A number of theories propose that RNA, or an RNA-like substance, played a role in the origin of life. Usually, such hypotheses presume that the Watson–Crick bases were readily available on prebiotic Earth, for spontaneous incorporation into a replicator. Cytosine, however, has not been reported in analyses of meteorites nor is it among the products of electric spark discharge experiments. The reported prebiotic syntheses of cytosine involve the reaction of cyanoacetylene (or its hydrolysis product, cyanoacetaldehyde), with cyanate, cyanogen, or urea. These substances undergo side reactions with common nucleophiles that appear to proceed more rapidly than cytosine formation. To favor cytosine formation, reactant concentrations are required that are implausible in a natural setting. Furthermore, cytosine is consumed by deamination (the half-life for deamination at 25°C is ≈340 yr) and other reactions. No reactions have been described thus far that would produce cytosine, even in a specialized local setting, at a rate sufficient to compensate for its decomposition. On the basis of this evidence, it appears quite unlikely that cytosine played a role in the origin of life. Theories that involve replicators that function without the Watson–Crick pairs, or no replicator at all, remain as viable alternatives.

Among the most commonly encountered ideas concerning the origin of life is the one that it involved an “RNA world” at an early stage (1). The term was coined by Gilbert (2), who also stated “The first stage of evolution proceeeds, then, by RNA molecules performing the catalytic activities necessary to assemble themselves out of a nucleotide soup.” The existence of such a soup has generally been taken for granted. For example, Eigen and Schuster (3) wrote “The building blocks of polynucleotides—the four bases, ribose and phosphate were available too under prebiotic conditions. Material was available from steadily refilling pools for the formation of polymers, among them polypeptides and polynucleotides.” The experimental evidence to date, however, does not appear to support such claims.

Many problems have arisen with both the prebiotic synthesis and the stability of ribose (4–9). To avoid the need for ribose, some authors have preferred to invoke an RNA-like polymer, with a simpler or more accessible backbone, at the start of life (6, 10–16). A pre-RNA world would have come first, during which some substance of this type carried out the genetic functions later taken over by RNA. In the great majority of these theories, Watson–Crick pairing of A with U and of G with C is retained as the basis of genetic template recognition.

These suggestions still presume that the bases adenine, cytosine, guanine, and uracil were readily available on early Earth. I have argued that this presumption is not supported by the existing knowledge of the basic chemistry of these substances (4, 17). If the availability of the Watson–Crick pairs at the start of life appears implausible, then more attention must be given to theories that employ a very different replicator or no replicator at all.

To provide a firm basis for this conclusion, I have undertaken a series of reviews in which I consider in detail the chemical evidence for the availability of the Watson–Crick bases at the start of life. In a previous paper, however, I concluded that current information concerning the availability and chemical properties of adenine did not support the idea that it was used in a replicator at the start of life (17). In this publication, I wish to consider the prebiotic syntheses and the stability of cytosine.


RESULTS AND DISCUSSION

Absence of Cytosine in Meteorites and Electrical Spark Discharge Experiments. The isolation of adenine and guanine from meteorites has been cited as evidence that these substances might have been available as “raw material” on prebiotic Earth (18). However, acid hydrolyses have been needed to release these materials, and the amounts isolated have been low (17–19). Traces of uracil have also been reported in such analyses (20), but no cytosine at all.
The formation of a substance in an electric spark discharge conducted in a simulated early atmosphere has also been regarded as a positive indication of its prebiotic availability (21). Again, low yields of adenine and guanine have been reported in such reactions, but no cytosine (22). The failure to isolate even traces of cytosine in these procedures signals the presence of some problem with its synthesis and/or stability.

Proposed Prebiotic Cytosine Syntheses. As bonds from carbon to a hetero atom are more readily constructed than carbon–carbon bonds, cytosine syntheses have usually combined a three-carbon fragment with another bearing a urea-like carbon. The most prominent C-3 fragments used have been cyanoacetylene and its hydrolysis product, cyanoacetaldehyde. These processes are discussed separately below.
Syntheses based on cyanoacetylene. As shown in Fig. 1(Fig. 1), Ferris et al. (23) reported that 0.2 M cyanoacetylene (I) and 2 M cyanate (II) reacted together readily at 30°C to give trans-cyanovinylurea (III) and unidentified products. Conversion of trans-cyanovinylurea to cytosine (with the cis isomer as a likely intermediate) took place readily at pH 11 or greater. In a more direct preparation, cyanate and cyanoacetylene were heated together at 100°C for 24 hr. In a typical run at low concentration, 0.025 M cyanoacetylene and 0.05 M cyanate (the stoichiometry requires two cyanates per cyanoacetylene) afforded 6% cytosine. The maximum yield observed over all circumstances was 19%.

View larger version:
In this page In a new window
Download as PowerPoint Slide
Figure 1 Principal proposed prebiotic routes to cytosine. The hydrolysis products of the reactants and of cytosine are included in the scheme.
Questions arise, however, concerning the availability of the reactants on early Earth. Cyanoacetylene can be produced in a spark discharge in a CH4/N2 mixture as the second most prevalent product (up to a maximum of 8.4% of the principal product, HCN) (23, 24). This mixture, which introduces carbon in reduced form but excludes ammonia and water, is an unlikely candidate for Earth’s atmosphere at the time of the origin of life. That atmosphere was “… probably dominated by CO2 and N2, with traces of CO, H2, and reduced sulfur gases”, unless a volcanic source of methane and ammonia was present (25). By contrast, when ammonia (24) or hydrogen sulfide (26) are included in spark discharge experiments, little cyanoacetylene is produced. The aspartic acid and asparagine that are formed under those conditions arise to some extent from the reaction of cyanoacetylene with HCN and ammonia (27).

