Transcript Geologic History

Geologic History
Quickwrite:
In 2-3 sentences answer one of the
questions below:
• How do you think scientists know which
fossils are older and which fossils are
younger?
• What do you think causes mass
extinctions?
Topic: Relative Dating
Objectives: Day 1 of 3
• To learn how scientists use relative dating
techniques to put geologic events in order
• To learn how to apply the laws of geology
(the law horizontality, law of superposition, law
of cross-cutting relationships) to relative
dating
Relative Dating
• The concept of dating rocks by putting geologic
events in order
• It does not give an exact age of rocks
8.
7.
3.
2.
1.
5. Magma Intrusion
Relative Dating
• The concept of dating rocks by putting geologic
events in order
• It does not give an exact age of rocks
8.
7.
3.
2.
1.
4. Magma Intrusion
What is Relative Dating?
• The concept of dating rocks by putting
geologic events in_______
Answer Bank
Younger
gap
Top
after
Bottom
Order
flat
8.
7.
3.
2.
1.
4. Magma Intrusion
Law of Superposition
• In layers of deposited sedimentary rock,
the oldest rock layers are at the bottom
and the rock layers become younger
toward the top
3.
2.
1.
Law of Superposition
• Principle of Superposition: States that the
oldest rock layers are at the bottom and
the rock layers become younger toward
the top
The law of Superpostion: Old rocks formed
on the bottom and young rocks are at the top
What is the Law of Superposition?
• In layers of deposited sedimentary rock,
the oldest rock layers are at the ____ and
the rock layers become younger toward
the ____
3.
2.
1.
Answer
Bank
Younger
gap
Top
after
Bottom
Order
flat
Law of Horizontality
Law of Horizontality
Sediments are originally deposited in flat horizontal layers. If
the rocks are folded or are laying at a steep angle, they must
have been disturbed or tilted after they were originally
deposited.
What is the Law of
Horizontality?
Sediments are originally deposited in ____ horizontal
layers. If the rocks are folded or at an angle, they must
have been disturbed _____they were originally deposited.
Answer
Bank
Younger
gap
Top
after
Bottom
Order
flat
Unconformities
• Think of layers of rock as pages of a history
book
• If we remove pages, the book is incomplete
• An unconformity is when layers of rock are
missing
3.
2.
1.
3.
1.
Unconformities:
Here’s how it works!!!!
5.
3.
4.
3. Unconformity
2.
1.
(weathering and erosion
create a gap in geologic time
Unconformities
• An unconformity is a gap in rock layers due to
erosion and weathering or a break in the
depositing of sediments (missing rock layers)
3.
2.
1.
3.
1.
What is an Unconformity?
• An unconformity is a ____ in rock
layers due to erosion and weathering
or a break in the depositing of
sediments (missing rock layers)
3.
2.
1.
3.
1.
Answer Bank
Younger
gap
Top
after
Bottom
Order
flat
Law of Cross Cutting Relationships
• The law of cross cutting relationships
states that a fault line or an igneous
intrusion must be younger than the rock it
cuts across.
3.
2.
1.
4. Magma Intrusion
What is the Law of Cross Cutting
Relationships?
• A fault line or an igneous
intrusion must be _____ than
the rock it cuts across.
3.
2.
1.
4. Magma Intrusion
Answer Bank
Younger
gap
Top
after
Bottom
Order
flat
Practice:
Start with the oldest rock and work your way to the youngest
Young
1. H
2. G
3. F
4. E
5. D
6. C
7. B
8. A
Old
H
F
G
C
B
A
D
Magma Intrusion
Summary:
• The law of ______ states that
Sediments are deposited in flat
horizontal layers
• When rock layers are missing in the
geologic record we call it an _______
• The law of ____ ____ relationships
states that A fault line or an igneous
intrusion must be younger than the
rock it cuts across.
Answer Bank
unconformity
horizontality
Cross-cutting
superposition
Quickwrite:
In 2-3 sentences answer one of the
questions below:
• How do you think scientists know the
earth is 4.6 billion years old???
• If you shook up 100 pennies in a box,
how many do you think would be
heads???? How many do you think
would be tails????
Topic: Absolute Dating
Objectives: Day 2 of 3
• To will how scientists use absolute dating
to determine the exact age of rocks
• I will know the concept of half life and
radioactive decay
Absolute Rock Dating
• How do we know the earth is 4.6 billion years
old?
• How do we know when dinosaurs lived?
• Thankfully, we can answer those questions by
using Absolute Dating
• Absolute Dating is a method used by
geologists to determine the age of a rock or
fossil
• By analyzing the properties of atoms in rocks
and fossils we can get a really accurate date
for when the rock or fossil formed
What is Absolute Dating?
• Absolute Dating is a method used
by geologists to determine the
exact _____ of a rock or fossil
• It is different from relative dating
because it gives an exact age
Answer
Bank
Element
Age
determine
decay
Radioactive Decay
• Radioactive Decay: The decay of an atom of
one element to form another element, an
example would be when uranium becomes
lead or carbon 14 becomes Nitrogen
• For Example, after uranium-238 loses two
protons and neutrons it becomes Lead- 206
which is stable and no longer changes
Uranium
Lead
What is Radioactive Decay?
• The decay of an atom of one element
into another _____
Answer
Bank
• ex. uranium becomes lead
Element
Age
determine
decay
Parent and Daughter Material
• In the example of Uranium
and Lead, which one is the
Parent material and which
one is the daughter material?
