Download Geologic Time

WARM-UP
• Define the following terms in
your notebook (use the textbook):
1. Index fossil
2. Mold
3. Superposition
4. Cast
5. Unconformity
6. Correlation
7. Cross-cutting relationships
8. Principle of original horizontality
9. Uniformitarianism
Geologic
Time
A life time ago!!!
• The average man lives for roughly
67 years.
– During this time they grow up, go
to school, get jobs, get married,
have kids, and then die
• The Earth was formed
approximately 4.5 billion years
ago and A LOT has happened
since then
The Break Down
The history of the Earth is broken
into different parts
– Eon- the longest length of time
– Era
– Period
– Epoch- the shortest length of
time
Uniformitarianism
• States that the natural processes
operating in the past are the
same as those that can be
observed operating in the
present.
“The Present is the Key to the
Past!”
• Early geologists noticed that
certain things (plants and
animals) disappear completely
or just appear in the rock record.
• Until recently there was no way
to tell just how old a rock unit
actually was so we use relative
dating
Relative Dating
• Relative dating tells scientists if a
rock layer is “older” or “younger”
than the other by using basic
laws/rules, observing where fossil
organisms lay in bands of rocks
throughout the world
** DOES NOT GIVE
ACTUAL DATE **
Which came first?
a) My mother's birth
b) My maternal grandmother
meets my maternal grandfather
c) My father meets my mother
d) My birth
e) I graduate from high school
f) My maternal grandmother's
birth
Law of Superposition
• States that in an undisturbed
horizontal bed of sedimentary
rocks, the oldest rock will be on
the bottom with the younger
rock on top
Principle of Cross-Cutting
Relationships
• States that a feature that cuts
or penetrates another rock
body is younger than the one
being cut.
Which came
first?
Which came
last?
Index Fossils
**Key to the Relative Time Scale**
• Forms of life which existed
during limited periods of geologic
time and thus are used as guides
to the age of the rocks in which
they are preserved.
Layers occurred at the same point
in time
Radiometric Dating
• A technique used to date
materials by looking at the
observed abundance of a
naturally occurring radioactive
isotope and its decay products,
using known decay rates (such as
uranium, strontium, and
potassium)
• Often called Radioactive Dating
QUESTIONS????
Assignments
• Class work
–In groups of four, complete the
Problem Solving Lab p. 560 #1-6.
Write the question and the answer
• Homework
–Individually, complete the
Chapter Assessment p. 561 #1-5.
Write the question and the answer