What Happened When Photosynthesis Evolved?

While we take it for granted today, chlorophyll and photosynthesis radically altered the environment.

Photosynthesis is the method by which plants convert carbon dioxide and water into sugars via the input of light and release free oxygen as a byproduct. Algae, plants and some bacteria use photosynthesis. It is not precisely certain when photosynthesis arose, but the best estimates are that the first photosynthetic organisms date back to between 3.8 to 3.4 billion years ago.

Early Equilibrium

From 3.4 to 2.4 billion years ago, most photosynthetic creatures on the planet were blue-green algae and cyanobacteria. The oxygen released by photosynthesis was re-absorbed by minerals in the earth's crust, or absorbed by dissolved compounds in the ocean.

Chloroplasts and the Great Oxidation Event

Plant cells use chlorophyll in specialized cells called chloroplasts; sometime between 2.5 and 2.4 billion years ago, chloroplasts evolved, and the amount of excess oxygen released by photosynthesis started to exceed what could absorbed by mineral beds in the ocean sediments. This caused a massive extinction.

Rising Oxygen Levels and Glaciation

Rising oxygen levels combined with atmospheric methane, which oxidized to carbon dioxide. Methane is a much more powerful greenhouse gas than carbon dioxide, and this triggered a nearly half-billion year glaciation event on the planet.

References

• National Institute of Health: When Did Oxygenic Photosynthesis Evolve?
• Scientific American: Breathing Easy Thanks to the Great Oxidation Event:
• Science Daily: Oxygen May Be Cause of First Snowball Earth