Time and Geology
Relative Age Dating
• In trying to understand the creation of the geology of an area
prior to the 20th century techniques, a method referred to as
Relative Age Dating was used.
• Relative Age refers only to the order (i.e. older or younger) of
particular events, not the actual age of an event.
• Relative Age Dating is process involving the application of
good observation skills and common sense to deduce the
sequence of events in a particular area. True age is not
relevant.
Principle of Original
Horizontality
• This principle is based upon the observation that sediment
usually accumulates or is deposited in horizontal layers
• X
Principle of Superposition
• This states that in a layered sequence of sedimentary rocks,
the oldest layer is on the bottom and become progressively
younger toward the top.
Principle of Lateral Continuity
• This principle state that a layer of sedimentary rock or
sediment extends laterally in all directions until it thins out or
terminates
Principle of Cross-Cutting
Relationship
• Any event (e.g. fault: intrusions) that cuts through a rock or
another event must be younger that the event it cuts through.
Principle of Inclusions
• This states that inclusions (fragments of rock) of one rock
found in another are always older than the rock they are
found in.
The Principle of Faunal
Succession
• This principle proposes that fossil assemblages (groups of
fossils) succeed one another through time in a regular and
predictable order, from least complex to most complex.
So what has happened here?
What is the oldest rock?
What is the youngest rock?
The end result