1. Unit 7: Geologic History Earth Science- Ms. Gill Note Packet #8
UNIT 7: EARTH’S HISTORY

PACKET 8: EARLY EARTH, SEQUENCING EVENTS,
RELATIVE AGE, ABSOLUTE AGE, FOSSIL RECORD
“Maybe one day I’ll
make a good index
fossil” P.S. I’m
Boris
HONORS EARTH SCIENCE
MS. GILL
NOTE PACKET #8
NAME:_______________________ PER:____ DATE:______
________
Page # ____

2. Unit 7: Geologic History Earth Science- Ms. Gill Note Packet #8
Vocabulary:
absolute dating
Big Bang
correlation
cross-cutting relationships
erosion
evolution
extinction
extrusion
faulting
folding,
fossil record
half-life
index fossil
inclusion
intrusion
isotope
meteoritic debris
original horizontality
Out-gassing
radioactive decay
red-shift (Doppler effect)
relative dating
rock record
stratigraphy
superposition
unconformity
Uniformitarianism
volcanic ash layer
Page # ____

3. Unit 7: Geologic History Earth Science- Ms. Gill Note Packet #8
Earth’s Formation
•Earth formed through the gravitational _________________ and __________________ of asteroids and
rocky debris.
•This accretion of material generated a tremendous ______________ causing the planet to be molten.
•The denser materials settled into the interior and the Earth’s _____________ internal structure formed.
-Earth's first atmosphere 4.6 billion years ago was most likely comprised of hydrogen and helium (two most
abundant gases found in the universe!)Through the process of outgassing, the outpouring of gases from the
earth's interior, many other gases were injected into the atmosphere. These include:
water vapor (produced rain - rivers, lakes, oceans), carbon dioxide, nitrogen
As outgassing occurred over a period of millions of years, the atmosphere evolved to its current state
Life and Evolution:
Variations in Fossils and Environments
•Evidence from the ______________________ (preserved in sedimentary rocks) shows that a wide variety
of life forms have lived in Earth’s changing environments over time.
•The comparisons of fossil remains and ______________________________ enable scientists to make
predictions about the Earth’s past environment.
•A major reason for changes in Earth’s _________________ over geologic time has been the movements of
plates and their associated landmasses.
Fossils and the Evolution of Life
The theory of ______________________ states that life forms change through time.
As environmental conditions change, variations within a species give certain individuals a greater chance for
_________________ and __________________.
Rates of Evolution
The ________________________ provides evidence for the theory of organic evolution.
This also shows that evolution does not always occur at the same _________.
There are times of rapid ___________ and subsequently rapid ________________ of new species.
• An impact event, such as the collision of a comet or asteroid with Earth, may cause catastrophic
environmental changes leading to rapid extinctions and evolutions.
• Such an event probable occurred at 65 million years ago and is associated with a massive extinction of
roughly 70% of the Earth’s species.
Page # ____

4. Unit 7: Geologic History Earth Science- Ms. Gill Note Packet #8
Life On Earth
Precambrian (4.6 - 4.06 b.y.) {Little to No Life}
- Simple organisms (soft-bodied; “jellyfish”)
- Fossils are rare
Paleozoic (540 – 245 m.y.) {Life in the Oceans}
- Organisms proliferate and become more complex (_______________________)
- Shelled (mineralized skeletons and shells) organisms develop (Brachiopods/Trilobites)
- _______________________ develop from lobe-finned fish
- Era ends with a ________________________ killing off more than 95% of the life on earth
Mesozoic Life (245-65) {Life on Land and Oceans, Dinosaurs!}
- “Age of _________________” (dinosaurs, flying reptiles and birds develop)
- Modern _____________________________ begins to develop on land
- Era ends with a mass extinction killing off dinosaurs, ammonoids, flying reptiles, and some
swimming reptiles.
Cenozoic Life (65 m.y. – present) {Life on Land and Oceans}
- “Age of Mammals” (____________ begin to develop and evolve)
- Humans develop from _______________ (Homo Habilus 1.6 m.y.)
How old is the Earth?
Scientists have determined the age of the
Earth to be about 4.6 x 109 (billion) years
old.
4,600, 000, 000 years = 4.6 x 109
years (scientific notations you should
know)
109 = ______________
106 = ______________
103 = ______________
1012 = _______________
The study of Geologic History began in
the late 1700’s when James Hutton
published his Theory of the Earth. In
this work he was the first scientist to
argue effectively that geologic
processes proceed over long spans of
time
Page # ____

