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Earth and Space Sciences · 术语表

什么是 Crater dating; production and chronology functions; equilibrium density？

又称： crater dating · crater production function · crater chronology function · crater equilibrium density

Definition 26.6 University Earth and Space Sciences — Year 3 · 第 26 章 — Planetary Interiors and Surfaces

Crater dating is the determination of the age of a surface from the density of its craters. The crater production function is the shape of the size–frequency distribution of the craters a surface acquires, $F(D) = N(D)/N(1\,\mathrm{km})$ , assumed the same at every age. The crater chronology function $N_1(T)$ is the number of craters of $1\,\mathrm{km}$ and more per unit area accumulated in a time $T$ . A surface is at the crater equilibrium density for craters of a given size when each new crater erases, on average, as many old ones as it adds: their number no longer grows.

Left: isochrons of Mars, the cumulative densities of craters on surfaces 0.1, 1, 3.5 and 4 billion years old, with the equilibrium density (dashed), which caps every count: on a surface 4 billion years old the craters smaller than about 0.7\, km are at equilibrium and no longer record the age. Right: the chronology functions of Mars and of the Moon, the number of craters of 1\, km and more per square kilometre against the age of the surface. — Left: isochrons of Mars, the cumulative densities of craters on surfaces 0.1, 1, 3.5 and 4 billion years old, with the equilibrium density (dashed), which caps every count: on a surface 4 billion years old the craters smaller than about $0.7\,\mathrm{km}$ are at equilibrium and no longer record the age. Right: the chronology functions of Mars and of the Moon, the number of craters of $1\,\mathrm{km}$ and more per square kilometre against the age of the surface.

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