What is the evolutionary significance of "photosynthesis" ?

Question

What is the evolutionary significance of "photosynthesis" ?

Answer 1

In the begining of the history of life on this planet the atmosphere was primarily carbon dioxide, sulphur and other toxic gases.

This meant the atmosphere was unbreathable and very hot.

The first known living things were primitive algae called stromatalites (which still are located in some places in the world such as Shark Bay in Western Australia) these algae lived in shallow seas.

These primitive algae needed little oxygen and to compensate also generated their own oxygen by photosynthesis (using light to convert carbon dioxide and water to sugar and oxygen).

By doing such they soon began producing more oxygen than they needed, thereby began to remove much of the carbon dioxide in the atmosphere and water and replace it with oxygen.

Eventually (billion or so years) the atmosphere became so oxygen rich that larger, more complex photosynthesizers (mostly primitive algae and ferns) could grow. the decreased temperature also allowed organisms to leave the cool water and begin living on land.

As plants began growing more and more on land then the oxygen increased even more rapidly, soon allowing animals to become abundant. Animals need more oxygen than plants because they require more energy to move and get food.

In conclusion: Due the help of primitive ooze generating oxygen for our atmosphere, animals, and eventually humans, can flourish and live peacefully.