  Large-scale volcanism has played a critical role in the long-term
habitability of Earth. Contrary to widely held belief, volcanism, rather than
impactors, has had the greatest influence on and bears most of the
responsibility for large-scale mass extinction events throughout Earth's
history. We examine the timing of large igneous provinces (LIPs) throughout
Earth's history to estimate the likelihood of nearly simultaneous events that
could drive a planet into an extreme moist or runaway greenhouse, leading to
the end of volatile cycling and causing the heat death of formerly temperate
terrestrial worlds. In one approach, we make a conservative estimate of the
rate at which sets of near-simultaneous LIPs (pairs, triplets, and quartets)
occur in a random history statistically the same as Earth's. We find that LIPs
closer in time than 0.1-1 million yr are likely; significantly, this is less
than the time over which terrestrial LIP environmental effects are known to
persist. In another approach, we assess the cumulative effects with simulated
time series consisting of randomly occurring LIP events with realistic time
profiles. Both approaches support the conjecture that environmental impacts of
LIPs, while narrowly avoiding grave effects on the climate history of Earth,
could have been responsible for the heat death of our sister world Venus.
