4 absolutes applied to dating
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.
Relative-age time periods are what make up the Geologic Time Scale.But when the argument was negative, we change the sign; namely, we changed the "understood" "plus" into a "minus".This leads to one fiddly point which may not come up in your homework now, but will probably show up on tests later: When you are dealing with variables, you cannot tell the sign of the number or the value that is contained within that variable.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.The more fossils you find at a location, the more you can fine-tune the relative age of this layer versus that layer.