There’s an organism that significantly altered the world, causing the first mass extinction in Earth’s history and paving the way for complex life. This organism is cyanobacteria, a simple, single-celled life form without nuclei or any other organelles. The story of cyanobacteria is a pivotal chapter in the story of life on Earth.
Earth’s atmosphere wasn’t always the oxygen-rich mixture we breathe today. Around 3.5 billion years ago, the atmosphere was mostly nitrogen, carbon dioxide, and methane, with almost all oxygen locked up in molecules like water. The oceans were populated by anaerobic microbes, simple, unicellular life forms that thrive without oxygen. However, between 2.5 and 3.5 billion years ago, one of these microbial species, probably floating on the ocean’s surface, evolved a new ability: photosynthesis. These organisms, the ancestors of what we now call cyanobacteria, could harness the energy from sunlight to turn carbon dioxide and water into oxygen gas and sugars, which they used for energy.
Photosynthesis gave these ancient bacteria a significant advantage over other species. They could produce their own energy from an almost endless supply of raw ingredients, leading to a population explosion and the release of a new waste product: oxygen. Initially, the extra oxygen was absorbed by chemical reactions with iron or decomposing cells. However, after a few hundred million years, the cyanobacteria were producing oxygen faster than it could be absorbed, leading to a buildup of the gas in the atmosphere. This was toxic to the rest of Earth’s inhabitants, resulting in a mass extinction about 2.5 billion years ago, known as the Great Oxygenation Event or the Oxygen Catastrophe.
The oxygenation of the atmosphere also led to Earth’s first, and possibly longest, ice age, the Huronian Glaciation. Methane, a potent greenhouse gas that had been keeping the Earth warm, reacted with the extra oxygen to form carbon dioxide and water, which don’t trap as much heat. This caused the planet to become a giant snowball for several hundred million years. Eventually, life adjusted. Aerobic organisms, which can use oxygen for energy, started absorbing some of the excess gas in the atmosphere. The oxygen concentration fluctuated until it reached the approximate 21% we have today. This allowed organisms to use the chemical energy in oxygen, leading to the diversification and evolution of more complex forms.
Cyanobacteria played a crucial role in this story. Hundreds of millions of years ago, another prehistoric microbe swallowed a cyanobacterium whole in a process called endosymbiosis. This microbe acquired its own internal photosynthesis factory, becoming the ancestor of plant cells. Cyanobacteria evolved into chloroplasts, the organelles that carry out photosynthesis today.
Cyanobacteria are still present in almost every environment on Earth: oceans, fresh water, soil, Antarctic rocks, even sloth fur. They continue to pump oxygen into the atmosphere and pull nitrogen out to fertilize the plants they helped create. Without them, life on Earth as we know it would not exist. However, thanks to them, we almost didn’t have life on Earth at all.
Research and create a timeline that highlights the major events in the history of cyanobacteria, from their emergence to their role in the Great Oxygenation Event and beyond. Include illustrations and brief descriptions for each event. This will help you understand the chronological impact of cyanobacteria on Earth’s history.
Conduct a simple experiment to observe photosynthesis in action. Use a water plant like Elodea, place it in a clear container with water, and expose it to sunlight. Observe and record the oxygen bubbles produced. This hands-on activity will help you grasp the concept of photosynthesis and its significance.
Participate in a classroom debate about the Great Oxygenation Event. Split into two groups: one arguing that the event was beneficial for life on Earth, and the other arguing that it was catastrophic. This will encourage critical thinking and a deeper understanding of the event’s impact.
Create a 3D model or a detailed drawing that illustrates the process of endosymbiosis, where a cyanobacterium was engulfed by another microbe to become the ancestor of plant cells. Label the parts and explain the significance of this process in the evolution of complex life.
Investigate and present on the various environments where cyanobacteria are found today. Include examples such as oceans, freshwater bodies, soil, and extreme environments like Antarctic rocks. Discuss their ecological roles and how they continue to influence life on Earth.
Organism – An individual form of life, such as a plant, animal, bacterium, or fungus; a living being. – Humans are multicellular organisms with complex biological systems.
Cyanobacteria – A phylum of bacteria that obtain their energy through photosynthesis and are capable of producing oxygen; often referred to as blue-green algae. – The presence of cyanobacteria in the water can cause harmful algal blooms.
Mass extinction – An event that results in the extinction of a large number of species within a relatively short period of geologic time. – The Cretaceous-Paleogene extinction, which wiped out the dinosaurs, is one of the most well-known mass extinctions.
Earth’s history – The chronological development of the Earth from its formation to the present, including the changes that occurred over time. – Geologists study rock layers to understand Earth’s history and the processes that shaped it.
Complex life – Organisms that are made up of multiple cells and possess differentiated tissues and organs. – Animals, including humans, are examples of complex life forms.
Atmosphere – The envelope of gases surrounding a planet or celestial body, held in place by gravity. – Earth’s atmosphere consists primarily of nitrogen, oxygen, and trace amounts of other gases.
Oxygen-rich – An environment or atmosphere that has a high concentration of oxygen gas. – The oxygen-rich atmosphere created by early photosynthetic organisms allowed for the evolution of complex life forms.
Nitrogen – A chemical element (symbol N) that is a colorless, odorless, and relatively inert gas, making up about 78% of Earth’s atmosphere. – Nitrogen is an essential element for plant growth and is often added to soil as fertilizer.
Carbon dioxide – A colorless, odorless gas (chemical formula CO2) that is a natural component of the Earth’s atmosphere and is produced by burning fossil fuels, respiration, and other processes. – Increased levels of carbon dioxide in the atmosphere contribute to global warming and climate change.
Methane – A colorless, odorless gas (chemical formula CH4) that is the primary component of natural gas and is released during the decomposition of organic matter. – Cows produce methane as a byproduct of their digestion, contributing to greenhouse gas emissions.
