Geologic
Time
Notes
Geologic
Time
Notes
Fossils can only
be found in
rocks.
Fossils can only
be found in
rocks.
sedimentary
Why is this statement fals
e: “The caveman had dino
saur for breakfast.”?
Why is this statement fals
e: “The caveman had dino
saur for breakfast.”?
man and dinosaurs
never lived at the same time
man and dinosaurs
Geologic Time Scale
Geologic
Time Scale
The geologic Time Scale is a record of Earth’s history
The Earth is 4.6 Billion Years Old
The names of the divisions do not change however the years designating the
beginning and end of these divisions are often reconsidered
The geologic Time Scale is a record of Earth’s history
The Earth is 4.6 Billion Years Old
The names of the divisions do not change however the years designating the
Eons
Eons
The time scale is divided into eons
An Eon is the longest time unit and is measured in billions of years
The time scale is divided into eons
Eons
Eons
The history of the Earth is divided
into 4 eons:
Hadeon(4.6 Bya-3.8 Bya)
Archaen(3.8 Bya-2.5 Bya)
Proterozoic(2.5 Bya-542 mya)
Phanerozoic(542 mya-Present)
The history of the Earth is divided
into 4 eons:
Hadeon(4.6 Bya-3.8 Bya)
Archaen(3.8 Bya-2.5 Bya)
Precambrian
Precambrian
The Precambrian includes the
Hadeon Archaen
Proterozoic eons.
Includes 90% of Earth’s History
The end of the Proterozoic is defined by the first appearance of organisms with hard
parts(shells, skeletons)
The Precambrian includes the Hadeon
Archaen
Proterozoic eons.
Includes 90% of Earth’s History
The end of the Proterozoic is defined by the first appearance of organisms with hard
Precambrian
Precambrian
Up until the end of the Proterozoic all organisms had soft bodies
Many of these organisms resemble:
Sponges Snails Worms
Up until the end of the Proterozoic all organisms had soft bodies
Many of these organisms resemble:
Eras
Eras
Eras are the next longest span of time.
Eras are measured in hundreds of millions of years
Eras are the next longest span of time.
Eras
Eras
The names of the eras of the Phanerozoic are based on their age
“Paleo” means old
“Meso” means middle “Ceno” means recent “Zoic” means life
The names of the eras of the Phanerozoic are based on their age
“Paleo” means old
Eras
Eras
The Phanerozoic Eon is divided into 3 Eras:
Paleozoic(542 mya-250 mya) Mesozoic(250 mya-65 mya) Cenozoic(65 mya-Present)
The Phanerozoic Eon is divided into 3 Eras:
Paleozoic Era
Paleozoic Era
During the Paleozoic era the oceans had a wide diversity of plants and animals
Trilobites were the dominant organism in the oceans during the early Paleozoic
All trilobites were extinct by the end of the Paleozoic
During the Paleozoic era the oceans had a wide diversity of plants and animals
Trilobites were the dominant organism in the oceans during the early Paleozoic
Paleozoic Era
Paleozoic Era
Paleozoic Era
Paleozoic Era
Land plants and land animals first
Land plants and land animals first
appeared
appeared
At the end of the Paleozoic 90% of
At the end of the Paleozoic 90% of
marine organisms went extinct
marine organisms went extinct
This is considered to be the largest mass
This is considered to be the largest mass
extinction event in Earth’s History
extinction event in Earth’s History
Land plants and land animals first
Land plants and land animals first
appeared
appeared
At the end of the Paleozoic 90% of
At the end of the Paleozoic 90% of
marine organisms went extinct
marine organisms went extinct
This is considered to be the largest mass
This is considered to be the largest mass
extinction event in Earth’s History
Mesozoic Era
Mesozoic Era
The Mesozoic era is known for:
The emergence of the dinosaurs Reef Building corals
Predatory reptiles
Amphibians living on land and in water
Dinosaur population began to decline towards the end and mammals began to evolve
The Mesozoic era is known for:
The emergence of the dinosaurs Reef Building corals
Predatory reptiles
Amphibians living on land and in water
Mesozoic Era
Mesozoic Era
Like the Paleozoic the end of the Mesozoic is marked by a massive extinction event
Cenozoic Era
Cenozoic Era
During the Cenozoic:
Mammals increased in number and diversity
Human ancestors developed
Grasses and flowering plants expanded on land
Ocean life remained relatively unchanged however
During the Cenozoic:
Mammals increased in number and diversity
Human ancestors developed
Grasses and flowering plants expanded on land
Periods
Periods
Eras are divided into periods
Periods are usually defined by life forms that appeared or went extinct during that time
