Question: What are the 3 types of rocks and what is the rock cycle?
Answer: … … …

What is Dating?
 When geologists date rocks, they are determining how long ago they formed.
 Two ways to do this:
 Relative Dating
 Absolute Dating

Relative Dating
 Determining how old something is compared to something else
 Use words like “ older ” or “ younger ” instead of exact numbers

Rules of Dating
 two rules for dating rocks:
1.
Stuff on the bottom is oldest and the stuff on the top is youngest
 This is called the
Law of Superposition
 This only works for sedimentary rocks
(sometimes lava flows)

Order these layers from oldest to youngest
Youngest layer
Oldest layer

Rules of Dating
 two rules for dating rocks:
2. If a fault or another rock cuts through a layer it happened after (and is younger than) the layer
 This is called the
Law of Cross-Cutting Relations

Order the events from oldest to youngest
YOUNGEST LAYER/EVENT
Fault
Gray Layer
Multicolored layer
Spotted Layer
OLDEST LAYER/EVENT

Absolute Dating
 Determining how old something is
 Use numbers (in millions of years, mya)
 Only works for
Igneous Rocks

How Absolute Dating Works
 When magma/lava cools, radioactive elements are incorporated into the minerals
 Examples:
-- Potassium 40
-- Uranium 235

How Absolute Dating Works
 These elements begin to decay at a known rate starting when the rock cools
 We can measure how much of the element is left
 Tells us how much time has passed since the rock formed.

What can we learn from this?
 Geologist
 T-Rex Fossil
Basalt, dated to 80 mya
Sandstone
Basalt flow, dated to 100 mya
So when did this T-Rex live?
Between 100 and 80 mya
This may not seem very accurate, but compared to the 4,500 million years the earth has been around it gives us a lot more information than we had before

What can we learn from this?
 Absolute Dating
 Helps us determine the age of the earth
 Helps us determine when specific events in the history of the earth happened (ex. Extinction of the dinosaurs)
 Relative Dating
 Can help us estimate the time span between major earthquakes, storms, tsunamis etc
 Can help us determine the order that life forms developed on earth