Space/Science — HabitableZone

Space/Science » in reply to Re: So um, could it be that some (or even much)

Age and Scale
Nick Hoffman — (archived)

Measuring age is a tricky thing on Mars, and largely relies on crater counting. This is constrained by analogy with Moon, but is unknown in reality.

The major problem is not so much that we don't know the absolute age of a surface with yea many craters on it, but that the age depends on the scale we look at.

Large old craters poke through the surface, implying old ages, but that surface may be younger, in fact by definition, the entire surface of Mars has an age of zero, since various processes are working right now.

Numerous studies have shown that depending on the scale we look at, we come up with different ages:-

A Noachian (3.7 Ga) terrain, defined by numerous large craters > 50 Km may have buried within it an even older crater population of craters ~ 200 km (e.g. Frey et al. 2002). Simultaneously, it may have sub-areas of ~ 10 km^2 within it that are younger, e.g Hesperian (3.0 to 3.5 Ga) Volcanic features, Amazonian (0.7 to 1.8 Ga) sediments in patches of ~ 5 km^2, and recent hillslope weathering on a metre to km scale.

The trick is to identify the main processes working to physically modify the surface, and when they occurred (When is defined by crater counts or other indirect means).

All dates are rubbery, but they're all we've got...

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