Some periods are named for a
geographic area in which the first rock of that age was discovered
Eras are divided into periods
Periods are usually defined by life forms that appeared or went extinct during that time
Some periods are named for a
Periods
Periods
The Mississippian period was named for a distinctive limestone that formed along the Mississippi River
Periods
Periods
Periods
Periods
The Jurassic Period is named for the
The Jurassic Period is named for the
rocks discovered in the Jura Mountains
rocks discovered in the Jura Mountains
in Europe
in Europe
The Jurassic Period is named for the The Jurassic Period is named for the
rocks discovered in the Jura Mountains rocks discovered in the Jura Mountains
Epochs
Epochs
Periods are divided into Epochs which are measured in millions of years to tens of
millions of years
The fossil record the Cenozoic Era is relatively complete
There has been less time for weathering and erosion to destroy the fossil record
Periods are divided into Epochs which are measured in millions of years to tens of
millions of years
The fossil record the Cenozoic Era is relatively complete
Epochs
Epochs
Certain organisms are used to distinguish the various epochs
Marine Fossils are used to mark the Oligocene Terrestrial plant fossils are used to mark the Eocene
Certain organisms are used to distinguish the various epochs
Relative Dating Of Rocks
Relative Dating Of Rocks
Relative Dating estimates the order of past geologic events by using basic stratigraphic rules
Relative dating does not give us the ages of past events but can tell us the order in
which they happened
Relative Dating estimates the order of past geologic events by using basic stratigraphic rules
Relative dating does not give us the ages of past events but can tell us the order in
Relative Dating
Relative Dating
Uniformitarianism states that “The Present is the Key to the past”.
In other words processes that are occurring today were more than likely occurring
throughout Earth’s history
Uniformitarianism states that “The Present is the Key to the past”.
In other words processes that are occurring today were more than likely occurring
Relative Age
Relative Age
If a sedimentary rock
outcrop has not been
overturned, which layer
would be the oldest? What
is this principle known as?
If a sedimentary rock
outcrop has not been
overturned, which layer
Principle of
Superposition
Principle of
Superposition
oldest rock layers
are on bottom
Principle of Superposition
Principle of Superposition
The principle of superposition states that in an undisturbed rock sequence the oldest
rocks are on the bottom and going up they progressively get younger
The principle of superposition states that in an undisturbed rock sequence the oldest
Using this principle, label
the strata below from
oldest to youngest.
Using this principle, label
the strata below from
Faults are always
(older, younger)
than the rocks they cut
through.
Faults are always
(older, younger)
Which is older:
F or S
If a geologist finds an
igneous sill, how can she
determine if the sill is an intrusion
or an extrusion?
If a geologist finds an
igneous sill
, how can she
Intrusions
Intrusions
extrusions
extrusions
Is “H” an intrusion or
extrusion?
How can you tell?
Is “H” an intrusion or
extrusion?
H is an intrusion.
Contact
metamorphism
on top
H is an intrusion.
Contact
What is an
unconformity?
What is an
unconformity?
a buried erosional surface
a buried erosional surface
a part of the rock record is missing
a part of the rock record is missing
How does it complicate
the relative dating of
rock layers?
How does it complicate
the relative dating of
What processes could
lead to an unconformity?
What processes could
lead to an unconformity?
weathering and erosion
What characteristics must
fossils have in order to be
good index fossils?
What characteristics must
fossils have in order to be
good index fossils?
lived over a large geographic area (large
horizontal distribution)
lived for a short period of time (small
vertical distribution)
lived over a large geographic area (large
horizontal distribution)
I n the diagram below, a geologist has matched up rock layers based on index fossils.
I n the diagram below, a geologist has matched up rock layers based on index fossils.
In geology, this is referred
to as CORRELATION
Why are radioactive isotopes useful in determining the absolute age of a rock?
What can be done to change the half-life of a radioactive isotope?
Why is this important?
