Relative (Date) Age
and
Absolute (Date) Age
Relative (Date) Age
• Relative age means
the age of one object
compared to the age
of another object.
• Relative age does not
tell the exact age of
the object
• Uses terms such as
before and after, older
and younger, 1st, 2nd ,
and 3rd
Relative age
• Can you give me an example of relative
age?
• Hint: Sedimentary Rock Beds
Law of Superposition
• The law of superposition states that rock
layers at the bottom of a rock bed is
normally older than the rock layers at the
top of a rock bed
Law of Superposition
• Since rock layers
at the bottom of a
sedimentary rock
bed are older, you
can also say that
fossils found in
those layers are
about the same
age
Index fossils
• Index fossils are fossils
of organisms that lived
only during a short part
of Earth’s history.
• Index fossils are:
– Wide spread
– Unique
– When found helps
scientist identify age.
• An example is the
trilobite.
Absolute (Date) Age
• It is the age of a rock unit,
fossil or geologic event
expressed in units of time,
such as years.
• Absolute age puts a
number on it!!
– A good example is your birthday.
• Types of absolute age are:
– Radiometric dating
– Carbon 14 dating
Ice Cores
• Cylinder of ice removed from an ice sheet
• Deep deposits of ice and snow
• Scientists count the layers of snow just as
they count the layers in a rock bed
• Scientist analyze the data to find how
earths atmosphere has changed and what
type of plants lived in the past