Dr. Joseph in an interesting, speculative article, details an elaborate theory explaining how life may have been transported to Earth (Joseph 2009). However, whereas many of his ideas are intriguing and closely follow the facts, a close scrutiny reveals that he also draws questionable conclusions about the viability of the theory of abiogenesis. Joseph points out that the origins of life are unknown, but then he asserts that the possibility life began in an organic soup is as farfetched as a self assembled computer being found on Mars; and this conclusion is debatable.

His central contention is that life was brought to earth via comets or asteroids, a view propounded by, amongst others Chandra Wickramasinghe and Sir Fred Hoyle (Hoyle & Wickramasinghe 1993, 2000). He argues that microbes could be cold stored as spores and could be brought back to life millions of years hence. All this is within the realm of possibility, and it is true microbes can remain dormant as spores for millions of years (Vreeland et al. 2000). But in the absence of unambiguous proof his argument that spores from space are the source of life on Earth, cannot be treated as confirmed fact. Undoubtedly, as he notes debris produced by supernovae could have bombarded the Earth, as demonstrated by the presence of iron and Carbon 12 in ancient rocks that are over four billion years old. But from here to conclude that what was brought down to earth included living organisms is extremely speculative.

For example let us take the case of the ALH 84001 meteorite believed to have been ejected from Mars (McKay et al. 1996). In 1996 this meteorite rose from obscurity and became the most talked about rock in the history of science because of claims that it had distinct traces of fossilized micro life (McKay et al., 1996). This claim has been contested due to indications of contamination and because similar shapes have been found on terrestrial samples as well (Anders 1996, Bell 1996, Becker et al 1997; Bradley et al. 1997; Shearer and Papike, 1996). Similar arguments can be put forward in the case of the other carbonaceous chondrites. To merely assert that, “… thus they are likely biological in origin” should really read “thus they could be of biological origin – or perhaps not."

On the other hand, the wide spread belief that the first organisms were entirely cooked up in within an organic soup is also speculative and Dr. Joseph’s quote of Francis Crick (1981) is well taken in this context.

A number of scientists have argued that the key ingredients for the creation of life on Earth originated in space, mixing with chemical composition of this planet and then becoming energized, organized, and alive (Menor-Salvan et al. 2009; Pizzarello 2007; Powner et al. 2009; Sidharth 2002, 2006). This dual origin for the development of life rests upon the belief that key ingredients like amino acids, but not yet fully formed life had reached the Earth from outer space and chemically interacted with other ingredients present on the Earth, to form life ( Johnson et al. 2008; Lascano and Bada, 2004; Menor-Salvan et al. 2009; Pizzarello 2007; Powner et al. 2009).

For example, numerous studies have identified the existence of complex molecules in interstellar space, including the cool dust clouds of the Orion Nebula and in the constellation of Sagittarius (Belloche 2009). A number of independent scientists have confirmed the presence of methyl cyanide, water vapour, formaldehyde, methyl alcohol and even the potable ethyl alcohol (Zelic 2002).

Joseph (2009) argues that these complex molecules are not the abiotic, or prebiotic, but may be the actual fingerprints, the residue of living organisms. Although this is within the realm of possibility, it is just as likely that since these molecules are related to life, they may have become combined to generate life.

Over one hundred and twenty molecules including those which chemists designate as Methanol and Ethanol, from diatomic molecules through those containing thirteen atoms have been detected in the dark interstellar clouds which are opaque to light (Belloche 2009; Fraser 2002).. These appear to be nothing less than factories for building complex molecules. The mechanism could be that some of the simpler molecules are frozen in ice droplets which are bombarded by ultra violet radiation from very near by young stars, cosmic rays and ions, all these inducing the formation of very complex molecules by the process of breaking up of molecules and recombination. These speculations have been confirmed by laboratory simulations (Williams 2007).

The polycyclic aromatic hydrocarbons (of aerosol spray and global warming notoriety) under interstellar conditions convert to complex molecules, like alcohols, ethers and quinons (Jura 2005). These are ubiquitous in living organisms today, helping in various energy transfer processes like photosynthesis and the ability to absorb ultra violet radiation which is harmful to, for example amino acids. The universe exhibit traces of polycyclic aromatic hydrocarbons. These are the most abundant class of carbons in the universe, which suggests the ingredients for creating life are also widespread. Although supportive of Joseph's thesis that life may exist on innumerable planets, and some of these life forms may have fallen to Earth, these findings also support theories of abiogenesis. If life formed on some other planet in an organic soup, then why could not life arise from an organic soup on Earth?

This apart the space crafts Giotto and Vega which flew by Comet Halley glimpsed carbon rich molecules while space based observations revealed the presence of Ethane and Methane in Comets Hyakutake and Hale Bopp (Cottin 2001). Space dust reveals organic carbon. Interestingly some thirty tons of such carbon is brought down to the earth each day by the interstellar dust. Meteorites have shown nucleo basis, ketones, quinines, carboxylic acids, amines and amides (Folsome et al. 1973; Hayatsu et al. 1975; Stoks and Schwartz, 1979, Van der Velden and Schwartz, 1977). In fact as many as eight of the twenty amino acids involved in life processes have been identified besides some sixty others. This August, NASA announced that an analysis of data from its Stardust mission revealed, for the first time the presence of the amino acid glycine in an icy comet.

