Describe how Absolute Dating/Numerical Age is used to evaluate geologic time.?

Question

Describe how Absolute Dating/Numerical Age is used to evaluate geologic time.?

Answer 1

Absolute dating is a process that assigns a numerical age to a rock (or a fossil) using radiometric isotopes. Since decay pairs have steady decay rates, they can have a known half life. By comparing percentages or parent and daughter isotope and the decay rate, the age can be determined, usually with minimal error.

Answer 2

Many elements have half lives, which simply means that element A will produce element B at a specific rate.  When half of element A is gone that is one-half life.  Half lifes for different elements (and compunds) vary from a few seconds to millions of years.  Finding the right element A and the right half life duration is where all this becomes useful for geologists.

Radiometric dating of sedimentary rocks can be done if some layers have some volcanic rocks interbedded in them.  Count the amount of element B vs element A in the volcanic rock will tell you how many half lives have transpired since the volcanic rock cooled.  Now multipy the number of half lives by the half life in years and you have the age of the volcanic rock.  This is also, presumably the age of the sedimentary rock in contact with the volcanic rock.

In environmental science we use half life of contaminants that are measured in soil today to calculate what the concentration may have been 10 to 20 years earlier when people may have been in contact with the soil when the contamiantion was much worse.