[htag]

Yes, our magnetosphere has had extended periods (~hundreds of years) of being in a weakened state without disrupting all life on Earth. Our empirical evidence on the size of the impact is limited, mostly due to how long ago it was. It was a big enough impact that it did leave evidence.

It's not an humanity destroying event, but it is a big stressor on a world already going through a lot.

[chasil]

It's actually measured in thousands of years.

"Other sources estimate that the time that it takes for a reversal to complete is on average around 7,000 years for the four most recent reversals."

A range of 2k-12k is also in the introduction.

https://en.wikipedia.org/wiki/Geomagnetic_reversal