With this kind of uncertainty, Felix Gradstein, editor of the For clarity and precision in international communication, the rock record of Earth's history is subdivided into a "chronostratigraphic" scale of standardized global stratigraphic units, such as "Devonian", "Miocene", " ammonite zone", or "polarity Chron C25r".
Unlike the continuous ticking clock of the "chronometric" scale (measured in years before the year AD 2000), the chronostratigraphic scale is based on relative time units in which global reference points at boundary stratotypes define the limits of the main formalized units, such as "Permian".
Paleontologists have examined layered sequences of fossil-bearing rocks all over the world, and noted where in those sequences certain fossils appear and disappear.
When you find the same fossils in rocks far away, you know that the sediments those rocks must have been laid down at the same time.
The science of paleontology, and its use for relative age dating, was well-established before the science of isotopic age-dating was developed.
Nowadays, age-dating of rocks has established pretty precise numbers for the absolute ages of the boundaries between fossil assemblages, but there's still uncertainty in those numbers, even for Earth.
Venus, Io, Europa, Titan, and Triton have a similar problem.
On almost all the other solid-surfaced planets in the solar system, impact craters are everywhere. We use craters to establish relative age dates in two ways.If an impact event was large enough, its effects were global in reach.For example, the Imbrium impact basin on the Moon spread ejecta all over the place.Just like a stack of sedimentary rocks, time is recorded in horizontal layers, with the oldest layer on the bottom, superposed by ever-younger layers, until you get to the most recent stuff on the tippy top.On Earth, we have a very powerful method of relative age dating: fossil assemblages.This all has to do with describing how long ago something happened. There are several ways we figure out relative ages.