Question

What is responsible for changing the Earth's atmosphere to an oxygen rich originally?
Responses

Volcanoes
Volcanoes

Plants
Plants

Cyanobacteria
Cyanobacteria

Comets

Answer 1

The primary responsible factor for changing the Earth's atmosphere to an oxygen-rich one is **Cyanobacteria**. These microorganisms, which were among the first photosynthetic organisms on Earth, produced oxygen as a byproduct of photosynthesis. This process, known as the Great Oxygenation Event (approximately 2.4 billion years ago), dramatically increased the oxygen concentration in the atmosphere and transformed it into a more oxygen-rich environment.