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The author of the article " When Did Photosynthesis Emerge on Earth?” is David J. Des Marais. The author examines the period when photosynthesis emerged and the issues surrounding its emergence in our biosphere. The author looks at the historical and evolutionary evidence to advance the topic of the emergence of photosynthesis. The article is majorly based on the biosphere changes and the changes in the oxygen levels and the metamorphosis of sedimentary rocks to illustrate the sequence of biochemical records and trends. In the early Earth’s history photosynthesis has highly evolved. Also through the rapidity of its emergence has suggested that there was no existence of flukes and it could also on other worlds also (Des Marais, 2000).
The question on when did photosynthesis take its place in the place Earth is an issue which has been researched widely in order to unearth the many unknown mysteries. Probably life is thought to have begun early the history of the Earth, perhaps more than 3800 years ago and through the years it has received a lot of sophistication in terms of metabolism. Great developments of biomolecules and key pathways reveal a great deal of evolutional innovations in the field of photosynthesis. A sequence of genes’ information has been used in the analysis of the major photosynthetic bacteria. Also the molecular origins of the major photosynthetic bacteria has been clarified to a great extent (Des Marais, 2000).
There is a vast base of evidence defending the oxygen photosynthesis, from the molecular oxygen which is released by photosynthesis. Before the emergence oxygenic photosynthesis, ambient oxygen levels were notably low, this resulted from the chemical sinks from rock weathered and reduced geothermal outflows which greatly exceeded the abiotic sources of oxygen. Another supporting evidence which is recorded by the author is the dissociation of water which is coupled by of the atom of hydrogen to space. Also the discovery of the sterane biomarkers below in the sediments of about 2700 Ma has not only demonstrated existence of organisms which depend on oxygen for respiration but also the availability of free oxygen for the process of sterol biosynthesis. Extremely low temperatures also has been attributed to the existence of methanotrophic bacteria, which have found to require both methane and oxygen. Indeed, the many sedimentary deposits of reduced sulfide, organic carbon, sulfate and ferric iron along the coastal margins and on the continental platforms are some of the prominent legacies of the time of the oxygenic photosynthetic activity (Des Marais, 2000).
Overwhelming and undisputable evidence has indicated that eukaryotic photosynthesis records it origin from endosymbiosis of the cyanobacterial-like organisms, at the later times they became chloroplasts (Margulis, 1992). So it the photosynthesis’ evolutionary origin highly lies in the bacterial domain. The current distribution of photosynthesis in the family of bacteria which has resulted from the horizontal gene transfer is very evident, this has led to shuffling of the information which records the various parts of photosynthetic apparatus, by this it hard to trace one simple diagram that can represent accurately the evolution of photosynthesis (Raymond et al., 2002). However, all is not lost as some patterns can be discerned more carefully through a detailed analysis of these parts and some helpful conclusions drawn. Additionally, the explosive growth of the genomic data recently on all kinds of photosynthetic organisms promises a great deal in the unravelling of this complicated evolutionary process.

The author goes ahead to indicate that, when photosynthesis was developed by our biosphere, there was a consequential development of a large magnitude of energy resource from the process of oxidation- reduction which were associated with hydrothermal and weathering activity. The biological clock of the earth gives a sharp contrasts between the biosphere and the young plants and animals. It is indicated by the dual molecular and geological microorganism record, that the early biosphere was highly complex. Lastly, it is noted that the biosphere went through a stage in which its photosynthetic populations exclusively depended on abiotic sources.
According to Des Marais (2000), little is known concerning the about the origins of photosynthesis but numerous suggestions have tried to explain its origin though without much evidence to support the suggestions. There is a lot of suggestive evidence of the presence of photosynthetic organisms approximately 3.5 billion years ago, that is the form of stromatolites, which are layered structures resembling the forms which are produced by some cyanobacteria and numerous microfossils which can be interpreted to arise from phototrophs. Also there is isotropic evidence for the autotrophic carbon fixation approximately at 3.8 billion years ago, this can be used to link these organisms to photosynthesis.
In conclusion, it is worth noting that photosynthesis so far is the only significant process of storing solar energy on Earth and also is the source of the food consumed and most of the world’s energy resources. Therefore, an understanding of its origin and its evolution is of substantial interest, since it will highly help in explaining the inefficiencies in the process and come up with ways which can be used in trying to improve a number of aspects for energy and agricultural applications. Lastly, the evidence which is accumulated points photosynthesis to early Earth’s history, but was not the earliest metabolisms. The earliest form of photosynthesis was anoxygenic with the oxygenic form coming up later.

References
Blankenship, R. E. (2013). Molecular mechanisms of photosynthesis. John Wiley & Sons.
Des Marais, D. J. (2000). When did photosynthesis emerge on Earth?. Science (Washington), 289(5485), 1703-1705.
Margulis, L. (1993). Symbiosis in cell evolution: microbial communities in the Archean and Proterozoic eons.
Olson, J. M., & Blankenship, R. E. (2004). Thinking about the evolution of photosynthesis. Photosynthesis Research, 80(1-3), 373-386. Raymond, J., & Blankenship, R. E. (2008). The origin of the oxygen-evolving complex. Coordination chemistry reviews, 252(3), 377-383.