What is an atmosphere comparable to Earth's atmosphere?

[Lotto]

TL;DR

What does it mean when a planet have an atmosphere comparable to the Earth?

Does it mean that the atmosphere is made of the same atoms and molecules like our atmosphere and that it has the same spheres such as trophosphere? And that the temperatures in these spheres are also the same or very similar like here? And are distances between these spheres the same like here or are they adapted to the planet's size? What do you think?

 

[phinds]

What does it mean when a planet have an atmosphere comparable to the Earth?

VERY vague question but the most practical answer is simply "one in which humans can breath normally".

 

[Ibix]

Depends who says it and in what context. Presuming you're talking about exoplanets, it probably means that there's enough oxygen that the lead researcher reckons that bro, you could totally breathe that mix, and knows he's more likely to get more funding for more exoplanet research if he can sell it as earthlike...

 

[.Scott]

A comparison between Earth's atmosphere and that of other planets is usually tied to support for life.
So a planet with something "similar to Earth's" would include parts that are within 0 to 100 Celsius and contain some CO2 and perhaps N2. It could also contain a significant portion of O2, but at that point you would probably find the use of descriptions more exclamatory than "similar to Earth's" - since significant amounts of O2 aren't likely to persist without biological activity.
Nascent Oxygen can be detected in some exoplanets - but that can be from the ionization of H2O or CO2.
Here's an article describing how O2 can be produced from non-biotic chemical reactions.