RELATIVE AGE OF ROCKS

Lesson 10-2

Absolute or Relative?

•Anthony is the youngest.

•Melony is 4 years old.•Michael is older then Sasha.

•Sasha is 16 years old.•Ashley is older than Melony, but younger than Sasha.

Relative Dating•Used to determine the order of events and the relative age of rocks by looking at the position of rocks in a sequence

•Numbers are not used•Ex: “I am older than you.”

Law of Superpostion•In an undisturbed layer of rock, the oldest rocks are on the bottom and the younger rocks are toward the top

Original Horizontality•Layers of rock are initially deposited in flat, horizontal layers

Folding

Inclusion•Older rock included in the formation of newer rock

Cross-cutting•Intrusions

•igneous dikes ↑ and sills→•Faults

•When one geologic feature (younger) cuts across another geologic feature (older)

Unconformity•When erosion removes existing rock layers and causes a gap in the geological record

Index Fossils

ID ages of different rocks