Although during the Precambrian time, 4 billion years ago, Paleozoic, Mesozoic, and Cenozoic eras there were no toothbrushes or toothpastes, teeth themselves first had to evolve. The first organisms were single celled and got their energy by staying warm by earth’s core and eating chemicals. Some of these cells drifted to the surface and used the abundant carbon dioxide in the atmosphere to photosynthesise. The waste product of this process was a highly reactive element, oxygen. The Earth’s atmosphere suddenly contained high levels of oxygen that killed off many organisms leaving only a few cells. These cells that survived learned to cope with the oxygen rich atmosphere. The main reason these cells survived is because of symbiosis. The cells