5. Unit 7: Geologic History Earth Science- Ms. Gill Note Packet #8
THE PRINCIPLE OF UNIFORMITY:
Geologists can infer events of the past by
________________________________________________________________________________
Uniformitarianism (Principle of _____________________________) :
states that the forces that acted upon the ______________________ crust in the__________________ are
the same as those that are ________________________ today.
****_______________________________________________________________****
Principle of Uniformitarianism
the physical, chemical, and biological processes that operate today have also operated in the geologic past;
“The present is the key to the past”
Relative Dating Techniques:
Relative Dating: determining the age of a rock or fossil relative to the age of surrounding rocks and earth
materials
Relative Dating Laws
-Original Horizontality - states that sediments are deposited in horizontal layers
-Law of Superposition - states that in an undeformed sequence of strata, each bed is older than the one above it
and younger than the one below it.
-Principle of Cross-Cutting Relationships
Intrusions are younger than the rocks than the rocks that they intrude
Extrusions are younger than the rocks they form above.
Faults are younger than the rocks that they cut through
Relative Dating Techniques: Five Basic Laws!
1. Law of ___________________________________________________________________
2. Law of ___________________________________________________________________
3. Law of ___________________________________________________________________
4. Law of ___________________________________________________________________
5. Law of ___________________________________________________________________
Page # ____

6. Unit 7: Geologic History Earth Science- Ms. Gill Note Packet #8
1. Law of Original Horizontality:
_______________________________________________________________________________
_______________________________________________________________________________
If strata are _______________ then they must have suffered some kind of disturbance after they
were deposited.
2. Law of Superposition- the principle that the _______________
layers in a sequence of rock strata must have been deposited
_________________ the layers above, unless the rock strata have
been ___________ or _____________. The __________rocks are
found at the bottom. Geologists can date the ____________ ages of
the strata from __________ to ___________ .
3. Law of Inclusions: A rock must first exist in order to be weathered, deposited and cemented as a
___________ in another rock. Therefore, If rock is composed of _________, the rock fragments must
be _____________ than the rock in which they are found.
Rock fragments (or inclusions)
that are contained in another
rock are older than the rocks in
which they are found
_______ is older in A. _______ is older in B.
The law of inclusions also applies to fossil preserved in bedrock. _____________________ are any
naturally preserved remains or impressions of living things. They are found in
___________________________________, because____________________________________
______________________________________________________________________________
Fossils give us information about _______________________________________.
Unconformity
Buried erosional surfaces that are preserved in the rock record
Create “gaps” in the geologic rock record
Page # ____

7. Unit 7: Geologic History Earth Science- Ms. Gill Note Packet #8
4. Law of Cross-Cutting Relationships: Any ___________ or ____________ must be younger than ALL
the rock through which it cuts. Simply put, the body of rock that is cross-cut had to be there first in
order to be cut by an intruding igneous body or fault.
In general rock is always ____________________ than the process that changed it.
Some processes include: _______________________, ____________________,
___________________, _________________________ & _______________________.
These changes can lead to exceptions to the Law of Superposition:
a. __________________________ is an igneous rock that formed from lava on the surface of the
crust. An _____________________ must be younger than the strata below it, but
_________________ than any layers above.
b. _____________________ are created when molten rock ( ____________) is injected into older
rock layers in the crust. ___________ are ____________ than all the rock layers in contact with them.
c. ___________________ are bends in rock strata.
_____________________ can overturn rock strata so that
______________ rock lies on top of _____________rock.
Explain how folding can create an exception to the Law of
Superposition. _____________________________
________________________________________
d. _________________ are cracks in rock strata.
_______________ produce offset layers. Which
numbers are older than the fault labeled B? _______
Which are younger?__________
Processes that can change the order of rock strata:
Rock strata must be _________________ than the process that changed it.
_________________, _______________ and __________________ __________________
are features created after rock or sediment has been deposited.
Page # ____

