[tonmoy]

I’m not 100% sure I follow what you mean, but here is a link from NASA saying our magnetosphere protects the atmosphere from erosion https://science.nasa.gov/science-research/earth-science/eart...

[rustyhancock]

He's right the magnetosphere doesn't significantly protect our atmosphere. It probably reduces helium loss on earth and other lighter elements.

In addition to his Venus example, Mars lost its atmosphere because it's gravity was too small. Not because it lacks a magnetic field.