Cyanobacteria are single-celled organisms that played a crucial role in Earth's history.
They caused the first mass extinction and paved the way for complex life by introducing free oxygen molecules into the atmosphere.
Early Earth's Atmosphere
3.5 billion years ago, Earth's atmosphere comprised mostly nitrogen, carbon dioxide, and methane.
Oxygen was primarily bound in molecules like water, not free in the atmosphere.
Oceans were populated by anaerobic microbes, which thrived without oxygen.
Evolution of Photosynthesis
Between 2.5 and 3.5 billion years ago, a species of microbes evolved photosynthesis.
They could convert carbon dioxide and water into oxygen gas and sugars using sunlight.
These microbes were the ancestors of cyanobacteria, named for their blue-green pigments.
Impact of Photosynthesis
Photosynthesis allowed cyanobacteria to produce energy independently, leading to population growth.
Oxygen, a byproduct of this process, began polluting the atmosphere.
Initially, oxygen was absorbed by other chemical reactions, but eventually, cyanobacteria produced more than was absorbed.
The Great Oxygenation Event
Occurred around 2.5 billion years ago, leading to the extinction of many anaerobic life forms.
Known as the Great Oxygenation Event or the Oxygen Catastrophe.
Oxygen reacted with methane, reducing greenhouse effects and causing the Huronian Glaciation, Earth's first major ice age.
Adaptation and Evolution
Life adapted, with aerobic organisms using oxygen for energy.
Oxygen levels fluctuated, eventually stabilizing at approximately 21%.
The availability of oxygen facilitated the diversification and evolution of complex life forms.
Endosymbiosis and Plant Cells
A process called endosymbiosis led to cyanobacteria becoming chloroplasts in plant cells.
This allowed for internal photosynthesis and contributed to the evolution of plant life.
Present Role of Cyanobacteria
Cyanobacteria continue to exist in diverse environments, from oceans to sloth fur.
They are essential for oxygen production and nitrogen fixation, crucial for plant growth.
Conclusion
Cyanobacteria were instrumental in shaping the Earth's biosphere.
They are responsible for the oxygen-rich atmosphere and the development of complex life forms, yet they also nearly eradicated early life due to their impact.