These findings led to an extensive search for a large impact crater that is 65 million years old. Seven researchers finally located the impact site on Mexico's Yucatan Peninsula.

    It is a huge buried impact crater that is called Chicxulub, a Maya word that roughly translates as "tail of the devil." The crater, now buried beneath a kilometer-thick sequence of sediments, has been imaged using geophysical techniques that allow us to visualize underground structures. It appears to have a diameter of approximately 180 km, which makes it one of the largest confirmed impact structures on Earth. Only Sudbury in Canada and the Vredefort structure in South Africa could potentially be larger.

A paleogeographic reconstruction of the continents 65 Ma showing the impact location in red
and modern continents then submerged in light blue.

    The asteroid or comet that produced the Chicxulub crater was roughly 10 km in diameter. When an object that size hits Earth's surface, it causes a tremendous shock wave while transferring energy and momentum to the ground. The impact was similar to a large explosion, although the energy of the Chicxulub impact dwarfs anything modern civilization has experienced. The energy of the impact was comparable to 100 million megatons of TNT, 6 million times more energetic than the 1980 Mount St. Helens volcanic eruption. The impact ejected rock from several kilometers beneath the surface of the Earth and carved out a bowl-shaped crater nearly 100 km in diameter. In addition, the shock of the impact produced magnitude-10 earthquakes, which were greater than the magnitude of any we have ever measured in modern times.

    The initial bowl-shaped crater was very unstable, and its walls quickly collapsed along a series of faults that enlarged the final diameter to be approximately 180 km.  At the same time, the rock that had been compressed beneath the crater by the impact rebounded, producing a peak-ring structure in the crater's center. These dramatic changes, which rapidly transported huge volumes of rock over distances of tens of kilometers, occurred within only a few minutes.

Peak Ring Crater Animation

    Because the impact site was in a shallow sea, water may have rushed in to fill the circular depression. Kilometer high waterfalls may have tumbled over the rim of the crater and roared furiously across the floor of the crater.

    Because seawater filled and covered the crater, sediment on the bottom of the sea soon buried the impact scar.  The crater is no longer visible today, even when standing directly over it.

    In more recent times, the impact crater has affected the circulation of groundwater on the Yucatan Peninsula.  This groundwater, has in some areas, dissolved the limestone in the Yucatan peninsula.  Below ground, this has produced caves. At the surface, this has produced cenotes which are groundwater springs. The cenotes form a ring, like a blue pearl necklace,  that is nearly coincident with the rim of the Chicxulub structure and is the only visible feature on the surface to indicate a huge crater lurks below.

    The explosion that produced the Chicxulub crater excavated a huge amount of material, which was then ejected upwards. Most of the debris was deposited as a blanket of material that covered North America and possibly South America.  Near the impact crater the debris is tens to hundreds of meters thick, while as far away as Colorado (over 2000 km distance), the debris is still a centimeter thick (see photograph below).  Additional material was lofted in an expanding, vapor-rich plume that included gas from the vaporized asteroid or comet. This plume rose  far above the Earth's atmosphere, enveloping it, and eventually depositing a thin layer of debris around the entire world.

Photograph of the K/T boundary sequence at Raton Basin in Colorado. The light gray unit in the middle of the photograph (marked with the red knife) is composed of two layers that mark the K-T boundary. A coal deposited in the Tertiary Period, after dinosaurs disappeared, is deposited on top of the K-T boundary layers.

Diagram of the Raton Basin as it appeared before the impact event. The mudstone and siltstone at the bottom of the above Raton Basin photograph were deposited in an environment such as this.
Adapted from Pillmore et al. in GSA Field Guide 1999.