An extensive solution chemistry for cyanoacetylene with simple nucleophiles has been recorded. Ammonia (28), amines (29–30), thiols (31), HCN (32), and “the commonly used alkaline buffers” (23), react rapidly at room temperature or lower with cyanoacetylene. In certain cases, e.g., the reaction of cyanoacetylene with phosphate, the product hydrolyzes to afford cyanoacetaldehyde (Fig. 1, IV) (33). But for many reactions of cyanoacetylene, the products appear stable or react further to afford further transformation products. The rates of reaction of cyanoacetylene with simple nucleophiles appear more rapid than its reaction with cyanate, but no direct competition experiments have been reported. In the absence of other nucleophiles, cyanoacetylene is hydrolyzed by water to cyanoacetaldehyde. The half-life at pH 9 and 30°C has been estimated as about 11 days (0.03 yr) (34).

The prebiotic availability of cyanate also is undetermined. It can be produced by hydrolysis of cyanogen (23), a simple substance that may be widely distributed elsewhere in the universe, as it has been detected in the atmosphere of Titan (35), and related nitriles are prominent components of interstellar clouds (36). No simulations have been carried out to estimate the formation of cyanogen under plausible early Earth conditions, however. Cyanogen’s stability in aqueous solutions is limited because it is decomposed by both base and acid. At 25°C and pH 9 (the usual pH for HCN oligomerization), cyanogen’s half-life can be estimated from existing data (37) to be less than 30 sec. Cyanogen or cyanoformamide (an intermediate hydrolysis product of cyanogen) can replace cyanate in its reaction with cyanoacetylene, affording cyanovinylurea at lower yields. At pH 8 and room temperature (9 days reaction time, 0.1 M reactants), yields of cyanovinylurea were 2.9% from cyanoformamide, 3.0% from cyanogen, and 4.7% from cyanate.

Small amounts of ammonium cyanate also exist in equilibrium with urea (ref. 38, and see below) but these quantities would appear insufficient for the synthesis. A reaction of 1 M urea with 1 M cyanoacetylene (100°C, 20 hr) afforded 4.8% cytosine, but no cytosine was detected when reagent concentrations were reduced to 0.1 M (23). Much higher concentrations of urea than of cyanate are needed for cytosine synthesis. Urea might have been more available than cyanate on prebiotic Earth, however, as its formation in electric discharge experiments under an atmosphere of N2, CO, and H2O has been reported (39).

Apart from the questions concerning its availability, cyanate is unstable in aqueous solution, hydrolyzing to ammonium carbonate with a half-life of “… at most a hundred years” (23). For these reasons, the authors concluded that “it is difficult to see how concentrations (of cyanate and cyanoacetylene) as high as 0.01 M could have accumulated in the primitive ocean.”

Syntheses based on cyanoacetaldehyde. The synthesis of cytosine from cyanoacetaldehyde (Fig. 1, IV) and urea (V) was reported by Robertson and Miller (40). The authors described this reaction in the following terms. “Here we show that in concentrated urea solution—such as might have been found in evaporating lagoons or in pools on drying beaches on early Earth—cyanoacetaldehyde reacts to form cytosine in yields of 30–50%, from which uracil can be formed by hydrolysis… The previous lack of plausible prebiotic syntheses of cytosine and uracil has led some other authors to suggest that other bases were used in the first genetic material. These reactions provide a plausible route to the pyrimidine bases required in the RNA world.” This reaction is closely related to the synthesis of cytosine from cyanoacetylene and urea (23) described above. Robertson and Miller (40) noted this in a correction: “Replacing cyanoacetylene by its hydrolysis product cyanoacetaldehyde gives essentially the same yield, suggesting that the cyanoacetylene reaction may have gone through cyanoacetaldehyde.”
The Robertson-Miller procedure was conducted by heating 10−3 M cyanoacetaldehyde with varying urea concentrations (expressed as molality) in a sealed ampule at 100°C. For kinetic purposes, the reaction was stopped after 5 hr. The rate equation contained first-order and second-order terms in urea. The half-life in 1 molal urea can be calculated from their equation as 180 hr. In 10 molal urea, it is 67 hr. The maximum yield was determined from much longer runs and expressed as the sum of uracil (formed by deamination) and cytosine. This sum rose sharply with urea concentration at low concentration (about 20% in 5 molal urea) and then leveled off to about 33% in 20 molal urea. The yield of cytosine alone, reported only for a reaction run in saturated urea (120 molal), was 53%. An Arrhenius plot of their data gave a heat of activation of 28.2 kcal (1 cal = 4.18 J). At 25°C, the half-life would be 300 yr with 1 M urea and 15 yr with 20 molal urea (the maximum concentration attainable at that temperature).

