane, ammonia, and water can,by the action of various forms of energy,give rise to some of the constituents ofthe nucleic acid molecule and of theprotein molecule. Different solutionsto this problem have been proposed.Amino acids have been copolymerizedto give compounds of high molecularweight by heating them in the absence28 MAY 1965

the total monophosphate formed reacheda peak around 4 hours and remainedfairly constant, with a gradual declineafter 8 hours. After 2 hours, the cyclicphosphate was present in greateramount than the noncyclic. This estab-lished that some cyclization processwas taking place. The 2'-, 3'-, and5'- were perhaps being converted intocyclic forms. We have so far identifiedonly the cyclic 2',3'-monophosphates.The percentage yields of monophos-phate of different types of nucleosideswere adenosine, 3.1; guanosine, 9.8;cytidine, 13.7; uridine, 20.6; thy-midine, 6.3. Thus uridine monophos-phate was obtained in highest yield andadenosine monophosphate in lowest.The pyrimidine nucleosides gave higheryields than the purine nucleosides.We also have preliminary evidencefor the presence of dinucleoside phos-phates ApA, GpG, UpU, CpC, andTpT (A, adenosine; G, guanosine; C,cytidine; U, uridine; T, thymidine).Their presence was indicated by therelaitive rate of migration at pH 3.5 (6)and separation by paper chromatog-raphy with a mixture of 95 percent eth-anol and IM ammonium acetate (5:2by volume) (7). Further examination ofthis product is necessary before itsidentity can be definitely asserted. Thereis also an indication from the electro-phoretic migration that the nucleosidediphosphates and nucleoside triphos-phates are formed in this reaction.It has been successfully demonstratedthat methane, ammonia, and water can,by the action of various forms of energy,give rise to some of the constituents ofthe nucleic acid molecule and of theprotein molecule. Different solutionsto this problem have been proposed.Amino acids have been copolymerizedto give compounds of high molecularweight by heating them in the absence28 MAY 1965

of water (12). Dehydrations have alsobeen effected in dilute aqueous solu-tions (13). In our laboratory severalpossibilities have been studied-dryconditions, a dilute aqueous milieu, anenvironment with a relative absence ofwater, and reactions in contact withthe surface of a clay bed (14).We have presented the results ofreactions in an environment with a rel-ative absence of water. Since wateris not incompatible with this reactionand does not hinder it unless presentin large excess, the conditions underwhich the reaction proceeds may bedescribed as hypohydrous. The maxi-mum temperature was 160?C. Whereaswe obtain a yield of about 20 percentat that temperature in 2 hours, experi-ments at 80?C have given us a yieldof monophosphate of about 3 percentin 12 days. The 3 percent was made upof 2'-, 3'-, and 5'-monophosphates andcyclic 2',3'-phosphate. At this tempera-ture the yield of dinucleoside mono-phosphate was about 2 percent. At atemperature lower than 80?C the re-action may still take place, but at amuch slower rate. We do not know howcatalytic or surface reactions could ac-celerate this process. Preliminary evi-dence from our own experiments sug-gests that the surface of clay canpromote such a reaction. Our reportestablishes very clearly that the fivenucleotides present in RNA and DNAcan be prepared in good yield underconditions which may be consideredto be genuinely abiotic and which couldreasonably have existed on the primi-tive earth.

CYRIL PONNAMPERUMARUTH MACK

Exobiology Division, NationalAeronautics and Space Administration,Ames Research Center,Moffett Field, California

of water (12). Dehydrations have alsobeen effected in dilute aqueous solu-tions (13). In our laboratory severalpossibilities have been studied-dryconditions, a dilute aqueous milieu, anenvironment with a relative absence ofwater, and reactions in contact withthe surface of a clay bed (14).We have presented the results ofreactions in an environment with a rel-ative absence of water. Since wateris not incompatible with this reactionand does not hinder it unless presentin large excess, the conditions underwhich the reaction proceeds may bedescribed as hypohydrous. The maxi-mum temperature was 160?C. Whereaswe obtain a yield of about 20 percentat that temperature in 2 hours, experi-ments at 80?C have given us a yieldof monophosphate of about 3 percentin 12 days. The 3 percent was made upof 2'-, 3'-, and 5'-monophosphates andcyclic 2',3'-phosphate. At this tempera-ture the yield of dinucleoside mono-phosphate was about 2 percent. At atemperature lower than 80?C the re-action may still take place, but at amuch slower rate. We do not know howcatalytic or surface reactions could ac-celerate this process. Preliminary evi-dence from our own experiments sug-gests that the surface of clay canpromote such a reaction. Our reportestablishes very clearly that the fivenucleotides present in RNA and DNAcan be prepared in good yield underconditions which may be consideredto be genuinely abiotic and which couldreasonably have existed on the primi-tive earth.

CYRIL PONNAMPERUMARUTH MACK

Exobiology Division, NationalAeronautics and Space Administration,Ames Research Center,Moffett Field, California

