Farouk El-Baz

Document Type

Article

Publication Date

1977

Abstract

The lunar scene is a continuous panorama of ancicnt lmpact Physiography. Multi- ringed circular basins and smaller craters scar the Moon's ighlands and provide evidence of a violent ecarly history. Basin formation, the major material-transporting mechanism on the Moon, produces a decp inner depression, one or more benches, a basin rim, and radially lineated ejecta. Study of lunar photographs indicates that, c relative age scale, subdued basin and crater fcatures arc older representations younger, well-preserved forms. Absolute agel dating of returned samples makes feasible to calibrate this rclativc age scalc, All the larger basins were formed during pre-Nectarian, Nectarian and Imbrian times, i.e. 4.6 3.9 Ga ago. on of it Following this major sculpturing episode, and during the Imbrian and Fratos- thenian times, mare volcanism became the most important mode of deposition of lunar surface materials. Basaltic lavas from dccp-scatcd sources fowcd to partially fill the t ımpact basins and cover their periphcral troughs and surrounding lowlands between 3,8 and 3.2 Ga ago. This occurred more frequently on the near side than on the far sidc, probably becausc the farside crust is thicker During the past 1 Ga, i.c. Copernican timc, only a small number of craters were formed in both highland and mare rocks. Successes and failures JO E photogeologists in studying lunar stratigraphy providc the nccessary lessons for understanding m [history of thc terrestrial planets, This is particularly true since both Mars ana Mcrcury display many types of features in T common with the Moon.

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