Relative dating the rocks

13 Dec

Free 5-day trial Geologic time extends back 4.6 billion years.

Because the earth is so old and rocks formed millions of years ago, geologists needed a way to date rocks and rock units called strata.

Others measure the subatomic particles that are emitted as an isotope decays.

Some measure the decay of isotopes more indirectly.

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’.

When ‘parent’ uranium-238 decays, for example, it produces subatomic particles, energy and ‘daughter’ lead-206.

Isotopes are important to geologists because each radioactive element decays at a constant rate, which is unique to that element.

relative dating the rocks-39relative dating the rocks-47

However, there are radiometric dating methods that can be used on sedimentary rock, including luminescence dating.Law of superposition: This is one of the most basic techniques of relative dating geologists use.This principle says that the oldest rock layer is always on the bottom and layers above it get progressively younger.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.Because of their unique decay rates, different elements are used for dating different age ranges.