Which bacteria was responsible for the first oxygen on Earth?

Which bacteria was responsible for the first oxygen on Earth?

• A. Cyanobacteria
• B. Algae
• C. Bacteria
• D. Fungi

Answer: (A)

The main idea is that oxygen in Earth’s early atmosphere came from a specific group of photosynthetic bacteria that release oxygen as a byproduct. Cyanobacteria perform oxygenic photosynthesis, using water as the source of electrons and releasing oxygen gas. This built up over time and led to the Great Oxygenation Event, transforming the atmosphere and enabling aerobic life to evolve. Other options aren’t correct because algae are eukaryotic organisms that also photosynthesize but appeared later in Earth's history, fungi aren’t photosynthetic, and the broad term “bacteria” doesn’t identify the particular group responsible for producing the oxygen.

The main idea is that oxygen in Earth’s early atmosphere came from a specific group of photosynthetic bacteria that release oxygen as a byproduct. Cyanobacteria perform oxygenic photosynthesis, using water as the source of electrons and releasing oxygen gas. This built up over time and led to the Great Oxygenation Event, transforming the atmosphere and enabling aerobic life to evolve. Other options aren’t correct because algae are eukaryotic organisms that also photosynthesize but appeared later in Earth's history, fungi aren’t photosynthetic, and the broad term “bacteria” doesn’t identify the particular group responsible for producing the oxygen.