References and Notes1. J. Oro, Ann. N.Y. Acad. Sci. 108, 464 (1963);C. Ponnamperuma, in The Origins of Pre-biological Systems, S. W. Fox, Ed. (Aca-demic Press, New York, 1965), p. 221.2. C. Ponnamperuma, R. Mariner, C. Sagan,Nature 198, 1199 (1963); C. Ponnamperumaand P. Kirk, ibid. 203, 400 (1964).3. C. Ponnamperuma, C. Sagan, R. Mariner,ibid. 199, 222 (1963); G. Steinman, R. M.Lemmon, M. Calvin, Proc. Natl. Acad. Sci.U.S. 52, 27 (1964); W. F. Neuman and M.W. Neuman, University of Rochester AECReport UR-656 (Rochester, N.Y., 1964).4. C. Ponnamperuma, P. Kirk, R. Mariner, B.Tyson, Nature 202, 393 (1964).5. Pherograph Nach Wieland-Pfleiderer, manu-factured by Wissenschaftliche Apparate, Hei-delberg, West Germany.6. J. D. Smith, in The Nucleic Acids, E.Chargaff and J. N. Davidson, Eds. (Aca-demic Press, New York, 1955), vol. 1, p.267.7. Procedure at pH 7.2 (6) modified.8. D. Brown, D. Magrath, A. Todd, J. Chem.Soc. 1952, 2708 (1952).9. L. Heppel, P. Ortiz, S. Ochoa, J. Biol.Chem. 680, 229 (1957).10. W. E. Cohn, in The Nucleic Acids, E.Chargaff and J. N. Davidson, Eds. (Aca-demic Press, New York, 1955), vol. 1, p.211.11. Nuclear-Chicago model 6350 Chroma-Cellequipped with 4-ml capacity flow cell.12. S. W. Fox, Science 132, 300 (1960).13. C. Ponnamperuma and E. Peterson, ibid.147, 1572 (1965); G. Steinman, R. M. Lem-mon, M. Calvin, ibid., p. 1574.14. J. D. Bernal, The Physical Basis of Life(Routledge and Kegan Paul, London, 1951);S. Akabori, in The Origin of Life on theEarth, F. Clark and R. L. M. Synge, Eds.(Pergamon, London, 1959), p. 189.

29 March 1965

Late Glacial Ice-Wedge Castsin Northern Nova Scotia,CanadaAbstract. Ice-wedge casts in northernNova Scotia and the relation of thecasts to the outwash that contains themindicate that the ice wedges formed in apermafrost environment after the ac-cumulation of the outwash. This perma-frost environment is tentatively corre-lated with pollen zolne L-3 of the GillisLake deposit, Cape Breton Island, NovaScotia, and with the Valders time ofthe midcontinental sequence.My observations indicate that thelast Pleistocene ice sheet to cover north-ern Nova Scotia dissipated primarily

by downwasting, probably by down-melting (1). When the crest of theCobequid Mountains (Fig. 1) becameexposed, the ice to the south betweenthe mountains and Minas Basin stag-nated and separated. Rivers of melt-water deposited valley trains south ofthe mountains. These valley trains

References and Notes1. J. Oro, Ann. N.Y. Acad. Sci. 108, 464 (1963);C. Ponnamperuma, in The Origins of Pre-biological Systems, S. W. Fox, Ed. (Aca-demic Press, New York, 1965), p. 221.2. C. Ponnamperuma, R. Mariner, C. Sagan,Nature 198, 1199 (1963); C. Ponnamperumaand P. Kirk, ibid. 203, 400 (1964).3. C. Ponnamperuma, C. Sagan, R. Mariner,ibid. 199, 222 (1963); G. Steinman, R. M.Lemmon, M. Calvin, Proc. Natl. Acad. Sci.U.S. 52, 27 (1964); W. F. Neuman and M.W. Neuman, University of Rochester AECReport UR-656 (Rochester, N.Y., 1964).4. C. Ponnamperuma, P. Kirk, R. Mariner, B.Tyson, Nature 202, 393 (1964).5. Pherograph Nach Wieland-Pfleiderer, manu-factured by Wissenschaftliche Apparate, Hei-delberg, West Germany.6. J. D. Smith, in The Nucleic Acids, E.Chargaff and J. N. Davidson, Eds. (Aca-demic Press, New York, 1955), vol. 1, p.267.7. Procedure at pH 7.2 (6) modified.8. D. Brown, D. Magrath, A. Todd, J. Chem.Soc. 1952, 2708 (1952).9. L. Heppel, P. Ortiz, S. Ochoa, J. Biol.Chem. 680, 229 (1957).10. W. E. Cohn, in The Nucleic Acids, E.Chargaff and J. N. Davidson, Eds. (Aca-demic Press, New York, 1955), vol. 1, p.211.11. Nuclear-Chicago model 6350 Chroma-Cellequipped with 4-ml capacity flow cell.12. S. W. Fox, Science 132, 300 (1960).13. C. Ponnamperuma and E. Peterson, ibid.147, 1572 (1965); G. Steinman, R. M. Lem-mon, M. Calvin, ibid., p. 1574.14. J. D. Bernal, The Physical Basis of Life(Routledge and Kegan Paul, London, 1951);S. Akabori, in The Origin of Life on theEarth, F. Clark and R. L. M. Synge, Eds.(Pergamon, London, 1959), p. 189.

29 March 1965

Late Glacial Ice-Wedge Castsin Northern Nova Scotia,CanadaAbstract. Ice-wedge casts in northernNova Scotia and the relation of thecasts to the outwash that contains themindicate that the ice wedges formed in apermafrost environment after the ac-cumulation of the outwash. This perma-frost environment is tentatively corre-lated with pollen zolne L-3 of the GillisLake deposit, Cape Breton Island, NovaScotia, and with the Valders time ofthe midcontinental sequence.My observations indicate that thelast Pleistocene ice sheet to cover north-ern Nova Scotia dissipated primarily

by downwasting, probably by down-melting (1). When the crest of theCobequid Mountains (Fig. 1) becameexposed, the ice to the south betweenthe mountains and Minas Basin stag-nated and separated. Rivers of melt-water deposited valley trains south ofthe mountains. These valley trainsmerged into outwash fans where thevalleys broadened and into deltas wherethe outwash reached the sea.Casts of ice wedges are common inthe outwash and are particularly well-

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merged into outwash fans where thevalleys broadened and into deltas wherethe outwash reached the sea.Casts of ice wedges are common inthe outwash and are particularly well-1223