PerspectiveGeophysics

Revealing the dynamics of a large impact

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Science  18 Nov 2016:
Vol. 354, Issue 6314, pp. 836-837
DOI: 10.1126/science.aak9802

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Summary

Steady as a rock. We all know what to expect of rock. Rocks deform infinitesimally slowly. Earth scientists get excited at the prospect of “rapid” plate movements that average the same speed at which our fingernails grow. Humans don't make much impact on rocks, except at the most puny of scales. Sometimes nature does experiments for us that we could never do for ourselves: When a large meteorite hits the planet, interactions occur that are far outside our normal experience. The outer surface is deformed with a force and strain rate that we cannot begin to reproduce; rocks flow like fluid, very fast and on a huge scale. On page 878 of this issue, Morgan et al. (1) present results from a drilling expedition into the Chicxulub crater that reveal how the formation of peak rings in large impact craters occurs. Numerical simulations of the impact model the time scale of events: a rim of mountains, higher than the Himalayas, adjacent to a void 25 km deep and about 70 km wide, forming and collapsing within the first three minutes; the central fluidized peak rising and collapsing in minutes 3 to 4; and a shakedown period in minutes 5 to 10, leaving a shallow crater at the surface, an intensely deformed impact zone extending through the thickness of the Earth's crust and beyond, and the world changed forever.