Impact craters are geologic structures formed when a large meteoroid, asteroid or comet smashes into a planet or a satellite.Impact craters are geologic structures formed when a large meteoroid, asteroid or comet smashes into a planet or a satellite. Often hard to recognize on Earth because of the effects of weathering and erosion Often hard to recognize on Earth because of the effects of weathering and erosion Impact craters are divided into two groups based on morphology: simple craters and complex craters.Impact craters are divided into two groups based on morphology: simple craters and complex craters.

Simple and Complex Crater Simple Craters - are meteorite impact craters of relatively small diameter, characterized by a uniformly concave-upward shape and a maximum depth in the center, and lacking a central uplift.

Simple and Complex Crater Complex craters are a type of large impact crater morphology. The central peak or peak ring of the complex crater is formed as the initial (transient) deep crater floor rebounds from the compressional shock of impact. Slumping of the rim further modifies and enlarges the final crater.

Parts of an Impact Crater

Floor — The bottom of a crater, either bowl-shaped or flat, usually below the level of the surrounding ground. Central peaks — Peaks formed in the central area of the floor of a large crater. Walls — The interior sides of a crater, usually steep. They may have giant stair-like terraces that are created by slumping of the walls due to gravity. Rim — The edge of the crater. It is elevated above the surrounding terrain because it is composed of material pushed up at the edge during excavation. Ejecta — Rock material thrown out of the crater area during an impact event. It is distributed outward from the crater's rim onto the planet's surface as debris. It can be loose materials or a blanket of debris surrounding the crater, thinning at the outermost regions. Rays — Bright streaks extending away from the crater sometimes for great distances, composed of ejecta material.

Meteor Crater in Arizona (also know as Barringer Crater) was the first-recognized terrestrial impact crater. It was identified in the 1920s by workers who discovered fragments of the meteorite impactor within the crater itself. Examples of Terrestrial Impact Craters Approximately 1.2 km (0.75 mi.) wide and 200 m (650 ft.) deep. Created about 50,000 years ago by a 50 m (150 ft.) meteorite.

Examples of Terrestrial Impact Craters This three-dimensional map of local gravity and magnetic field variations shows a multiringed structure called Chicxulub named after a village located near its center. The Chicxulub crater is an ancient impact crater buried underneath the Yucatán Peninsula in Mexico. Its center is located near the town of Chicxulub, after which the crater is named. This caused global temperatures to plunge near freezing. Half of the species on Earth became extinct including the dinosaurs.

Examples of Terrestrial Impact Craters In Aorounga, Chad, Africa The impact of an asteroid or comet several hundred million years ago left scars in the landscape that are still visible in this spaceborne radar image of an area in the Sahara Desert of northern Chad. The original crater was buried by sediments, which were then partially eroded to reveal the current ring- like appearance.

Examples of Terrestrial Impact Craters Wolfe Creek, Australia Wolfe Creek is a relatively well-preserved crater that is partly buried under wind blown sand. The crater is situated in the flat desert plains of north- central Australia. Its crater rim rises ~25 meters (82 feet) above the surrounding plains and the crater floor is ~50 meters (164 feet) below the rim.

Examples of Terrestrial Impact Craters Roter Kamm, South West Africa/Namibia Located in the Namibia Desert, the raised crater rim is clearly visible against darker background vegetation. Target rocks include primarily Precambrian crystalline rocks and modest amounts of younger sedimentary rocks. Outcrops of impact melt breccias are found exclusively on the crater rim. The crater floor is covered by broad, shifting sand dunes.