Transcript File - Carlson Connection

Geologic Time
Relative Dating
Any method of determining whether an event or
object is older or younger than the events or
objects around it.
The word relative means “compared to.”
How old is a rock layer compared to the rock
layers around it?
Relative Dating
Scientists all over the world send in information about the
rock layers in their area, these are analyzed and compared
to the “geologic column”
The geologic column is an ideal sequence of rock layers
that contains all the known fossils and rock formations on
earth.
By comparing a sample to the geologic column, you can
find it’s relative age and also whether some events or layers
are missing.
The Geologic Column
Relative Dating
In rock layers, we obey the rule of superposition which
says...
Younger over older.
This means that the oldest rocks in an area are the deepest
underground and the youngest are near the surface unless
there has been a disturbance.
A Geologic Sandwich
In this assignment, you will use the small sandwiches on the
menu of a sandwich shop to determine the order of the
ingredients in a giant sandwich that the shop offers.
The small sandwiches are like the samples of rock layers
from all over the world and the giant sandwich is like the
geologic column.
Let’s take a look at the menu!
A Geologic Sandwich
This is the order of ingredients on
the giant sandwich from the
geology rock cafe! How did you
do?
A Geologic Sandwich
Superposition
The principle that older layers are on the bottom and
younger layers are on the top, if there has not been a
disturbance
Remember: younger over older
Scientists know that rock layers are undisturbed when they
are horizontal.
Possible Disturbances
Fault
Folding
Intrusion
Tilting
Unconformity
Fault
A breaking and sliding of rock
layers.
A break in the Earth’s crust
A fault is younger than the
layers it has broken.
Fold
A Occurs when two plates
slide towards each other.
Rocks that are deeper fold
instead of breaking.
This is how mountains are
made
Intrusion
When a lava flow interrupts
rock layers.
An intrusion is younger than
the layers it disturbs.
Unconformities
A place in the rock record where layers are missing
A gap in geological history
Layers of rock have been deformed, weathered, or eroded
away
Erosion is a major cause of unconformities
Usually indicated by a wavy line in a rock layer diagram
Hints:
A cross-cutting feature is always younger that the layers it
cuts across. This is because a layer must exist BEFORE it
can be disturbed.
Tilting is the slanting of rock layers
Find the Disruptions
Find the Disruptions
Find the Disruptions
Find the Disruptions
Find the Disruptions
Divisions of Geologic Time
Age of the Earth: 4.6 billion years
Earth’s History is divided into sections.
The largest chunk of time is called an Eon
Eons are divided into smaller parts called Eras
Eras are divided into Periods
Some Periods are divided into Epochs
Why Epochs?
As we study the past that is closest to us, we get more
information than we can about the distant past
Information from the distant past may have been destroyed
or be too far below the Earth’s surface to access.
Our Place on the Scale
Eon: Phanerzoic
Era: Cenozoic
Period: Quaternary
Epoch: Holocene
Important Events in History
4,600 mya - Planets formed
4,200 mya - oldest thing on Earth (Zircon Crystal)
3,500 mya - first life forms (single celled)
2,500 mya - Oxygen in the Atmosphere
800 mya - multicellular life
400 mya - life moves to land
248 mya - dinosaurs show up
Important Events in History
65 mya - dinosaurs go extinct (probably because of climate
change) - they were around for a total of 83 my
6 mya - humanoid life forms (walked upright)
2 mya - Ice Age
100,000 years ago - first appearance of species Homo
sapiens (That’s us)
Geologic Time Scale
Geologic Time Scale
Geologic Time Scale