How would the atmosphere of the Earth differ if the Earth was much larger?
Answers
If the atmosphere kept the same volume , then the thickness shrinks. Also covering 4 times the area would mean average atmospheric pressure could halve if the earth has the same density.
Depends how much larger.
If it had been large enough to pull in and hold a lot of hydrogen and helium, it would have been a gas giant.
Less than that, perhaps little. But we have no examples we can see closely.
It would depend on how much larger, but there are a few guiding principles.
First of all, shockingly, you will find that Earth’s atmosphere covers the surface of Earth and not its volume. If you say double the diameter of Earth, the volume of stuff will multiply by 8, but the surface will only multiply by 4. This means that there is twice as much stuff to go around per unit of surface area. This would translate to a higher and therefore thicker atmosphere and deeper oceans.
Another less obvious consequence is that Earth would have been able to hold on to more and lighter molecules around the time it was formed. A bigger planet means stronger gravity and a much deeper gravity well that is much harder to escape. This will add to the previous effect, making the atmosphere even denser.
There is also a critical point where a planet becomes capable of holding on to hydrogen and helium efficiently. There’s a lot of that stuff, so a planet that can hold on to it will become very massive. This is what happened to places like Jupiter or Saturn.
All in all, we would be left with a much thicker and likely inhospitable atmosphere. The composition would also change, with lighter elements becoming more represented, and the layering becoming more pronounced.
Super-Earths and Mini-Neptunes have been found among the Exoplanets.