Science Buddies: "Ask an Expert"

Hello,
I was wondering-
Hypothetically speaking- if we would find another planet, the size of erth, with atmosphere as dense as earth's atmosphere is, and we would insert (in some hypothetical way) nitrogen, oxygen and co2 in the quantity they are found on erth, and (again in a hypothetical way) we would "get out" whatever gases are in that planet's atmospher. would it be possible to create an environment in which we could breathe?

Thank you!

The size of a planet is not the only thing that matters; its density matters too. The gravitational force from the planet has to be able to maintain an atmosphere. If we did find and Earth-like planet with the same size and density, we would be able to breathe if we replicated Earth's atmosphere on the new planet. What you're describing is basically building an artificial Earth.