Chicxulub << CHEEK shoo loob >> Crater is a large depression that overlaps the northern part of the Yucatán Peninsula of Mexico and the Gulf of Mexico . The crater is named after the nearby coastal town of Puerto Chicxulub. Scientists now understand that Chicxulub Crater formed around 65 million years ago when a large bolide (meteoroid) traveling through space crashed into Earth. Scientists believe the bolide was an asteroid or comet . The impact left a crater over 112 miles (180 kilometers) wide.
Scientists believe that the destruction from the impact caused the extinction of the dinosaurs and many other forms of life on Earth. The remains of the impact mark the boundary between the Cretaceous Period and Paleogene Period (also called the Tertiary Period) of the geologic time scale.
Scientists first determined that a large bolide struck the Earth when they discovered layers of sediment over a wide area of Earth that contained an unusually high abundance of the metallic element iridium . The layer dates from around 66 million years ago. Iridium is one of the rarest elements in Earth’s crust. But it is found in much higher abundance in meteorites, asteroids, and the cores of some comets.
Geologists later discovered the remains of the large Chicxulub Crater. However, they thought at first that the crater originated from volcanic forces. Years later, scientists discovered objects, called melt spherules, preserved in rocks in areas surrounding the crater. Scientists then realized the crater was caused by a bolide impact with Earth. As the object smashed into Earth, the energy released melted the surrounding rock. This molten rock was thrown high into Earth’s atmosphere. Much of it then cooled into small, round shapes. These spherules fell from the air piling up on the ground around the crater. Today, geologists understand that such melt spherules found at other locations are evidence of past impacts.
Geologists have found other kinds of evidence that showed the bolide impact was extremely violent. They discovered quartz rocks with certain distinctive features that were visible under a microscope. Geologists describe such quartz as shocked quartz. The features of shocked quartz can only happen as the result of a powerful impact. Geologists also discovered deposits of large boulders at sites around the Gulf of Mexico. They believe such deposits were formed when the bolide impact generated huge ocean waves that carried the boulders long distances.
Today, the Chicxulub Crater is buried by younger rocks and is not easily visible at the surface of Earth. However, a ring of sinkholes in the limestone of the Yucatán Peninsula roughly matches the boundary of the crater. The sinkholes, known locally as cenotes, formed when the limestone dissolves in flowing groundwater. Scientists believe that the bolide impact deformed the rock and changed the flow of groundwater to create the ring of cenotes. Geologists use instruments that measure the strength of Earth’s gravity and core samples taken through drilling to map the outlines of the crater in areas covered by the ocean. Earth’s gravity is slightly weaker in the rubble-filled crater compared with the rock that surrounds the region.