8. Unit 7: Geologic History Earth Science- Ms. Gill Note Packet #8
5. Law of Original Lateral Continuity:
When sediment is dumped by an agent of erosion, strata
extends from the source of deposition until it gradually
thins to zero, or until it reaches the edges of the basin
of ____________________. This concept enables
geologists to correlate outcrops of strata that has been
dissected by processes of ______________.
Practice Activities
Directions: List the age rock layers in correct age order from oldest to youngest.
_____________ Oldest
_____________
_____________
_____________
_____________
_____________
_____________ Youngest
_____________ Oldest
_____________
_____________
_____________
_____________
_____________
_____________
_____________
_____________ Youngest
Page # ____

9. Unit 7: Geologic History Earth Science- Ms. Gill Note Packet #8
CORRELATION OF ROCK STRATA:
A. Correlation is ______________________________________________________________
_______________________________________________________________________________
Rock Correlation
• Correlation is the process of matching rock units or events in separate rock formations
• Correlation of rock units and geologic events can be based upon continuity, similar rock composition,
fossil evidence, and volcanic markers.
B. WAYS TO CORRELATE ROCK FORMATIONS:
1. “Walking the outcrop” is done by ______________________________________________
This is correlation by _____________________________________. Similarities in rock texture and
composition can be used to match rock units over large areas
2. You can match the rock strata in one location with the rock strata in more distant locations by
________________________________________________. Fossils can be used to help match
separated rock layers.
3. Time correlation compares ______________ ________________ contained in rock the strata.
4. The best index fossils:
a. ______________________________________________________
b. ______________________________________________________
This ensures that the fossils will have a wide horizontal and narrow vertical distribution
5. Another way of correlating layers by time is through ________________________________.
Violent volcanic eruptions can emit large quantities of volcanic ash. The ash can spread out over a large
area of land creating an excellent geologic marker for rock correlation. These ash falls are very
__________________ events. A single layer of ________________ can be found over a large area,
this allows geologists to make a ________________________ from one location to another at the
position of a common ash fall.
Page # ____

10. Unit 7: Geologic History Earth Science- Ms. Gill Note Packet #8
GEOLOGIC TIME SCALE:
Geologists noticed that rock __________________________ could be identified by the fossils they
contained. They also found that certain _____________________ were consistently located
_____________________ or ______________________ other formations.
From these observations they established a __________________ ____________ ___________
With a sequence of fossil groups from _____________ to ______________each of these groups was
named for a location where its __________________________ could be observed in the rocks.
Example:___________________________
Further observations from around the world established a
_________________ ________________ __________________
based on _______________________________________________
AND _________________________ex:________________&______________
An _________________________ is the process of mountain building.
SEE PAGES 8 & 9 IN YOUR ESRT!!!
GEOLOGIC EVENTS OF THE PAST:
A. _________________________ causes gaps in the geologic record.
B. When a new layer of rock is laid down on a surface that has been____________________,
it forms a buried erosion surface called an __________________________________.
C. How an unconformity forms:
Page # ____

11. Unit 7: Geologic History Earth Science- Ms. Gill Note Packet #8
Absolute Dating:
-Process of determining the exact age of a rock, fossil or Earth material in years before the present
(as opposed to relative ages).
Common units are:
millions of years ago = m.y.a = 106
billions of years ago = b.y.a = 109
-What were some of the techniques used to determine absolute time prior to the discovery of
radioactivity? __________________________ and _______________________
-Modern science now uses radioactive isotopes to find the absolute ages of a given material (rock, fossil,
etc.).
-___________________________ – Instrument used in the detection and study of isotopes
RADIOACTIVE DATING:
A. Fossils enabled geologists to give __________________________ time. Relative time compares
rock ages to _________________. Example: The limestone is older than the sandstone.
B. Measurements of natural _________________________ in rocks have allowed
_________________ time scale to be an __________________ time scale.
The ________________ _______________ of an object is measured in years.
Example: The limestone was formed 2 mya (million years ago) and the sandstone was formed 1 mya.
Let’s review some basic chemistry to see how this works…
Radioactive Isotope Dating
• An element is a substance consisting of atoms that are chemically alike.
• Most elements exist in several different types of isotopes (atoms with a different number of
neutrons in their nuclei).
• The nucleus (containing neutrons and protons) of radioactive isotopes is unstable and over time
they will emit particles and electromagnetic energy. This is known as Radioactive Decay,
and changes the radioactive isotope into other isotopes or atoms. This occurs until,
eventually a stable isotope forms.
Page # ____