An obvious difficulty with this reaction is that the formation of cytosine and the subsequent deamination of the product to uracil (see below) occur at the about the same rate when urea concentrations are 1–2 M. Robertson and Miller (40) noted that 40% of cytosine was deaminated after 120 hr at 100°C and that in saturated urea, cytosine yields fell after 30 hr because of deamination. It is clear that the yield of cytosine would fall to 0% if the reaction were extended for a number of half-lives. This provides no difficulty in the laboratory, where one can start with a urea concentration of one’s choice and monitor the time carefully. On early Earth, the following circumstances would be needed: An isolated lagoon or other body of sea water would have to undergo extreme concentration, to perhaps 10−5 of its initial volume. This reduction in volume would be needed to bring urea from a concentration of 10−4 to 10−5 M assumed for many substances in a prebiotic ocean (see below) to that necessary for the reaction. It would further be necessary that the residual liquid be held in an impermeable vessel, for reasons described below. The concentration process would have to be interrupted for some decades (assuming a temperature near 25°C) with the urea concentration near saturation, to allow the reaction to occur. At this point, the reaction would require quenching (perhaps by evaporation to dryness) to prevent loss by deamination. At the end, one would have a batch of urea in solid form, containing some cytosine (and uracil). This sequence cannot be excluded as a rare event on early Earth, but it cannot be termed plausible.

The above circumstances do not provide the only barrier to the success of the reaction. Questions arise about the availability of cyanoacetaldehyde. Browne (41) termed it “… another quite common component of sea water that owes its formation partly to lightning bolts.” Robertson and Miller (40) justify its prebiotic availability as a hydrolysis product of cyanoacetylene, which in turn is “… produced from a spark discharge in a CH4/N2 mixture [23, 24] and is an abundant interstellar molecule.” As we have explained above, however, the questionable availability of cyanoacetylene and its reactivity to a broad variety of common nucleophiles make it an unreliable source for cyanoacetaldehyde.

Cyanoacetaldehyde also is vulnerable to reaction with a number of chemicals considered to be prebiotic. Its reaction with cyanide has been described theoretically (42), although it apparently has not carried out experimentally. Cyanoacetaldehyde is in equilibrium with a dimer (23), which then reacts readily with thiols (43). Its reaction with amino groups of proteins (44) suggests that simple amino acids will also combine with it. The great chemical activity exhibited by both cyanoacetaldehyde and its precursor suggest that little of either will persist in prebiotic media, even before the start of a concentration process. The synthesis of Robertson and Miller (40) was carried out with the exclusion other possible prebiotic chemicals that might have interfered. Furthermore, no experiments were reported to assess the effect of concentrated brine (expected from the evaporation of seawater) on the synthesis.

In the case of cyanoacetaldehyde, however, one disruptive chemical could not be excluded: water. Although it is more stable than its precursor, cyanoacetaldehyde is subject to hydrolysis to acetonitrile and formate, with a half-life of 31 yr at 30°C and pH 9 (34). This rate makes the reaction competitive with cytosine formation at the lower end of the range of urea concentrations studied (40). When a combination of 0.1 M urea and 0.1 M cyanoacetaldehyde were heated together earlier by other workers (34), no pyrimidines were detected. We deduced earlier that an extreme concentration process (to about 1:105) was necessary to bring urea to a concentration suitable for reaction with cyanoacetaldehyde. But unless that concentration took place very rapidly (years, not decades) on a geologic time scale, any initial cyanoacetaldehyde would be unlikely to survive the process.

Urea would also be at risk during a lengthy evaporative process. It exists in equilibrium with a small amount of ammonium cyanate (K e at 60°C = 1.04 × 10−4) (38). This equilibrium will be shifted to the right continually by further hydrolysis of cyanate to carbonate and (in an open system) escape of ammonia. The cytosine synthesis of Robertson and Miller was carried out in a sealed tube, which prevented ammonia loss. The rate constant for urea decomposition at 60°C is 2.6 × 106⋅s−1 and the half-life is 30 days. The half-life at 25°C has been estimated at 25 yr (27). This is comparable with the rate of cytosine synthesis in concentrated urea solutions, but of course decomposition could take place during the concentration phase as well. Other substances likely to be present on early Earth could also consume the urea during the concentration process. When 0.1 M glycine and 0.1 M urea are heated together in a sealed tube at 100°C for 10 hr, >50% of the glycine is converted to N-carbamoyl glycine. The carbamoylating agent is cyanate, formed from the urea (45). When a similar reaction was run in an open system to facilitate ammonia loss, half of the urea was destroyed after 5 hr at 90°C and pH 7 (46). Diglycine, oligoglycines, and diketopiperazines were other reaction products. These reactions appear more rapid than cytosine synthesis and take place at lower urea concentrations. Unless amines and amino acids were excluded, they would presumably prevent cytosine synthesis.

The combination of circumstances described above limits the cytosine synthesis from urea and cyanoacetaldehyde to circumstances in which concentrated urea can be employed from the beginning, competing nucleophiles can be excluded, and the time can be controlled carefully.

Deamination of Cytosine. As we saw in the previous section, the spontaneous deamination of cytosine and its derivatives in aqueous solutions provides an obstacle in prebiotic preparations of these substances. This reaction was first reported from our own laboratories (47–48). It takes place at a sufficient rate in single-stranded DNA for it to constitute a genetic hazard (49–50). Cells are normally protected from the reaction by the repair enzyme, uracil-DNA glycosylase, but in the absence of that enzyme, enhanced mutagenesis occurs (51).
The most detailed studies of the deamination of cytosine and cytidine have been carried out by Garrett and Tsou (52). They reported that the reaction occurs at all pH values but is minimal in the range 6–9. Acid catalyzes the reaction by protonation of cytosine, and base speeds it by direct attack on cytosine. A variety of buffers also catalyze the reaction (47, 52) with bisulfite having a particularly strong effect (53–54). The data of Garrett and Tsou have recently been extended by Levy and Miller (55), who estimated, by extrapolation, a half-life of 340 yr at pH 7 and 25°C for cytosine (uncatalyzed reaction). This corresponds to a rate of 6.5 × 10−11⋅s−1. This rate was increased by common buffers, for example, by 50% in 0.05 M acetate. The value is roughly compatible with those calculated by others for the deamination of cytidine and single-stranded DNA (49, 56–58). The activation energy reported in these studies is in the range of 26–29 kcal/mol.

