Tree-rings reveal two strong solar proton events in 7176 and 5259 BCE.

The Sun sporadically produces eruptive events leading to intense fluxes of solar energetic particles (SEPs) that dramatically disrupt the near-Earth radiation environment. Such events have been directly studied for the last decades but little is known about the occurrence and magnitude of rare, extreme SEP events. Presently, a few events that produced measurable signals in cosmogenic radionuclides such as C, Be and Cl have been found.

Cosmogenic radionuclides reveal an extreme solar particle storm near a solar minimum 9125 years BP.

During solar storms, the Sun expels large amounts of energetic particles (SEP) that can react with the Earth's atmospheric constituents and produce cosmogenic radionuclides such as C, Be and Cl. Here we present Be and Cl data measured in ice cores from Greenland and Antarctica. The data consistently show one of the largest Be and Cl production peaks detected so far, most likely produced by an extreme SEP event that hit Earth 9125 years BP (before present, i.