The Role of Cyanobacteria in Earth's History

Introduction

• Cyanobacteria are single-celled organisms that played a crucial role in Earth's history.
• They were responsible for the first mass extinction and paved the way for complex life by introducing free oxygen into the atmosphere.

Early Earth Atmosphere

• 3.5 billion years ago, the atmosphere was rich in nitrogen, carbon dioxide, and methane.
• Oxygen was primarily bound in molecules like water, not freely available.
• The oceans harbored anaerobic microbes that thrived without oxygen.

Evolution of Photosynthesis

• Between 2.5 and 3.5 billion years ago, a microbial species evolved photosynthesis.
• Photosynthesis allowed these microbes to use sunlight to convert carbon dioxide and water into oxygen and sugars.
• These organisms were the ancestors of cyanobacteria, identified by their blue-green pigments.

Impact of Cyanobacteria

• Photosynthesis gave cyanobacteria an evolutionary advantage, allowing them to proliferate.
• Oxygen, a byproduct, began accumulating in the atmosphere.
• Initially, oxygen was absorbed by chemical reactions, but it eventually built up, leading to atmospheric changes.

The Great Oxygenation Event

• Approximately 2.5 billion years ago, oxygen-rich air caused a mass extinction event (Great Oxygenation Event/Oxygen Catastrophe).
• Oxygen was toxic to existing anaerobic life forms.
• The increase in oxygen reacted with methane, reducing its greenhouse effect and triggering the Huronian Glaciation (first major ice age).

Adaptation and Evolution

• Life adapted to oxygen-rich conditions, with aerobic organisms utilizing oxygen for energy.
• Oxygen levels eventually stabilized around 21%, facilitating the evolution of more complex life forms.

Endosymbiosis and Plant Evolution

• Cyanobacteria were consumed by other microbes in endosymbiosis, evolving into chloroplasts.
• This event was crucial for the development of plant cells capable of photosynthesis.

Current Role of Cyanobacteria

• Cyanobacteria remain widespread in various environments, including oceans, freshwater, soil, and even sloth fur.
• They contribute to Earth's oxygen and nitrogen cycles.
• Cyanobacteria are integral to life's existence on Earth, despite their initial role in almost wiping it out.