In the science of geology, there are two main ways we use to describe how old a thing is or how long ago an event took place. When you say that I am 38 years old or that the dinosaurs died out 65 million years ago, or that the solar system formed 4.6 billion years ago, those are absolute ages.
There are absolute ages and there are relative ages. We use a variety of laboratory techniques to figure out absolute ages of rocks, often having to do with the known rates of decay of radioactive elements into detectable daughter products.
On other solid-surfaced worlds -- which I'll call "planets" for brevity, even though I'm including moons and asteroids -- we haven't yet found a single fossil.
Something else must serve to establish a relative time sequence. Earth is an unusual planet in that it doesn't have very many impact craters -- they've mostly been obliterated by active geology.
This all has to do with describing how long ago something happened. There are several ways we figure out relative ages.
The simplest is the law of superposition: if thing A is deposited on top of (or cuts across, or obliterates) thing B, then thing B must have been there already when thing A happened, so thing B is older than thing A.
If an impact event was large enough, its effects were global in reach.
Of course, this only works for rocks that contain abundant fossils.
When you talk about the Precambrian, Paleozoic, Mesozoic, and Cenozoic on Earth, or the Noachian, Hesperian, and Amazonian for Mars, these are all relative ages.
Relative-age time periods are what make up the Geologic Time Scale.
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.