This situation was summarized some years ago: “Cytosine hydrolyzes to uracil rather rapidly and cytidine is hydrolyzed to uridine at a similar rate… This is a real difficulty if it is assumed that cytosine was required for nucleic acids in the first organism.” (27).

Deamination, of course, is not the only hazard; other chemical reactions will also deplete cytosine supplies. For example, exposure to solar UV light on early Earth would quickly convert cytosine to its photohydrate and to cyclobutane photodimers (both very susceptible to deamination) (59). Such reactions would place an additional requirement on prebiotic cytosine syntheses: they must be carried out in the dark.

Prebiotic Plausibility of Cytosine Synthesis. The assembly of a cytosine-containing replicator would require several steps beyond cytosine synthesis as well as the concurrent synthesis of the other replicator components. We wish to consider the suitability of the reactions described above for the prebiotic synthesis of cytosine, not in trace amounts but in the quantities needed to support further chemical transformations. We must assume that prebiotic cytosine synthesis took place at a rate that replaced the material lost by deamination, to maintain a steady-state concentration. The synthetic requirements depend on the assumptions made about the environment in which the replicator was assembled.
Synthesis in a global ocean. This concept underlies the Oparin-Haldane hypothesis, a central paradigm of the origin-of-life field (see ref. 27 for a comprehensive list of references). In this account, the origin of life took place in such an ocean, sometimes termed “the prebiotic soup.” Possible concentrations for a number of substances such as adenine, ammonia, HCN, and total amino acids in a prebiotic ocean have been estimated and fall in the range from 10−5 to 10−4 M. (21, 60–61). Although an adenine concentration in this range has been considered as possibly too low for useful prebiotic synthesis (21), we will assume that a steady-state concentration of 10−5 M will suffice. We can then ask what rate of synthesis is needed to maintain a 10−5 M cytosine concentration in the soup?
If we use the data of Levy and Miller (55) at 25°C at pH 7, with dilute buffer catalysis (and excluding bisulfite), the rate of cytosine deamination is 10−10⋅s−1 × 10−5 M = 10−15 M⋅s−1. Cytosine has not been reported as a direct product of atmospheric processes, so we will assume that it is made by the reactions of two substances, A and B, that are produced globally and occur in the soup at a concentration of 10−5 M. The rate constant, K syn, for this reaction must be sufficient so that the cytosine produced balances that lost by deamination. (The synthetic reaction, of course, is second-order, whereas the deamination of cytosine is pseudo-first-order.) We then get

Solving to find the needed rate constant, we find that K syn = 10−5 M−1⋅s−1 at 25°C. A reaction with this rate constant should be readily demonstrable in the laboratory at 25°C. If A and B were at an initial concentration of 1 M, they should react to the extent of 10% in about 3 hr. Note that in this estimate, we have assumed neutral pH to minimize deamination. We have also ignored the possibility that A and B react with other substances present in the soup. In practice, the required K syn is likely to be higher. The reactions described above for prebiotic cytosine synthesis did not meet this requirement. They required reaction times of hours at 100°C. In the case of the cyanoacetaldehyde–urea combination, reaction at 25°C would require hundreds of years.

It has been argued that a cold or frozen condition for early Earth would be more favorable for the origin of life, as it would slow the decomposition of cytosine and the other bases (55). It is not obvious that any advantage would be gained by this, however, as the rate of the synthetic reaction would also be slowed on a frozen Earth. A careful study of the temperature profiles of the competing synthetic and degradative reactions would be needed to determine whether any significant advantage can be obtained by manipulating the reaction temperature.

Of course, some new combination of chemicals and an appropriate set of conditions may yet be encountered that would produce cytosine at the needed rate. This possibility seems unlikely, because the combinations of substances that may be present in the soup and react to form cytosine are limited and have already been explored to some extent.

The “drying lagoon” scenario. This term was used by Robertson and Miller (40) to describe processes in which reactants are concentrated in specific geologic environments such as lagoons, thereby enhancing their reaction rates. Very different environments could be used to synthesize the different replicator components. After synthesis, the components would be released into the open ocean, where final assembly could take place. As the purine and pyrimidine components of a replicator would be prepared in different environments, the replicator synthesis would take place in the open ocean. [This idea was attributed to Robertson and Miller by Browne (41)].
In this scenario, the concentrations of A and B could be enhanced greatly by concentration in a drying lagoon or comparable locale. For example, if A and B were both at 1 M, the rate would be enhanced by 1010, and a smaller value for K syn might suffice. However, this gain in rate would be largely overcome by the effects of the subsequent dilution. Deamination would take place on a global scale, but synthesis only within a limited locale. The available evidence suggests that volcanic islands constituted the principal land areas on early Earth, with the continents much smaller than their present size (62). If this were the case, then much less shoreline would be available for lagoon formation. No firm data exists concerning the extent of the ocean and the distribution of drying lagoons on early Earth, however, so we will use current information for our estimate. The volume of the oceans at present is 1.3 × 1018 m3 (63). A typical large lagoon such as the Sivash (Crimea) or the McLeod Evaporite Basin (western Australia) may hold 2 × 109 m3 of water (64–65). If we compare the initial volume of the vessel in which synthesis is to be carried out with that of the one available for deamination, we see that the latter exceeds the former by 6 × 108. Thus, the dilution factor dissipates much of the advantage produced by concentration of reactants.

