Photosynthesis, the process of converting sunlight into energy, dates back to around 3.4 billion years ago. The original method, C3 carbon fixation, involved atmospheric carbon dioxide (CO2) and water vapor (H2O) reacting in the presence of sunlight to produce glucose (C6H12O6) and oxygen (O2). In the early atmosphere, rich in CO2 and poor in O2, C3 photosynthesis thrived, perfectly suited to the conditions.
However, as land plants proliferated around 470 million years ago, they began to significantly reduce atmospheric CO2, making C3 carbon fixation less efficient. While simple, single-celled photosynthetic organisms were largely unaffected, more complex plants in sunnier, hotter, and drier environments faced challenges due to their greater energy needs and the declining CO2 levels.
This decrease in atmospheric CO2 between 470 and 300 million years ago created evolutionary pressure for some plants to evolve more efficient photosynthesis methods. This led to the development of advanced C4 photosynthesis approximately 30 to 20 million years ago. In this process, plants evolved specialized cells within their leaves to more effectively trap and concentrate CO2 and water, enhancing the efficiency of C3 photosynthesis even in lower CO2 conditions.
C4 plants are particularly advantageous in environments prone to droughts, heatwaves, or low CO2 levels. Today, they represent less than 5 percent of plant species but are responsible for almost 25 percent of the fixation of atmospheric CO2. This makes them a crucial component in the biosequestration of CO2, helping to mitigate further warming of our current climate. Their evolution underscores the dynamic adaptability of life on Earth in response to changing environmental conditions.
