Totally free chat with local aunties site - Relative dating using cratering distribution

It was introduced when the counters were dealing primarily with craters larger than 1 km, which roughly fit a -2 power law (more accurately, it is a -1.80 power law).

did not include discussion of crater counts below diameters of a few km, although some Viking images resolved craters of a few hundred meters in size.) Upper ~ 4 km above the Amazonian/Hesperian boundary, and 16 km for early Hesperian to early Noachian.

In these definitions, Tanaka assumed a -2 power law for the diameter distribution in that diameter range, an early approximation to the -1.80 power law used in that = 1.0 km)].

For example, if a certain region has had some erosive episode that removed all craters between 125 m and 500 m in size, the log-differential plot would show a dramatic downturn in that size interval, but he cumulative plot would merely flatten out.

The cumulative plot produces an artificial smoothing of the data, which looks good, but comes at the expense of actual information-display about the data.

Tanaka (1986, Table 2) defined crater density limits to the Amazonian, Hesperian, and Noachian relative-age eras, based on the previous work of Scott and Carr (1978) and Condit (1978), for the purpose of stratigraphic mapping of Mars.

That work parallels the development of terrestrial geology, in defining stratigraphy and relative time intervals long before the absolute time intervals could be measured.

Much later, the surface may be exhumed, as documented in various cases by Malin and Edgett.

In an ideal case, such a surface might then show vestiges of the degraded original craters (indicating the duration of exposure of the first surface) and a second population of fresh, small, sharp-rimmed craters formed since the recent exhumation event.

For example, bin divisions include 500 m, 707 m, 1 km, 1.4 km, 2 km, 2.8 km, and so on. In the text below, we will refer to three A branches of this size distribution.

Historically, the first branch recognized was the shallow branch, at diameters above about 1-2 km, recognized from craters counted on telescopic photos of the moon.

Tanaka defined each time interval in terms of cumulative counts of craters down to various diameters = 1 km.

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