Q1/Q3 W6 The Great Oxidation Event

Click the plus sign to explore how the atmosphere has changed

Click the plus sign to learn about cyanobacteria

Click the plus sign to learn about the evidence of oxygen in the ocean

Click the plus sign to watch a video on the Great Oxidation Event

This graph is a 4.6-billion-year timeline of Earth's atmosphere. Read it from left (the past) to right (today). Each color is a different gas, and its height shows its percentage in the atmosphere at that time.

Turn on captions for the video by clicking the CC button on the bottom.

Banded Iron Formations

Earth's early oceans were filled with dissolved iron. When the first photosynthetic bacteria began releasing oxygen, it mixed with the iron and caused it to rust. This rust sank to the ocean floor, forming layers that eventually hardened into reddish rocks. We can still see these Banded Iron Formations today, and they are the best proof we have of when oxygen first appeared on our planet.

Cyanobacteria

Cyanobacteria are prokaryotes (single-celled organisms without a nucleus) and were among the first to perform photosynthesis, producing oxygen that gradually changed Earth’s ocean atmosphere. Many grow in chains of connected cells, where each cell is still an individual organism. These chains and mats trapped sediments, forming stromatolites, some of the oldest evidence of life on Earth.

Just like plants, cyanobacteria use photosynthesis to make oxygen and sugar.