Joseph (2009) begins his controversial article by suggesting that abiogenesis is speculative and lacks scientific support. Is this position correct? Let us consider the scientific evidence, beginning with the works of Friedrich Wöhler, who demonstrated that urea could be formed “without the need of an animal kidney” and the findings of Joseph Proust in 1807, the first chemist to note that hydrogen cyanide could form complex polymers and several organic compounds (Miller and Lazcano, 2002).

After a series of pioneer explorations, the key experiment of Stanley Miller in the fifties, marked the origin of the prebiotic chemistry field using the demonstration that a reductive atmosphere over a water pond could generate amino acids, among other compounds (Miller, 1953). After this experiment and attempts to replicate the original composition of Archean atmosphere on Earth, laboratory simulations have led to the demonstration that many molecules of biochemical interest could be synthesized on water ponds under reducing, mildly reducing and even neutral atmospheric conditions. Also, the hydrothermal systems (in particular the deep sea hydrothermal vents) could provide the appropriate setting for the abiotic formation and accumulation of organics, providing precursors for the chemical evolution (i.e. Ferris, 1992; Simoneit 1995).

The hydrothermal and volcanic environments also favor conditions conducive to the abiogenic development of life due to the availability of sulphide and inorganic pyrophosphate, two reactants that are likely of importance to the final development of the first metabolism.

Joseph (2009) is correct in his assertion that we do not have a definite model for the life emergence from a complex organic system, but this issue is no longer subject of vague speculations and religious approaches.

Modern molecular phylogenies have led to the acceptance of the idea that all living beings are descendants from a single ancestral form life (the “LUCA”, last universal common ancestor; de Duve, 2008). The fundamental questions are: i) how the products of abiotic synthesis of organics increase their complexity and organization grade to give the LUCA? And ii) if only one original life form generates the evolutionary tree that lead to the modern biological diversity, is it possible that single molecules and chemical structures evolve following similar evolutionary rules (a question that originates the chemical evolution field of study)?

The RNA world hypothesis is just one of the possible approaches. Joseph (2009) obviates again the exploration of alternative approaches to the RNA world hypothesis and the determinism induced by the chemistry laws. In this sense, one of the earlier criticisms to the abiogenic origin of life is the Fred Hoyle´s “junkyard tornado” argument: A junkyard contains all the bits and pieces of a Boeing-747, dismembered and in disarray. A whirlwind happens to blow through the yard. What is the chance that after its passage a fully assembled 747, ready to fly, will be found standing there? (Hoyle, 1983). Although logical, Hoyle's argument ignores the rules of chemistry and the paths on the development of complexity. Joseph echoes Hoyle by stating “The likelihood that life on Earth began in an organic soup is the equivalent of discovering a computer on Mars and claiming it was randomly assembled in the methane sea." Again, "complexity" may be the answer to Joseph's criticism.

An analysis of prebiotic chemistry has shown us that a limited number of bulk material of biochemicals could be synthesized in a variety of conditions: amino acids, nucleobases and a set of carboxylic and hydroxycarboxylic acids. To employ mathematical probability to refute this possibility is not appropriate as the laws of chemistry leads only to a limited number of structures, and this fact constraint the subsequent evolution.

Modern approaches (i.e. all the Günter Wächtershäuser papers) shows that a chemoautotrophic origin of life through a protometabolic, out of equilibrium, chemical system capable of carbon fixation, with the aid of surface of minerals and transition metal catalysts, could be a plausible alternative model for the “replication-first” models based on the autocatalytic polymerization of monomers and aggregation and replication of polymers (as RNA World).

A number of scientists are engaged in the study of origin of Krebs cycle or plausible variants, as reverse-Krebs cycle, and this has direct implications regarding the origin of life. This is due to two interesting facts: some hydroxycarboxylic acids implicated in the central metabolism are easily synthesized in abiotic conditions (Ruiz-Bermejo et al., 2007) and a chemical cycle could decrease the entropy and increase the complexity of a system, an interesting field that has their pioneer work in the Belousov-Zhabotinsky reaction.

Is not the aim of a short comment to discuss extensively about the prebiotic chemistry and the possibilities of chemical evolution from single, inorganic materials in a planetary environment. The problem is that Joseph (2009) obviates all these findings which could explain the origin of life on Earth, and instead suggests that prebiotic chemistry is a matter related with Christian doctrine and ignoring that the laws of chemistry do not follow the mathematical probability.

