It turns out that polar ice cores do contain large amounts of sulfur dating to 536, a distinct signal of a major eruption. But which volcano went off at the time remains a mystery. There is no known written record from anyone living close to the eruption—Iceland, where it may have occurred, was not yet populated.
Large volcanic eruptions cool Earth’s climate by injecting tiny particles of sulfur high into the atmosphere, where they reflect a portion of incoming sunlight back into space for periods of months or years. The 1257 eruption of the Samalas volcano in Indonesia dwarfed others in recent
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