EVOLUTIONARY SCENARIO FOR THE ORIGIN OF LIFE

The textbook11, 12 or standard materialistic scenario for the origin of life begins shortly after Earth’s formation. The earth in its primordial state was markedly different than today. Evolutionary researchers take advantage of the lack of certainty about Earth’s early conditions by postulating that reducing gases—hydrogen-rich gases such as ammonia, methane, and water vapor—made up the early earth’s atmosphere. They speculate that no oxygen was present. Under these conditions energy discharges, such as lightning, propagating through the early earth’s atmosphere would lead to the production of small organic molecules, such as formaldehyde and hydrogen cyanide.

According to this scenario, these prebiotic molecules would then accumulate in the earth’s oceans over vast periods of time to form the legendary primordial or prebiotic soup. Within the prebiotic soup, again over long periods of time, the small prebiotic molecules would react to form more complex molecules, such as amino acids, sugars, fatty acids, purines, and pyrimidines. These molecules would in turn function as building blocks for the complex molecules that eventually would lead to the biomolecules found in living systems today.

This explanation for the origin of life requires that the chemical reactions taking place in the prebiotic soup eventually produce molecules with the ability to self-replicate. As their concentration increased in the prebiotic soup, the large, complex molecules would be expected to aggregate to form protocells or prebionts. Over time, through random chemical and physical events, the self-replicating molecules found in the chemical aggregates would transfer this capability to the prebionts. Evolutionary processes (e.g. natural selection) would eventually lead the prebionts to become increasingly efficient self-replicators and increasingly more complex.

Finally these prebionts would yield an organism referred to as the last universal common ancestor (LUCA). LUCA presumably resembled a modern bacterium. LUCA, then, would have given rise to the major domains of life.

Table I lists some of the most important predictions that reasonably follow from the textbook origin-of-life scenario.

TABLE I
Some Predictions Made by the Naturalistic (Evolutionary) Origin-of-life Scenario

Chemical evidence for the prebiotic soup will be found in the geological record.
Placid chemical and physical conditions existed on the early earth for long periods of time.
Chemical pathways leading to the formation of biomolecules will be found.
Chemical pathways that produce biomolecules would have been capable of operating under the conditions of the early earth.
Life emerged gradually over a long period of time.
Life originated only once.
Life in its minimal form is simple.

BIBLICAL MODEL FOR THE ORIGIN OF LIFE

Genesis 1:2 provides the starting point for the biblical description of life’s beginnings:

Now the earth was formless and empty, darkness was over the surface of the deep, and the spirit of God was hovering over the waters.

This passage describes the earth in its primordial state.13 According to the text, the Spirit of God was moving above the surface of the waters, so the context of this passage is the earth’s surface. Positioned on the earth’s surface, a hypothetical observer would experience only darkness. He would also note that Earth’s surface was covered entirely with water. An observer would also see Earth as unsuitable for life. The Hebrew word translated as formless, tohu, connotes a desolate wasteland.14

The Genesis 1:2 description of the earth’s primordial conditions finds remarkable agreement with the scientific description of the earth’s initial conditions.

The interplanetary debris of the early solar system and thick primordial atmosphere of early Earth would keep sunlight from reaching its surface.15 Darkness would, indeed, be pervasive on the planet. While scientists debate the mechanism and timing for the formation of the earth’s oceans, consensus holds that continents did not exist when the earth formed. Early in its history Earth was, indeed, a water world.16 From the time of its formation (approximately 4.55 billion years ago) until 3.5 billion years ago, the earth experienced numerous collisions that would have rendered the earth a desolate planet largely unsuitable for life.17

Genesis 1:2 also describes the supernatural creation of the first life on Earth.18 The original language makes even more apparent than the English that the Spirit of God is doing more than simply hovering over the surface of the waters. The Hebrew word translated as “hovering,” rahap, may also be translated as “brooding.” In its only other biblical use, rahap describes the Spirit of God “protecting” the wandering nation of Israel (Deuteronomy 32:10-11):

In a desert land he found him, in a barren and howling waste. He shielded him and cared for him; he guarded him as the apple of his eye, like an eagle that stirs up its nest and hovers (rahap) over its young, that spreads its wings to catch them and carries them on its pinions.

Transposing this imagery onto Genesis 1:2, we see the Spirit of God “brooding” over the surface of Earth as a mother eagle, hatching and jealously protecting her young.19 As an added note, the nation of Israel is seen wandering in a land of desolation. Here, tohu is translated as howling waste, further linking Deuteronomy 32:10-11 and Genesis 1:2.


Life appeared early in Earth’s history.
Life appeared under harsh conditions.
Life miraculously persisted under harsh conditions.
Life arose quickly.
Life in its minimal form is complex.

