Each original isotope, called the parent, gradually decays to form a new isotope, called the daughter.
Each isotope is identified with what is called a ‘mass number’.
With this system, an event that occurred in 1000 B.
The earliest evidence of writing anywhere in the world only goes back about 5000 years.
All trees of the same species in an area usually have roughly the same pattern of growth.
Since weather patterns tend to run in cycles of a number of years, the sequence of tree-rings in a region will also reflect the same cycling, as illustrated by the graph below.
Sedimentary rock is made of particles derived from other rocks, so measuring isotopes would date the original rock material, not the sediments they have ended up in.
However, there are radiometric dating methods that can be used on sedimentary rock, including luminescence dating.
This is different to relative dating, which only puts geological events in time Most absolute dates for rocks are obtained with radiometric methods.
These use radioactive minerals in rocks as geological clocks.
All radiometric dating methods measure isotopes in some way.
Most directly measure the amount of isotopes in rocks, using a mass spectrometer.
These rates of decay are known, so if you can measure the proportion of parent and daughter isotopes in rocks now, you can calculate when the rocks were formed.