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• Evolutionary Essentials
 Photosynthesis
The first forms of life on Earth were single-celled organisms called prokaryotes. Like every living thing, these cells burned fuel (food) for energy. Some prokaryotes developed a way to turn the sun’s energy into sugar, the fuel they needed to live. This process is called photosynthesis.
During photosynthesis, oxygen is released as a waste product. Over two billion years, photosynthetic bacteria releasing waste oxygen into the oceans and atmosphere transformed the world. As oxygen saturated the oceans, it escaped into the atmosphere—creating the air we breathe today.
 Over time, oxygen paved the way for new life.
By forming the ozone layer, which blocks the sun’s harmful radiation, oxygen created a protective environment. Here, new life forms that flourished in the presence of oxygen could evolve.
Without the development of photosynthetic organisms during the Precambrian, life as we know it would not exist.
Continue to Sexual Reproduction & Natural Selection. >>
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