RECENT SCIENTIFIC DISCOVERIES IN ORIGIN-OF-LIFE RESEARCH

Comparing the predictions made by the two origin-of-life scenarios with the record of nature provides the best means of assessing the validity of the two competing models. Some of the most recent breakthrough discoveries in origin-of-life research specifically address predictions made by the two models.

TIMING OF LIFE’S APPEARANCE

Origin-of-life researchers have recently uncovered unequivocal evidence that life first appeared early in Earth history, shortly after the formation of the first rocks.20-23 The oldest rocks yet discovered on Earth date at around 3.9 billion years old. Prior to this time, the earth existed largely in a molten state unsuitable for life. Researchers have identified carbonaceous deposits—deposits made up of carbon compounds such as kerogen tars, graphite and apatite—from the earth’s oldest rocks, dated at 3.86 billion years old. The chemical signature of these carbonaceous deposits indicates that they were produced as the by-product of biological activity. Fully consistent with the discovery of life’s by-products from 3.86 billion years ago is the discovery of fossilized bacteria in rocks about 3.5 billion years old.24, 25

CONDITIONS AT THE TIME OF LIFE’S APPEARANCE

Life first appeared and spent its early existence under unimaginably harsh conditions. In scientific terms, it should not have originated, let alone persisted. From the time of Earth’s formation (at 4.55 billion years ago) until around 3.9 billion years ago, the planet experienced frequent impacts.26, 27 Some of the objects (asteroids, comets, and planetesimals) striking the earth were approximately 100 km in diameter. Upon impact, these colliders liberated so much energy that, not only did water on the earth’s surface become volatilized, but rocks on the surface and subsurface melted. The giant impactor phase of Earth’s history ended around 3.9 billion years ago. However, at this time, gravitational perturbation in the solar system caused objects in the Kuiper-Edgeworth belt to rush toward the inner solar system.28 This event, termed the late heavy bombardment, led to over 17,000 collisions with the earth, destroying any life that would have been present. Finally, between 3.9 billion years ago and 3.5 billion years ago impactors still collided with the earth, though the size and frequency of impact diminished with time.29 Many of these events still would have vaporized the earth’s oceans, leading to a wholesale destruction of life. Between 3.9 and 3.5 billion years ago, multiple origin-of-life events must have taken place with the maximum time window between impact events, and hence for the origin of life, being 10 million years.30

SOUP OR NO SOUP?

To date, origin-of-life researchers have failed to recover any geochemical remnants of prebiotic molecules—organic molecules produced by nonbiological processes. 31 All the carbonaceous deposits recovered from the oldest rocks are, without exception, the by-product of biological activity. The “absence of evidence” for a prebiotic soup must be taken as “evidence of absence.”32

If a prebiotic soup was not present on the early earth, the existing conditions would not support the formation of prebiotic molecules. Conversely, if it is discovered that the conditions of early Earth were not conducive to the formation of prebiotic molecules, a prebiotic soup would not be found within the geological record.

Fitting with the lack of evidence for a prebiotic soup is the growing recognition that the early earth’s conditions would not have supported the synthesis of prebiotic molecules. For example, mounting evidence indicates that the early earth’s atmosphere was neutral, not reducing, composed of N2, CO2, and H2O.33, 34 Even with the absence of O2 (an inhibitor to the process of forming life molecules), prebiotic molecules cannot be produced in this type of atmosphere.35, 36 Strong evidence also has emerged that there were low, but significant levels of O2 not only in the early earth’s atmosphere, but also in the early earth’s hydrosphere.37-39 The presence of O2 would serve to inhibit the formation of prebiotic molecules.

VIABILITY OF CHEMICAL PATHWAYS TO LIFE

The prebiotic soup predicted by the textbook evolutionary model did not exist on early Earth. However, even if it had existed, it could not have led to life’s beginning. Origin-of-life researchers have discovered a number of chemical routes capable of yielding many of the molecules needed to build life,40 but abiotic pathways to many other crucially important classes of biochemical compounds have yet to be discovered and may not even exist.41

Even more problematic for the naturalistic origin-of-life scenario is the recognition that the conditions of the hypothetical primordial soup and of the early earth would have inhibited most, if not all, potential prebiotic chemical routes. Many of the potential prebiotic reactions can only succeed under restrictive conditions. In most cases, it is unlikely that these conditions existed on the early earth. In some instances, the same conditions needed to drive the formation of biochemical compounds would have led to their subsequent destruction.42, 43

New evidence indicates that the transition metals and rare earth elements in the early earth’s oceans would have promoted the decomposition of what many scientists believe were key intermediate chemical compounds taking part in the most widely accepted evolutionary origin-of-life scenarios.44 The hypothetical primordial soup would have undoubtedly been a complex chemical mixture comprised of a large number of chemical species. The same chemical routes that would have led to the production of biochemical compounds under laboratory conditions would have been inhibited by other components in the primordial soup. These interfering compounds would have either terminated or redirected key steps in the prebiotic pathways.45, 46 Given the likelihood of widespread chemical interference in the hypothetical primordial soup, the success of origin-of-life researchers in preparing biochemical compounds is a false success. Origin-of-life investigators typically study potential prebiotic pathways under unrealistic, controlled, chemically pristine conditions.

SIMPLICITY OR COMPLEXITY OF FIRST LIFE?