Admittedly, if the early Earth did not generate life per se, then this life must have come from elsewhere. Nevertheless, the detailed revision of the possibilities of Panspermia performed by Dr. Joseph contains some flaws that we should consider. First, the controvery about microbial fossils in carbonaceous chondrites. Care must be taken with this issue as modern works shows that is nearly impossible to distinguish nonbiogenic bacteriomorphs (coating artifacts, microstructures of mineral and polymeric nature, mineral grains) and actual microfossils based only in microscopy images. The study of possible microfossils in chondrites is based largely on the works of Richard Hoover. These microfossils shows resemblance with bacteriomorphs found in ancient rocks on Earth, for example those of Warrawoona group in Australia and it was proposed that these putative fossils are actually microstructures formed after hydrothermal alteration that mimics bacterial structures (Binet et al. 2005).

It is not my intention to deny the possible existence of ancient biological material in meteorites, but the numerous references to abiotic biomorphs in nature, together with the lack of biomarkers (including the possibility of physically induced enantiomeric excess in amino acids) suggest that the findings in chondrites are not unambiguous. In the same line, Dr. Joseph states that “these organics (referring to nucleobases as adenine, guanine, uracil and related compounds as melamine, all found in carbonaceous chondrites) were most likely produced biologically”. Again, Dr. Joseph downplays the chemical literature which has demonstrated the abiotic synthesis of nucleobases and melamine in cold prebiotic environments (Menor-Salvan et al. 2009) and the synthesis of pyrimidine ribonucleotides without sugar is possible in prebiotic conditions (Powner et al. 2009). This could be extended to all the organic compounds found in carbonaceous chondrites: all have its prebiotically plausible synthesis demonstrated and, hence, should not be considered unambiguous biomarkers.

As conclusion, we could say that there are too many questions unsolved in the study of origin of life. However, if we accept that Joseph's (2009) statements are correct and “life is not created from non-life” and even if the bacteria were delivered by meteorites, the questions are: i) how and where this original life was formed?; ii) why was it impossible for life to have formed on the early Earth?; iii) What were the conditions on those planets which provided these life "seeds" and how did these conditions make life possible? And iii) if life is an heredity from planet to planet since the very first origin of Universe, as suggest Dr. Joseph, we could revive the old philosopher question: How was the first life formed? Could be the consequence of the aristotellic Το Θείον or first metaphysical and aeternal substance that is responsible of the organization of living beings?

As an alternative to the conclusion of Joseph (2009) I believe the evidence demonstrates that the origin of life in situ on Earth and other planets with the appropriate conditions is a plausible and non-speculative possibility.

REFERENCES

Binet, L., Gourier, D., Skrzypczak, A., Derenne, S., Robert, F., 2005. Insoluble organic matter in carbonaceous chondrites and Archean cherts. In „Astrobiology: Future Perspectives“. Ehrenfreund P. (Ed.) Springer Netherlands.

De Duve, C., 2008. Chemistry and selection. In “Origin of Life: Chemical approach”. P. Herdewijn and M. V. Kisakürek (Eds.). Werlag Helvetica Chimica Acta. Zurich.

Ferris, J.P., 1992. Chemical markers of prebiotic chemistry in hydrothermal systems. In “Marine Hydrothermal Systems and the Origin of Life”. N. G. Holm (ed.) Kluwer Academic, Dordrecht.

Hoyle, F., 1983. The Intelligent universe. Michael Joseph Ltd. London.

Joseph, R. 2009. Life on Earth came from other planets. Journal of Cosmology, 1, 1-56.

Menor-Salvan C., Ruiz-Bermejo, M., Guzman M. I., Osuna-Esteban, S., Veintemillas S., 2009. Synthesis of pyrimidines and triazines in ice: Implications for the prebiotic chemistry of nucleobases. Chemistry: A European Journal, 15, 4411-4418.

Miller, S.L., 1953. Production of amino acids under possible primitive Earth conditions. Science, 117, 528.

Miller, S.L., Lazcano, A., 2002. Formation of building blocks of life, in Life´s Origin: The beginnings of Biological Evolution. Schopf J.W. (ed.) Califormia University Press, Berkeley.

Powner, M.W., Gerland, B., Sutherland J.D., 2009. Synthesis of activated pyrimidine ribonucleotides in prebiotically plausible conditions. Nature 459, 239-242.

Ruiz-Bermejo, M., Menor-Salvan, C., Osuna-Esteban S., Veintemillas-Verdaguer S., 2007. Prebiotic microreactors: A síntesis of purines and dihydroxy compounds in aqueous aerosol. Origin of Life and Evolution of Biospheres, 37, 123-142.

Simoneit, B.R.T., 1995. Evidence for organic synthesis in high temperature aqueous media-facts and prognosis. Origin of Life and Evolution of Biospheres, 25,119-140.