Answer :

First, they can describe how old fossil is by just looking at the layer where the fossil remain, the deeper the fossil, the longer the time way back that organism has live.

Second, Radiometric Measuring, is how they calculate how the fossil has been decays over time.
 Hope this help.

Answer:

relative and absolute dating

Explanation:

Two methods of dating fossil fuels are -

a) Relative Dating  and b) Absolute Dating

a) Relative Dating - In this method,  unknown age of fossil A is determined by comparing it with the known age of fossil B via correlation . Such " fossils B" are known as index fossils. These index fossils belong to a specific age group.

Some common example of index fossils are -

brachiopods,

trilobites, and

ammonites

b) Absolute Dating - In this method, the age of rock is determined through radiometric dating methods. Here, instead of dating the fossil itself, the rock or volcano layer above and below the fossil is dated for determining a rage of date.