Though photosynthesis had been developing for more than three billion years, it was less than one billion years ago that a multi-cellular protist organism formed a symbiotic relationship (got infected by) with something called cyanobacteria. This cyanobacteria, also known as blue-green algae, had been happily converting the Earth’s atmosphere to oxygen for 1.4 billion years already, but the multi-cellular protists found that by incorporating a bacteria into their design, they could use the sugars produced during photosynthesis to provide themselves with more energy to develop larger and more complex forms. It is one of the first times in Earth’s history that two separate organisms worked together to create something better. This symbiotic relation continues to this day, and all green plants are a union of cynobacteria and protist.
Algae will save the world! In fact, it already has.