(Institute of Materials, Great Britain, P. 223) The importance is far reaching, from environmental O2 /CO2 balance to the synthesis of artificial herbicides that act on unwanted herbs by blocking some important steps in this energy producing process. The chlorophyll pigment alone has lead to new avenues for thoughts and research on the importance of photosynthetic processes and has paved the way for the synthesis of certain medicinal drugs exploiting its photoprotective mechanisms for preventing light induced damage of cells. The chlorophyll research has added to the significance of this novel energy yielding life process and has led to the foundation of drug therapy for treatment of tumors, carcinoma and related maladies.
In fact the earliest forms of photosynthetic plants principally inhabited the water bodies, especially in the warm mineral rich pools, mainly due to the intense effect of ultraviolet radiation on the land due to the absence of the ozone layer. Instead of oxidizing, with a highly reducing nature of environment, principally due to the sparse oxygen count, the warm pools full of evolving life forms probably utilized the massive energy resource to convert the simple inorganic compounds to complex organic biomolecules, like, purines, pyrimidines, nucleosides, nucleotides, etc, paving the way for the synthesis of nucleic acids and complex proteins and enzymes. (Pearson, P. 10) This definitely potentiated the production of biomolecules required oxygen production. As the oxygen level in the atmosphere increased slowly with the passage of time, plants reached out and slowly colonized the lands progressively transforming their semi-aquatic habitats to terrestrial by nature. With the evolution of the earliest microbes that resembled cyanobacteria, algae and lichens till the further differentiated poikilohydric bryophytes evolved. About 25 million years ago, these non vascular bryophytes were soon followed with vascular homioihydric plants capable of maintaining their internal water content at an optimum level irrespective of the external environmental conditions. However before the origin of these photosynthesizing life forms the challengingly low levels of atmospheric oxygen as hypothesized by the geologists, required an explanation of unknown factors that increased the atmospheric oxygen count at a considerable extent. This unknown process of oxygen accumulation in the atmosphere through an unexplained time gap of hundred million years can be associated with a number of presumable theories each of which has its own investigational platform.
"The red line shows the inferred level of atmospheric oxygen bounded by the constraints imposed by the proxy record of atmospheric oxygen variation over Earth’s history. The signature of mass-independent sulphur-isotope behaviour sets an upper limit for oxygen levels before 2.45 billion years ago and a lower limit after that time. The record of oxidative weathering after 2.45 billion years ago sets a lower limit for oxygen levels at 1% of PAL, whereas an upper limit of 40% of PAL is inferred from the evidence for anoxic oceans during the Proterozoic. The tighter bounds on atmospheric oxygen from 420 million years ago to the present is set by the fairly continuous