Question

Why was the evolution of cyanobacteria of such importance to the further evolution of life on Earth? What component of the geological record is used to date the evolution of cyanobacteria? (Section 12.2)

Short answer

Cyanobacteria produced oxygen, leading to the Great Oxygenation Event and enabling the evolution of complex life. Stromatolites are used to date their evolution.

Step-by-step solution

- Understanding Cyanobacteria's Role

Realize that cyanobacteria were among the first organisms to perform photosynthesis. They played a crucial role in producing oxygen through this process.

- Impact on Atmosphere

Describe how the photosynthesis performed by cyanobacteria produced oxygen, which accumulated in the Earth’s atmosphere. This accumulation of oxygen led to the Great Oxygenation Event.

- Importance for Evolution

Explain that the rise in atmospheric oxygen allowed for the evolution of aerobic (oxygen-using) organisms. This was crucial for the development of complex life forms.

- Geological Record Component

Identify the geological evidence used to date the evolution of cyanobacteria. This component is primarily stromatolites, layered sedimentary formations created by the growth of cyanobacteria.

Key concepts

Photosynthesis

Photosynthesis is a process used by plants, algae, and certain bacteria to convert light energy into chemical energy stored in glucose. Cyanobacteria were among the first organisms to perform photosynthesis. They use sunlight to split water molecules, releasing oxygen as a byproduct. This was a groundbreaking development because cyanobacteria produced significant amounts of oxygen. This oxygen gradually accumulated in the atmosphere, paving the way for the evolution of more complex life forms.

Photosynthesis played a pivotal role in shaping the planet's environment and biological makeup. Without it, the oxygen levels we depend on for life would not have developed.

Great Oxygenation Event

The Great Oxygenation Event (GOE) occurred around 2.4 billion years ago. This was a critical turning point in Earth's history, marking the first time that the atmosphere had substantial amounts of oxygen. Cyanobacteria were the principal drivers of the GOE. Through photosynthesis, they released oxygen into the oceans, which eventually saturated and began to escape into the atmosphere.

This event transformed the Earth from an anaerobic to an aerobic environment. The increased oxygen levels triggered the formation of the ozone layer, which protects life from harmful UV radiation. The GOE is evidenced in geological records by the appearance of banded iron formations, showing the transition from reduced to oxidized iron as oxygen entered the oceans and atmosphere.

Aerobic Organisms

Aerobic organisms are those that need oxygen to survive. The rise in atmospheric oxygen due to the photosynthetic activities of cyanobacteria allowed these organisms to evolve. Oxygen is more efficient for energy production compared to anaerobic methods, which leads to the development of more complex and multicellular life forms.

Aerobic respiration enables cells to produce far more energy from glucose than anaerobic respiration. This extra energy supported the development of diverse and complex organisms, eventually leading to the explosion of life forms in what is known as the Cambrian Explosion around 541 million years ago. This event saw the rapid diversification of life, with many modern animal phyla emerging.

Stromatolites

Stromatolites are layered sedimentary formations created by the growth of cyanobacteria. They are among the oldest evidence of life on Earth, dating back to some 3.5 billion years ago. Cyanobacteria grow in colonies, and as they trap and bind sediment, they create these layered structures.

Stromatolites offer crucial insights into early life and the environment on ancient Earth. Their presence acts as a geological marker to date the evolution of cyanobacteria, linking their development to significant events like the Great Oxygenation Event. By studying stromatolites, scientists can trace back the origins and impacts of cyanobacteria on the planet.