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