The
Laschamp event was a short
reversal of the Earth's magnetic field. It occurred 41,400 (±2,000) years ago during the
last ice age and was first recognised in the late 1960s as a geomagnetic reversal recorded in the Laschamp lava flows in the
Clermont-Ferrand district of France. The magnetic excursion has since been demonstrated in geological archives from many parts of the world. The period of reversed magnetic field was ~440 years, with the transition from the normal field lasting ~250 years. The reversed field was 75% weaker whereas the strength dropped to only 5% of the current strength during the transition. This resulted in greater radiation reaching the
Earth, causing greater production of
beryllium 10 and higher levels of
carbon 14.