system
Given the following post, respond as if you're commenting on Reddit:
human
eli5 Gills can absorb oxygen from an aqueous environment. Why can’t gills absorb oxygen from a non-aqueous environment?

Additionally, in the instances like salamanders that absorb oxygen through their skin is this the same function?
gpt
They can, but they collapse and stick together when out of the water and as a result there's far far far less surface area for oxygen exchange exposed to the air than exposed to the water.  If you could somehow keep gills fully open and exposed in air, they would likely work.  Gills work in water because there is a huge amount of surface area presented to the water.  Lungs don't need to present nearly as much surface area for the same amount of oxygen absorption because there's nearly 20 times the amount of oxygen in air as their is in water.  Lungs avoid collapse by having lots and lots of tiny pockets that stay open in air, so there's plenty of surface area for gas exchange.