For the entire first half of Earth's existence, there was no #oxygen. The world was inhabited only by #microscopic, single-celled #organisms¹.⠀ ⠀ But roughly 2.45 #billion years ago, one such group of simple life forms created oxygen from light, water, and carbon dioxide (yes, #photosynthesis), witnessed the shift of Earth's #biosphere, and ushered in the beautiful possibility of #life as we know it.⠀ ⠀ They're called #cyanobacteria and they caused what is now known as the Great Oxygenation Event, triggering the #evolution of #complex life—from #plants to sponges to worms to fish, and ultimately, #humans. They’ve created and seen the entire history of our world, still living today in ponds, oceans, soil, and even #Antarctic rocks. Sometimes, they become enormous visible colonies in the form of algal blooms, which are both beautiful and deadly. ⠀ ______________⠀ ⠀ ¹ #Microbes have resided on our planet for over 3.7 billion years, spanning approximately 85% of our planet’s #history. By c...