12. Unit 7: Geologic History Earth Science- Ms. Gill Note Packet #8
How can we use radioactive elements to date things?
The rate of decay (breakdown) for any radioactive isotope is ______________.
Over a given period of time, a definite fraction of the atoms of an isotope will ____________
ISOTOPE: ______________________________________________________________
_____________________________________________________________
Ex. C C
D. If the nucleus has more or fewer than the normal number of _________________, The isotope may
be _______________________________.
E. Radioactive isotope will break down naturally into a lighter element called __________________
__________________ which is stable.
*This process is called __________________________ _____________.
RADIOACTIVE DECAY: When an unstable ______________ element changes into a completely
different (but stable) ___________ element.
F. A sample starts out at “Time Zero” with ________ percent of radioactive material.
( Time Zero: when the sample originally formed by cooling and solidification)
As time goes by and the sample gets older, the radioactive elements decay, and ____________
radioactive atoms remain in the sample. Therefore, the higher the ratio of decay product to radioactive
element the _______________ the sample. The ratio between the mass of the radioactive element and
it’s decay product in a sample is called the ________________________
G. The decay of the parent atoms in a sample to daughter atoms is a _________ process. That happens
at _____________ rates for different radioactive elements. Lets model this with pennies.
H. The rate of decay of a radioactive element is measured by it’s ________ _______
HALF-LIFE: ______________________________________________________________
_____________________________________________________________________
Half Lives of Radioactive Isotopes
• The rate of decay for any radioactive isotope is constant.
• Over a given period of time, a definite fraction of the atoms in an isotope will decay to a
stable form.
• The time required for half of the atoms in a given mass of an isotope to decay is known as the
half-life of the isotope.
• Each radioactive isotope has it’s own characteristic half-lfe, which is not affected by any
environmental conditions, mass or volume.
• The front page of the ESRT lists the radioactive isotopes, and information regarding their
decay and half-life.
Page # ____

13. Unit 7: Geologic History Earth Science- Ms. Gill Note Packet #8
Complete the Chart using the front cover of the Reference Tables:
RADIOACTIVE ELEMENT DECAY PRODUCT HALF-LIFE
1 Carbon-14
2 Potassium-40
3 Uranium-238
4 Rubidium-87
Selecting the Best Radioactive Element:
AGE OF SAMPLE RADIOACTIVE ELEMENT
1 Under 50,000 (RECENT)
2 Over 50,000 (OLDER)
Carbon-14 is used for dating:
_______________________________________ & _____________________________________
“Time Zero” for carbon dating begins when the organism ______________ or when the _________ burns
out.
• Radioactive isotopes with very long half-lives are excellent for dating very old rocks, but for
younger objects, isotopes with shorter half-lives present a better tool to find accurate absolute
ages.
• One such isotope is Carbon-14 , with a half-life of 5,700 years.
• C-14 dating – also called radiocarbon – can be used to date rocks and more importantly organic
remains up to approximately 70,000 yrs.
• This method has been used to date early humans, mastodonts, and many other geologically recent
organic remains.
Can all rocks be dated using this technique?
-Igneous and Metamorphic rocks work excellent for radioactive dating because at the time of
crystallization (or recrystallization), a specific ratio of stable and radioactive isotopes are incorporated into
the crystals.
-On the other hand, sedimentary (clastic) rocks do not work well because they are composed of older, pre-
existing rock fragments.
Page # ____

14. Unit 7: Geologic History Earth Science- Ms. Gill Note Packet #8
Calculating the age of a rock: The ratio between the amount of the original isotope (parent) and the
amount of its decaying product (daughter), is used to establish the absolute age of a sample.
1. What would be the age of the rock that has equal amounts of
C-14 and its decay product N-14?
2. What % of the sample is radioactive after the following half-lives,
After 1 half-life:
After 2 half-lives:
After 3 half-lives:
3. After 11,200 years how much C-14 would remain in a 10 gram sample?
Page # ____