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The annual 14 C data in tree rings is an outstanding proxy for uncovering extreme solar energetic particle (SEP) events in the past. Signatures of extreme SEP events have been reported in 774/775 CE, 992/993 CE, and ∼660 BCE. Here, we report another rapid increase of 14 C concentration in tree rings from California, Switzerland, and Finland around 5410 BCE. These 14 C data series show a significant increase of ∼6‰ in 5411-5410 BCE. The signature of 14 C variation is very similar to the confirmed three SEP events and points to an extreme short-term flux of cosmic ray radiation into the atmosphere. The rapid 14 C increase in 5411/5410 BCE rings occurred during a period of high solar activity and 60 years after a grand 14 C excursion during 5481-5471 BCE. The similarity of our 14 C data to previous events suggests that the origin of the 5410 BCE event is an extreme SEP event., (© 2021. The Authors.)