73,000 BP - Volcanic Eruptions

Graph of volcanic activity Approximately 73,000 years ago, an Indonesian volcano known as Toba erupted with enough force to send more than 600 cubic miles of volcanic material into the atmosphere. Detected on this graph, which displays volcanic sulfate levels between 20,000 and 110,000 years ago, Toba was the largest eruption of the past 500,000 years. (The seemingly larger spike at about 53,000 years ago involved a series of smaller eruptions on Iceland, which is far closer than Toba is to Greenland, where this core was taken.) Such violent, so-called caldera eruptions can drastically alter global climate, by spewing so much ash and sulfur compounds into the atmosphere as to block sunlight and lower temperatures worldwide. Ice cores offer scientists the best means available to learn how past eruptions have affected climate—and thus to predict the impact that future ones might have. If an eruption on the order of Toba, which climatologists believe may have led to as much as several centuries of cold climatic conditions, were to occur today, it could seriously disrupt life on Earth.

Graph modified from:
Zielinski, G.A., P.A. Mayewski, L.D. Meeker, S. Whitlow, and M. Twickler, 1996a, A 110,000-year record of explosive volcanism from the GISP2 (Greenland) ice core, Quaternary Research, 45, 109-118.