Comets and asteroid fragments have hit all of the solar system’s planets and moons. We find impact craters everywhere.
Impacts shape the surfaces of worlds. Craters are the scars left on planetary landscapes by impacts and collisions. The size of an incoming object affects the size of the “splash” it makes and the amount of ejected material deposited around the site. Craters range from microscopic pits made by very small projectiles to huge holes in the ground made by very large objects.
On Earth, the largest objects to survive a trip through our atmosphere blast out huge impact scars. Early in its history, Earth was bombarded by countless incoming objects. Most of the craters left over from those ancient impacts have eroded away or been covered by lava flows and vegetation. Only a few obvious ones remain. The Moon and other airless worlds are pockmarked with craters of all sizes. Without erosion by wind and rain, those pits remain intact for billions of years and preserve the cratering history of the solar system.
When a large incoming body hits Earth, the result is a crater. The force and pressure of the collision vaporize parts of the meteorite, as well as the ground it hits. The impact blasts out the crater, melts some of the rock, and scatters fragments far and wide.
Meteorite Impacts Can Create Tektites
An impact digs up surface material and blasts it away. During large collisions, a lot of heat gets generated, which melts rock. Some of this “impact melt’ flows away, while some is blasted into the air with the rest of the ejected rocks and meteorite fragments. As the airborne splash of hot liquid rock fall back to Earth’s surface, they cool into interesting shapes. These bits of melted earth are tektites, and each sample contains different materials formed under unique conditions.
Tektites are found in a few scattered locations on Earth. These Bediasites were found in Texas. The Libyan Desert Glass is strewn across the northern African deserts. Moldavites come from the Czech Republic and neighboring countries.
An Impact Killed the Dinosaurs
Sixty-five million years ago, the dinosaurs and other animals died off. This extinction probably happened because a huge asteroid or comet struck the ancient shoreline of the Yucatán Peninsula in Mexico. It hit with the force of a 100-million-megaton bomb and made a crater 60 miles (97 km) across.
The impact raised dust that blocked incoming sunlight. Temperatures fell, and plant photosynthesis was interrupted. The hostile conditions and food shortages helped kill off most of Earth’s animals.
We find evidence for the impact in the K/T Boundary, a layer of clay deposited around the time of the extinction. It is rich with rare elements like iridium that most likely originated in a rock from space.
A huge Canadian nickel mine lies at the site of an ancient asteroid impact.
Almost 2 billion years ago, an asteroid crashed into central Canada, near the current town of Sudbury, Ontario. It vaporized a chunk of Earth’s crust and created a crater 12 miles (19 km) deep. The impact tore away rock layers and exposed Earth’s upper mantle. This allowed metal-bearing magma to flow to the surface. Today we find rich deposits of nickel, copper, and platinum on the site. Near the point of impact, rock melted instantly, flowed as liquid, and cooled into black melt glass. The impact also tossed out fragments of bedrock and pieces of the meteorite, which fell back to the area surrounding the crater.
Shattercones: Proof of an Ancient Impact
Shattercones are shock waves preserved in stone. They occur when an impact blasts into layers of bedrock and puts the rock under tremendous pressure. It shatters, creating three-dimensional cone-shaped patterns. The tips of the cones point back to the impact source.
When Meteorites Attack!
In 1954, a fragment of an asteroid crashed through the roof of a house in Sylacauga, Alabama. It bounced off the ﬂoor and hit Ann Hodges while she was napping on her couch. She was the ﬁrst person documented to have been struck by a meteorite. Mrs. Hodges sold autographed pictures of herself holding the meteorite under the damaged ceiling. The rock is now on display in the University of Alabama’s Natural History Museum.
A Meteorite Meets a Carport
Impacts come when you least expect them. In 1973, a carport roof in San Juan Capistrano, California, took a hit from an asteroid fragment. Owner George Stinchcomb reported hearing a sound like a gunshot in the middle of the night. The next morning, he found an egg-size meteorite that crashed through the carport roof onto the concrete ﬂoor.