Without it, carbon-based life as we know it on Earth could not exist.

Photosynthesis - the biological ability of converting light into energy - is ultimately what keeps all of us alive. Even when  petroleum (literally, "rock oil") is burned in the form of gasoline, it's just the release of sunlight energy gathered by plants billions of years ago. In a very real way, it is the reason you and I are able to live and breathe. The question that scientists have been wondering about is - just when and where did this process begin?

Earlier, scientists believed that cyanobacteria was descended from earlier phototrophic bacteria.  This latest research indicates that it was the opposite. The fact that so many of these genes are unique to cyanobacteria indicates that they originated with this lineage.

Additional evidence includes 3.4-billion-year-old fossils that show the oldest photosynthetic organisms as being filamentous (that is, having long, tube-like extensions). This supports the argument that pro-cyanobacteria were the first phototropic life forms.

Pro-cyanobacteria were thus the ancestor of "light-eating" plants able to store unlimited sunlight as energy. This in turn enabled the rise of the diverse biome that exists on Earth today. "This invention gave an enormous evolutionary advantage to cyanobacteria, so that they dominate in the vast majority of photosynthetic communities," Mulkidjanian says.

Not all of the scientific community agrees with Mulkidjanian, however. "I did not see any evidence that would convince me that this group of organisms shouldn't instead be called pro-phototrophs rather than pro-cyanobacteria," says Robert Blankenship of Washington University in St Louis, Missouri. According to Blankenship, cyanobacteria's more complex photosynthetic apparatus compared with that of other bacteria suggests that they evolved more recently.