New evidence indicates that life in its minimal form is chemically complex even if morphologically simple. The smallest bacterial genomes capable of independent survival include between 1500-1900 gene products.47-50 These bacteria are believed to be the oldest organisms on Earth and quite likely reflect the complexity of first life on Earth and the minimum complexity of independent life.51 The smallest known genome, that of Mycoplasma genitalium, is comprised of 470 gene products.52 However, M. genitalium is not an appropriate model for the origin of life, for it depends on host biochemistry to survive and, therefore, cannot exist independently. Nonetheless, M. genitalium is a good model for determining the bare minimum requirements for life. Theoretical and experimental work using M. genitalium indicate that life requires at least 250-350 gene products (having eliminated, in theory, genes used for parasitic interactions).53-55

Biophysicist Hubert Yockey has calculated the probability of forming a single gene product (one that is functionally equivalent to the ubiquitous protein cyctochrome C) as one chance in 1075. 56 Given this probability, Yockey calculated that if the hypothetical primordial soup contained about 1044 amino acids, a hundred billion trillion years would yield a 95% chance for random formation of a functional protein only 110 amino acids in length (a single gene product).57 The universe is about 15 billion years old. This means that less than one trillionth of the time has passed that would be needed to make even one of the 250-350 gene products necessary for minimal life, or one of the 1500 gene products necessary for independent life.

Further complicating the supra-astronomical probabilities that must be overcome for even the simplest life to arise by natural processes is the changing view of bacteria. No longer regarded as cells with a random, nondescript internal structure, bacteria are now recognized as having remarkable internal organization, both spatially and temporally, at the protein level.58, 59 This internal organization of bacterial cells is universal and is needed for their survival. This means that origin-of-life researchers must account for not only the simultaneous appearance of 250-350 gene products but also their organization inside the cell.

BIBLICAL DESCRIPTION AGREES WITH SCIENTIFIC DISCOVERIES

Comparing the predictions of the biblical origin-of-life model with the most recent discoveries coming from origin-of-life research reveals remarkable agreement. Life originated early and quickly in Earth’s history under hostile conditions. Moreover, life as it first appeared, in its minimal form, possesses enormous complexity.

None of the predictions that come from the naturalistic model are satisfied by the most recent scientific results. From a naturalistic perspective, supra-astronomical probabilities argue against the required simultaneous assembly of the molecular components needed for life to function in its most minimal form. Perhaps most devastating of all is the absence of a primordial soup on early Earth. All origin-of-life models that appeal exclusively to natural processes have as their chief requirement a primordial soup. Even if a primordial soup existed, however, the chemical processes supposedly taking place in the soup seem incapable of producing life. In light of the most recent scientific discoveries, the comments of Paul Davies and the quiet frustration of origin-of-life researchers seem understandable.

The harmony between the Bible’s account of the origin of life and nature’s record provides powerful evidence for the validity of the Christian faith. The lack of concordance between the naturalistic model for life’s origin and the scientific data causes one of the key pillars of the theory of evolution to crumble. Once a reasonable, testable case has been made for the supernatural origin of life, the door is open to view other areas of the biological realm from a supernatural standpoint as well.

In addition to demonstrating the truthfulness of Scripture, recent discoveries show how the biblical account of origins can contribute to scientific research. By offering the biblical account of life’s origin in a form that invites scientific testing, Christians make clear that the study of creation is science. A testable creation model approach to the origin of the universe, the origin of life, the major categories of life, and the origin and spread of humanity allows Christians to make a unique contribution to the question of origins—one that allows for supernatural explanations. By offering testable models capable of making predictions, Christians can positively influence the direction of scientific research in a way that reflects their worldview and in a way that can be respected and embraced by the scientific community. Creation is science.

How did life begin? The answer from textbooks, most learned journals and the media directs our attention to a warm pool in the primitive earth, well-endowed with organic chemicals, from which the first self-replicating living thing spontaneously arose. If you want to see what it might have looked like - go to the Royal Botanic Gardens at Kew, London. Here is how John Lucas describes it (Weekend Telegraph, 1 July 1996):

`In the beginning was the raw material of life: rocks and boiling, bubbling mud, small pools and puffs of subterranean steam ... all were features of an unstable world. They help to set the stark scene of 4,000 million years ago that greets you as you enter Evolution House.'
The main problem for the Kew exhibit, and for all of the propounders of this scenario for the origin of life, is that it lacks any scientific support. It is completely hypothetical - but very few people seem to have noticed!
A modern advocate of this route to chemical evolution is Richard Dawkins. In his view, life is an amazingly lucky accident:

`...We go to a chemist and say...fill your head with formulae, and your flasks with methane and ammonia and hydrogen and carbon dioxide and all the other gases that a primeval nonliving planet can be expected to have; cook them all up together; pass strokes of lightning through your simulated atmospheres, and strokes of inspiration through your brain; bring all your clever chemist's methods to bear, and give us your best chemist's estimate of the probability that a typical planet will spontaneously generate a self-replicating molecule. Or, to put it another way, how long would we have to wait before random chemical events on the planet, random thermal jostling of atoms and molecules, resulted in a self- replicating molecule? ... we'd have to wait a long time by the standards of a human lifetime, but perhaps not all that long by the standards of cosmological time....even if the chemist said that we'd have to wait for a "miracle", have to wait a billion years - far longer than the universe has existed, we can still accept this verdict with equanimity. There are probably more than a billion available planets in the universe. If each of them lasts as long as Earth, that gives us about a billion planet-years to play with. That will do nicely! A miracle is translated into practical politics by a multiplication sum.' (Dawkins, R., The Blind Watchmaker, Penguin: London, 1991, page 145)
Modern theories of abiogenesis are traced back to the Russian biochemist Alexander Oparin who, in 1924, proposed a scheme of chemical evolution. Others picked up the theme: Haldane (1928), Bernal (1947) and Urey (1952). The latter's main contribution was to suggest an initial, hydrogen-rich, reducing atmosphere for the early earth.

