Mon Prof Augmenté
The Great Oxidation Event
Age 17 · Science
Open to everyone until Tuesday, November 17
To keep it, print it while it is open.
From about 2.4 billion years ago, cyanobacteria doing photosynthesis began releasing large amounts of oxygen into the oceans and atmosphere for the first time. That oxygen reacted with iron dissolved in seawater, forming insoluble iron oxide that settled on the seabed as the red layers of banded iron formations.
In the picture
- Cyanobacterial mat: microbes using sunlight, water and CO₂ for photosynthesis
- Oxygen bubbles: the O₂ released by photosynthesis entering the seawater
- Rust-red band: iron oxide that precipitated when oxygen met dissolved iron
- Pale grey band: a silica (chert) layer deposited between the iron layers
Examples
- An iron nail left in water slowly turns rust-red as oxygen oxidises the iron.
- Aquarium plants under a lamp give off small oxygen bubbles from their leaves.
Key takeaways
- Cyanobacterial photosynthesis caused oxygen to build up from about 2.4 billion years ago.
- Banded iron formations record dissolved ocean iron being oxidised and are a major source of today’s iron ore.
Quiz: The Great Oxidation Event (Age 17)
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What caused oxygen to start building up in the oceans and atmosphere from about 2.4 billion years ago?
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What happened when this new oxygen met iron dissolved in seawater?
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Why do banded iron formations matter to people today?
The answers, each with its explanation, are in the app. This quiz is free there while the lesson is in the free week.
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