  The origin of the Chicxulub impactor, which is attributed as the cause of the
K/T mass extinction event, is an unsolved puzzle. The background impact rates
of main-belt asteroids and long-period comets have been previously dismissed as
being too low to explain the Chicxulub impact event. Here, we show that a
fraction of long-period comets are tidally disrupted after passing close to the
Sun, each producing a collection of smaller fragments that cross the orbit of
Earth. This population could increase the impact rate of long-period comets
capable of producing Chicxulub impact events by an order of magnitude. This new
rate would be consistent with the age of the Chicxulub impact crater, thereby
providing a satisfactory explanation for the origin of the impactor. Our
hypothesis explains the composition of the largest confirmed impact crater in
Earth's history as well as the largest one within the last million years. It
predicts a larger proportion of impactors with carbonaceous chondritic
compositions than would be expected from meteorite falls of main-belt
asteroids.
