Relative dating cratering distribution
Craters are roughly circular, excavated holes made by impact events.This portion of the Moon is covered by numerous circular holes.Geologic processes have not erased the craters with time. The shock wave fractures the rock and excavates a large cavity (much larger than the impactor).The impact sprays material — ejecta — out in all directions.Copernicus is a large crater (93 kilometers or 60 miles wide) on the Moon. This crater is about 20 kilometers (12 miles) across and has a large central peak and terraces around its rim.The inner walls of the crater have collapsed to form a series of step-like terraces, and a central peak is visible in the center of the image. The ejecta blanket has lobes, which may indicate wet material was ejected, suggesting that subsurface water or melted ice was mixed into the debris.
The circular shape is due to material flying out in all directions as a result of the explosion upon impact, not a result of the impactor having a circular shape (almost no impactors are spherical).Approximately 80% of Earth's surface is less than 200 million years old, while over 99% of the Moon's surface is more than 3 billion years old.Essentially, the Moon's surface has not been modified since early in its history, so most of its craters are still visible. Barringer Crater (Meteor Crater) in Arizona, United States, is a simple crater created when a 50-meter-wide (160-foot-wide) iron-rich meteroid struck Earth's surface about 50,000 years ago — a very recent event to a geologist.The largest impact basin on the Moon is 2500 kilometers (1550 miles) in diameter and more than 12 kilometers (7 miles) deep.Large impact basins are also found on other planets, including Mars and Mercury.