Absolute Dating
Techniques
Absolute Dating
Techniques
Absolute dating allows scientists to
determine the actual age of a rock, fossil or other object
Scientists use radioactive decay to determine the ages of rocks
Absolute dating allows scientists to
determine the actual age of a rock, fossil or other object
Radioactive Decay
Radioactive Decay
Radioactive substances emit particles at a set rate
As they emit particles the number of protons and neutrons change and the element is
converted into a different element
Radioactive dating is the emission of
radioactive particles and the resulting change into other elements
Radioactive substances emit particles at a set rate
As they emit particles the number of protons and neutrons change and the element is
converted into a different element
Radioactive dating is the emission of
Radiometric Dating
Radiometric Dating
Radiometric dating is the process in which scientists determine the ratio of parent
nuclei to daughter nuclei
After they determine the ratio of parent to daughter nuclei they can figure out the
actual age of the object
Radiometric dating is the process in which scientists determine the ratio of parent
nuclei to daughter nuclei
After they determine the ratio of parent to daughter nuclei they can figure out the
Radiometric dating
Radiometric dating
As this process takes place the “Parent” decays into the “daughter”
The parent isotope is what the element originally was
The daughter isotope is what the parent isotope is turning into
As this process takes place the “Parent” decays into the “daughter”
The parent isotope is what the element originally was
Radiometric Dating
Radiometric Dating
Example:
Uranium-238 will decay into Lead-206 during a specific span of time
The rate at which these particles decay remains constant making them good
indicators of the actual age of the object
Example:
Uranium-238 will decay into Lead-206 during a specific span of time
The rate at which these particles decay remains constant making them good
Half Life
Half Life
Half life-The period of time it takes for one half of the isotope to decay
Useful Isotopes
Useful Isotopes
Radioactive Isotope (Parent)
Approximate Half Life Decay Product (Daughter)
Rubidium-87 48.6 Billion Years Strontium-87
Thorium-232 14 Billion Years Lead 208
Potassium 40 1.3 Billion Years Argon 40
Uranium 238 4.5 Billion Years Lead 206
Uranium 235 700 Million Years Lead 207
Useful Isotopes
Useful Isotopes
Carbon 14-Useful for finding the age of materials that are of organic origin
Amber
Humanoid Bones Papyrus
Charcoal Fragments
The half life of Carbon 14 is 5730 therefore it would be used to date rocks that are
thousands of years old
Carbon 14-Useful for finding the age of materials that are of organic origin
Amber
Humanoid Bones Papyrus
Charcoal Fragments
The half life of Carbon 14 is 5730 therefore it would be used to date rocks that are
Half Lives
Half Lives
Number Of Half Lives Percent Parent Isotope Percent Daughter Isotope Elapsed Years0 100% 0% 0
1 50% 50% 5730
2 25% 75% 11560 (5730 X 2)
3 12.5% 87.5% 17090
Half Lives
Half Lives
The half life of U-238 is 4.5 Billion Years old so therefore it would not be useful to date something that is thousands of years old
The isotope used is based on the age range of the rock
The half life of U-238 is 4.5 Billion Years old so therefore it would not be useful to date something that is thousands of years old
What radioactive isotope could be used to determine the absolute
age of material that was recently living?
carbon-14
What radioactive isotope could be used to determine the absolute
age of material that was recently living?
If there is a 100g sample of C14, how many grams of
C14 would remain after three half-lives?
How long would this take? Show all work.
100g 50g 25g 12.5g
3 half-lives x (5.7 x 103) =1.71 x 104
Practice
Practice
How old are the following rocks:
Contains 50% U-235, 50% Pb-207 Contains 25% K-40, 75% Ar-40 Contains 12.5% C-14, 87.5% N-14 Contains 50% U-238, 50% Pb-206
How old are the following rocks:
Other Absolute Dating
Techniques
Other Absolute Dating
Techniques
Dendrochronology-The science of
comparing annual growth rings in trees to date event and changes in the past
environments
During the spring a tree experiences it’s greatest growth
During the winter it’s growth is less
Dendrochronology-The science of
comparing annual growth rings in trees to date event and changes in the past
environments
During the spring a tree experiences it’s greatest growth
Dendrochronology
Dendrochronology
The widths of a trees rings are related to the climate conditions during growth
periods
The widths of a trees rings are related to the climate conditions during growth
Varves
Varves
Vares are bands of
alternating light and dark colored sediments of sand, clay and silt
During the Pleistocene (11,000 years ago) there
was mass glaciation
When the glaciers melted the glacial sediments were deposited in lakes
Vares are bands of
alternating light and dark colored sediments of sand, clay and silt
During the Pleistocene (11,000 years ago) there
was mass glaciation
Varves
Varves
The glacier sediment is dark in color When they mix with sediments that
accumulated during warm temperatures varves are formed
The glacier sediment is dark in color When they mix with sediments that
Key Beds
Key Beds
Key Beds-Sediment layers that serves as a time marker in the rock record.
Key beds result from:
Volcanic Ash
Meteorite Impact debris
Found in rocks deposited during the Cretaceous Period
Key Beds-Sediment layers that serves as a time marker in the rock record.
Key beds result from:
Volcanic Ash
Meteorite Impact debris
Key Beds
Key Beds
Key Beds are released by volcanic eruptions as well
Will be used to date rocks back to the eruption of Mount St. Helens(1980)
Key Beds are released by volcanic eruptions as well
Evolution
Evolution
Explain the theory of evolution.
Explain the theory of evolution.
organisms adapt to their environment in order to survive
Evolution
Evolution
Explain how the fossil record supports this theory
Explain how the fossil record supports this theory
can see that different organisms have changed over time
