How do high-flying airplanes get enough oxygen for their engines

This week's question comes to us from Terry Rowsell, in St.John's, Newfoundland. He asks:

Airplane engines need oxygen for combustion. But where do they get oxygen at 40,000 feet? 

Ghazal Geshnizjani, a research associate professor at the Waterloo Centre for Astrophysics at the University of Waterloo, explains that engines can concentrate the thin air to generate enough oxygen for combustion.

The resistance of the air is working against the airplane, and is trying to slow it down. At high altitude, there isn't much resistance because of the lack of oxygen. That makes it easier for the plane to fly, which means the engines don't need to push very hard to maintain high speeds.  

They do still need oxygen, though, even at for low power levels. Fortunately, aircraft engineers have designed engines that solve this dilemma. Jet engines compress the air internally, making it much thicker and providing adequate oxygen for combustion.