According to wikipedia the reversals can take a while
>Some sources estimate the most recent four reversals took on average 7,000 years to occur. Clement (2004) suggests that this duration is dependent on latitude, with shorter durations at low latitudes and longer durations at mid and high latitudes. Others estimate the duration of full reversals to vary from between 2,000 to 12,000 years.
>Some sources estimate the most recent four reversals took on average 7,000 years to occur. Clement (2004) suggests that this duration is dependent on latitude, with shorter durations at low latitudes and longer durations at mid and high latitudes. Others estimate the duration of full reversals to vary from between 2,000 to 12,000 years.
- https://en.wikipedia.org/wiki/Geomagnetic_reversal
So maybe that's enough time for the biomass to adapt?