Stanley Miller provided experimental data on the synthesis of organic materials which might be collected in a primeval pool. He worked initially (1952) with an atmosphere of methane, ammonia, hydrogen and water vapour (later experiments added other gases, notably carbon dioxide). Electrical discharges produced organic compounds. Numerous research investigations have taken place since Miller began, and in the products of the reaction, ten of the twenty amino acids found in living things have been synthesised naturally. Numerous other compounds were also detected, but these were not deemed so interesting as they do not occur in the proteins of life. It should perhaps be noted that these experiments have produced equal quantities of right-handed and left-handed organic molecules. This is quite different to the amino acids in living systems, where only left-handed molecules occur. The production of left-handed molecules is routine for living systems - but it is a fundamental problem to get them from a primeval soup.

Charles Darwin is often credited with having anticipated the modern chemical evolution scenario, based on ideas he expressed privately in a letter to Joseph Hooker in 1871.

`It is often said that all the conditions for the first production of a living organism are now present, which could ever have been present. But if (and oh! what a big if!) we could conceive in some warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity, &c., present, that a proteine (sic) compound was chemically formed ready to undergo still more complex changes, at the present day such matter would be instantly absorbed, which would not have been the case before living creatures were found.'
Of course, this quotation is only from a private letter. In his public writings, Darwin made reference to the activity of the Creator initiating life. The general view seems to be that Darwin was making a public statement which he was not fully committed to. Thus, Orgel wrote:
`Darwin, bending somewhat to the religious biases of his time, posited in the final paragraph of The Origin of Species that "the Creator" originally breathed life "into a few forms or into one." Then evolution took over: "From so simple a beginning endless forms most beautiful and most wonderful have been, and are being evolved." In private correspondence, however, he suggested life could have arisen through chemistry, "in some warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity, etc. present".'(Orgel L.E., `The Origin of Life on the Earth', Scientific American, October 1994, p.53).
This perception of the situation was shared by Carl Henry:
`But the closing paragraph of The Origin of Species offered a sop to the Christian tradition. There Darwin admits the possibility of a divine origination of the first living cells from whence all else came.'(Henry C.F.H., `Science and Religion', in Henry C.F.H., ed., Contemporary Evangelical Thought: A Survey, Baker: Grand Rapids MI, 1968, p.253)
The reality is that the `warm little pond' scenario should have been abandoned at least 20 years ago! There are three major lines of evidence against it, all of which are well documented in the academic literature:
1. There is no evidence for an early earth with a reducing atmosphere. The consensus now is that the early atmosphere was neutral: composed of carbon dioxide, nitrogen, water and perhaps 1% hydrogen. There is a strong case to be made for the presence of oxygen also. The neutral atmosphere makes the stability of organic molecules a matter of doubt - they would be degraded and lost very quickly.

2. Results from revised Miller-type experiments are quite different. With a neutral atmosphere of water, nitrogen and carbon dioxide, the reaction products are ammonia and nitric acid. Using the most favourable mix of gases, the yield is only about 0.01% amino acid, almost all lysine.

3. Biogenic carbon (derived from living cells) has been detected in the earliest rocks yet discovered in the earth -so there is no record of a time when life was not present! (This is why the date of 4,000 million years was used by John Lucas in his report of the Kew exhibition - there are no rocks known of this age). The origin of life has to be pushed back to where no data is available to constrain models.

Thaxton, Bradley & Olsen have a chapter entitled `The Myth of the Prebiotic Soup' in their book: The Mystery of Life's Origin. This summarises the evidence for the statements given above.

`Based on the foregoing geochemical assessment, we conclude that both in the atmosphere and in the various water basins of the primitive earth, many destructive interactions would have so vastly diminished, if not altogether consumed, essential precursor chemicals, that chemical evolution rates would have been negligible. The soup would have been too dilute for direct polymerization to occur. Even local ponds for concentrating soup ingredients would have met with the same problem. Furthermore, no geological evidence indicates an organic soup, even a small organic pond, ever existed on this planet. It is becoming clear that however life began on earth, the usually conceived notion that life emerged from an oceanic soup of organic chemicals is a most implausible hypothesis. We may therefore with fairness call this scenario "the myth of the prebiotic soup."' (Thaxton, C.B., Bradley, W.L. & Olsen, R.L., The Mystery of Life's Origin: Reassessing Current Theories, Lewis & Stanley: Dallas TX, 1992, p.66).
Why this persistent acceptance of a disproved scenario? The prebiotic soup provides a `creation myth' that is desperately needed by naturalistic scientists. Some have taken the plunge elsewhere and gone extraterrestrial -but few find this convincing either. Can this be science? The best that naturalists can legitimately say is that there is no model of chemical evolution which has survived critical scrutiny and there is no prospect of an imminent solution.
The naturalist rejects intelligent causation - but this explanation is exactly what Christians have come to expect from their reading of the Bible. The creation approach to origins explains why the earth carries evidence of life from its earliest history.

David J. Tyler (1996)