Comets which inhabit the cool and dark regions of the solar system definitely contain the building blocks of life (Hoyle and Wickramasinghe 1993, 2000). But again, it would be a giant leap of logic, if we follow Dr. Joseph and say that they contain living organisms, though certainly this cannot be ruled out. There is increasing evidence through spectroscopic, space craft and even laboratory examinations of debris which fallen to Earth, which show that the frozen dirty ice balls known as comets, contain not just molecular compounds of carbon, hydrogen, nitrogen and oxygen, but also even more complicated sugar related substances. Studies at NASA’s Ames Research Centre indicate the presence of polyhydroxilated compounds as well (Cooper 2001). Studies at the Russian Academy of Sciences have confirmed the possibility of abiogenous synthesis of complex organic compounds (monomeric units of nucleic acids) on the surface of comets, asteroids, meteorites and space dust particles in outer space (Kuzicheva 2007).

Joseph (2009) proposes life came to Earth from other planets. The question remains, how did life begin? If we accept life may have begun through abiogenic mechanisms on another planet, then the same processes may have occurred on this world, possibly via the combination of materials delivered from space with those already present on Earth. The presence of sugar related compounds and other complex molecules in meteoritic and cometary objects support the abiogenic theory of dual origins. Some of these molecules, possibly proteins or amino acids—but not yet living organisms—are very likely to have been transported to Earth, and further biochemical reactions would have taken place thereby giving life to non-life. Such a hybrid view for the origin of life is consistent with observations and experiments.

Consider again, amino acids. The amino acids produced in the laboratory like the Urey-Miller type experiments show equal quantities of the left handed and right handed varieties, which is reasonable (Brooks 1985). However in life processes, the left handed molecules predominate over the right handed molecules. Interestingly in the amino acids found on meteorites (Cooper et al. 2001; Cronin et al. 1993), we have exactly this preponderance of left handed amino acid molecules! Joseph (2009) would argue this disproves the Miller experiments and favors the theory of panspermia. However, what it shows is that the ingredients for life could have been delivered to our planet from space.

How can extra terrestrial molecules trigger off chemical reactions leading to the origin of life? Firstly complex molecules containing six or more carbon atoms are known to produce amino acids in warm acidic water; as many as fifteen carbon bonds have been created. These molecules form droplet-like capsules. Indeed such capsules, the precursors of cell walls were also exhibited by extracts from meteorites—when organic compounds from these meteorites were mixed with water, they assembled into cell membrane like structures with complex organic compounds. Actually what happens is that these molecules are amphidilic: One of their ends has a preference for water, while the other behaves in an exactly opposite manner. The ends which prefer water form the outer circles of the cell like structures while at the same time hiding within are the inner ends. Such structures could also house other interstellar components, for example quinons which could harness light and other forms of energy required for life processes.

It appears that amino acids, quinons, amphibilic molecules and the like were transported to the Earth by meteoritic dust or cometary fragments. These could well have kick started the first life processes on our planet.

Breslow and Cheng (2009) found that the predominant left handed amino acids characteristic of life could indeed have been delivered by meteorites, thus seeding the Earth with the ingredients for life. This new evidence was found on the surfaces of meteorites which had crashed into the earth in relatively recent times. Dr. Breslow exposed amino acid chemical precursors to the amino acids found on the meteorites and discovered that these cosmic molecules could transfer their left handedness to the simple amino acids characteristic of life. This would explain why there is an excess of left handed amino acids in living creatures.

An important component of early genetic material found in the Murchison meteorite is extraterrestrial in origin (Cooper et al. 2001; Cronin et al. 1993), indicating that life’s raw materials came from sources beyond the Earth. These include uracil and xanthine, which are precursors to the molecules that make up DNA and RNA, and are known as nucleobases. Further analysis demonstrated that these nucleobases contain a heavy form of carbon which could only have been formed in space—those formed on Earth consist of a lighter variety of carbon (Martins et.al 2008).

Joseph (2009) argues that these key DNA ingredients are evidence for extra-terrestrial life. Further, he suggests the DNA of living organisms may have been shattered by cosmic rays, and this explains the presence of these DNA-related substances. Although this is not beyond the realm of possibility, Dr. Zita Martins (Martins et.al 2008), concludes otherwise:

“We believe early life may have adopted nucleobases from meteoritic fragments…. which enabled them to pass on their successful features to subsequent generations" (Martins et. al 2008).

Between 3.8 to 4.5 billion years ago large numbers of rocks similar to the Murchison crashed down to Earth at the time when primitive life was forming. The heavy bombardment delivered large amounts of meteorite material to the surface on planets like Earth and Mars. Joseph (2009) argues that this material represents the fragments of a planetary system which orbited a "parent star." Further, he speculates that this debris harbored life. As speculation and theory, the idea is intriguing. However, the evidence for microfossils is not conclusive, whereas a number of independent investigators have identified material which is associated with life. This raises the possibility that abiogenesis may occur on many planets including the Earth.

As summed up by Professor Mark Sephton: “Because meteorites represent left over materials from the formation of the solar system components for life—including nucleobases—could be widespread in the cosmos.”

According to Professor Akiva Bar-Nun and coworkers (Bar-Nun et.al. 2009) the essential ingredients for life to form in the Earth’s ancient environment were available in and delivered by comets. "When comets slammed into the Earth through the atmosphere about four billion years ago, they delivered a payload of organic materials to the young Earth, adding materials that combined with Earth's own large reservoir of organics and led to the emergence of life."

It must be mentioned that the method of transfer to the Earth of these complex molecules is consistent with the evidence cited by Dr. Joseph. However, it is difficult to agree with Dr. Joseph’s primary premise that only life can produce life, apart from the fact that we do not even have a satisfactory definition of life itself. If the universe has a finite age, as is now universally believed, then life must have also had an origin. Therefore, if life on Earth came from other planets, Joseph (2009) must also explain how life was first formed on those planets.

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