Oxygen provides a necessary ingredient for nearly all forms of life on our planet, but it didn’t always exist here. For most of Earth’s history, oxygen was absent — only appearing in the last two billion years or so.
The “Great Oxygenation Event” that infused the gas into our atmosphere is commonly thought to have occurred around 2.4 billion years ago, when a rise in cyanobacteria released a huge amount of oxygen through photosynthesis. But it’s been difficult to get any more precise in terms of dating the first appearance of this life-giving gas; after all, how are scientists supposed to detect such a small quantity of oxygen from so long ago?
