If +/- 4million is the error, what is the total error?

Question

This is for calculating the total age of a rock in biology class.

Answer 1

You already know the error.  It is ±4 million.  I think what you really meant to ask for is the age of the rock.  If the measured age in years is A, then the proper age to report is

 

A ± 4,000,000 years

 

For example, suppose you measured the age to be 3.2 billion years, with an uncertainty of ±4,000,000 years.  You would report the measurement as

 

3,200,000,000 ± 4,000,000 years

 

where the uncertainty of 4,000,000 years depends on the method used to measure the age.  Are you working with radiometric dating?