| Fluorescence micrographs of cyanobacteria. About 2 billions years ago, cyanobacteria –“ oxygen-producing photosynthetic prokaryotes that used to be called blue-green algae –“ were responsible for launching the process that increased the concentration of atmospheric oxygen from less than 1 percent to about 20 percent today, making possible the evolution of humans and other animals. Credit: Mary Sarcina University College London |
