Relative Dating Notes

A Little Bit of History…
• The history of geologic time begins with the human interest
in mining.
• Interests in rock units began to flourish with commercial
mining in the 1500s and 1600s
• People began to identify strata (rock layers) by the types of
fossils that were found within them.
• Two scientists were credited with contributing the most
research to this area -- Nicolaus Steno and James Hutton
Nicolaus Steno
Adapted two geologic principles
Law of Superposition : sedimentary rocks are
found with the oldest on the bottom and
youngest on top.
E.x. Paint layers
Principle of Original Horizontality: If left
undisturbed rock layers will stay in horizontal
James Hutton
18th-century Scottish
physician and farmer
 Studied his farm land for geologic changes
*The Present is the Key to the Past
 Principle of Uniformitarianism: geologic
processes from the past are the same as the
current geologic processes.
E.x. What happened then happens now
Relative Age: gives the age of a rock layer based on
the ages of layers around it (younger or older)
What sort of events can change the order of rock layers?
Law of Crosscutting Relationships
 Fault or body of rock is younger than any other body of rock
that it cuts through.
 Igneous intrusions that may be uplifted to the surface would
also be younger than the rock they push through
Unconformities- breaks
in geologic time where
rock layers erode away
or when sediment isn’t
Related flashcards

16 Cards

Sedimentary rocks

11 Cards


17 Cards

Sedimentary rocks

13 Cards

Granite domes

27 Cards

Create flashcards