Why do scientists believe that life first emerged from the ocean and onto land well after the ancestors of modern-day cyanobacteria populated the Earth? The cyanobacteria produced radiant energy from the nitrogen and carbon it absorbed from the shallow sea floor. Organisms needed this light energy to see on land.
These bacteria used visible light energy to create chemical energy, expelling oxygen that was converted to ozone. The ozone blocked the Sun's harmful UV radiation from reaching the ground.
The ancient cyanobacteria converted the Sun's radiant energy to heat, warming the ocean waters. They eventually drove many organisms from the oceans and onto land.
These bacteria provided a much needed chemical energy source for organisms living at the shoreline. Without this food source, the first land-dwelling organisms would not have survived.