system
Given the following post, respond as if you're commenting on Reddit:
human
Is a geode filled with prehistoric air, or is it a vacuum?
gpt
Whatever gasses are freed when the Geode-to-be cools will be in there for quite some time.
Very little pre-historic "air" will remain, even if there is some somehow trapped it will take part in whatever chemical reaction will take place in the "making" of the geode, fueled by immense pressure and heat.

The Atoms will stay intact so one could argue that we are breathing oxygen that probably was within a geode, being part of a Silicium-oxide molecule for example.
Since Atoms are rather difficult to break one could argue that any scenario you can think of for any chemical you deal with (by eating them for example) was true at one point.
Eat some noodles and the carbon might have been part of a diamond 400 million years ago while the hydrogen might have been within the hull of the "Hindenburg" and before that it was part of a water molecule in the tethys sea.


So one could say yes and no to your question: The gasses trapped in the geode where part of the atmosphere at some point in the past but the chemical make up in the geode does not represent anything close to the chemical make up of the atmosphere.