• Uranium becomes Lead and
is therefore the parent
material
• Lead is the stable daughter
product
Uranium is the
parent material
Lead is the
daughter material
Half-Life
• Half life is the time it takes for half of the
of the parent material to decay
• For example, if I had one pound of
Uranium it would take 4.5 billion years
for half of it to decay
• Therefore, we would only have half of
what we started with after 4.5 billion
years have passed
• How much would we have after another
4.5 billion years have passed?
What is Half life?
• Half life is the time it takes for half of the
of the parent material to _____
• Example: Lead
Answer
Bank
Element
Age
determine
decay
Who thinks they understand half-life?
1) What is the half life of
uranium-238?
2) According to this
diagram, how much
uranium remains after
4.5 Billion years? Lead?
3) After 9 billion years, how
much uranium is left?
Lead?
= parent material
100% Parent Material
= daughter material
½ life = 50,000 yrs
50% Daughter Material
50% Parent Material
Amount of Parent Material
100
75% Daughter Material
25% Parent Material
87.5% Daughter Material
12.5% Parent Material
75
50
25
50,000 yrs
0
1
2
3
Number of Half Lives
4
5
Old vs. Young Rock
• We use Uranium half life to measure the age
of the earth, which is very old
• But, how would we measure something that is
younger, like tree rings or artifacts from an
ancient land?
• Because Carbon-14 ( a radioactive form of
carbon) has a half-life of 5,730 years, we can
use it to date rocks that are much younger
(unlike uranium, which has a half-life of 4.5
billion years)
• After 5,730 years Carbon-14 will decay into
stable Nitrogen
Radiometric Dating
• To a geologist who studies rocks in order
figure out earth’s history, these radioactive
elements that decay are like a clock ticking
away, keeping track of time since that’s
passed since earth formed
• Radiometric Dating: A dating method that
uses the rate of decay of radioactive atoms in
rocks by the amount of parent and daughter
product to determine the absolute age of a
rock
What is Radiometric Dating?
• Dating method that uses the
rate of decay of radioactive
atoms in rocks by the amount
of parent and daughter product
to _____ the absolute age of a
rock
Answer
Bank
Element
Age
determine
decay
Summarize:
• Read the following scenario to complete the
answer below: A piece of coal (made of carbon) from a
cave man’s fire is found to have about 50% Carbon-14
and 50% Nitrogen. The half life of Carbon-14 is 5730
years.
100%
Carbon-14
5,730years
Answer
Bank
Parent
age
Daughter
radiometric
50%
50%
Carbon-14 Nitrogen
• Carbon-14 is the _____ material and Nitrogen
is the _____material
• The caveman’s coal and fire is ______years
old
• Scientist’s use _____dating to determine the
absolute ____of rocks and fossils
Quickwrite:
In 2-3 sentences answer one of the
questions below:
• Where do you think all the oxygen in our
atmosphere came from?
• How long do you think Humans have on this
planet for????
• Considering the age of the earth 4.6 BYO,
When do you think life first appeared??
Topic: Geologic Time
Objectives: Day 3 of 3
• I will know the major geologic events that
have transformed our earth
• I will know the geologic time scale and it’s
major divisions
Geologic Time Scale
• The geological time scale is
the geologic history of the
planet from formation to the
present.
• It is starts with large
divisions of time called
eons and is subdivided into
successively smaller units
such ass eras and period
• The geologic time scale is
based on dominant
lifeforms, and mass
extinction events
Geologic Time Scale
Some of the major time
eras include the:
• Precambrian
Oceans and atmosphere form
• Paleozoic
Invertebrates, plants and fish are the
dominant forms of life
• Mesozoic
Reptiles are the dominant forms of life
• Cenozoic
Mammals are the dominant forms of life
What is the Geologic Time Scale?
• Time scale from the beginning of
earth to present
• It is broken time divisions such
as Eras, & Periods that are
based on the ____record,
dominant life forms, and mass
____events
Answer Bank
Extinction
90%
Meteorites
Explosion
Fossil
Oxygen
Humans
Photosynthesis
Welcome to Earth
4.6 Billion Years ago
4.6 billion years ago
Earth Forms
Steam
Thisslowly
cooled
was
and
planet
was
intolike
clouds,
Our oceans
During
Itwhat
was
formed
theour
acondensed
Precambrian,
harsh
over
environment.
millions
offor
years
These
4As
clouds
billion
years--90%
Released
precipitation
of earth’s
History
(rain)
our
oceans
volcanoes
Meteorites
and released
atmosphere
bombarded
steam
formed
our
earthfor
millions
Scientists
years,
call
this
eventually
period
forming
the Precambrian
our
One
along
ofofthese
And
with
gases
volcanoes
other
was
important
spewed
steam
or
events
out
(H
O)oceans
2gases
Precambrian
CO
CO
2
22
CO
H
HH
O
22O
2O
2N
Another Remember
gas given off
volcanoes
theby
recipe
These phytoplankton
were (CO
very
important
isfor
Carbon
Dioxide
Photosynthesis
is:
2) microscopic
important
event
during
the
AboutAnother
2 billion
years
ago,
primitive
Because
they
helped
create
an
oxygen
COmicroscopic
H2O
 the
Ophytoplankton
+
C
Precambrian
was
appearance
single
celled
forms
life
2+
2 of
6Hcalled
12O6
These
atmosphere
for life
to thrive
in
ofrich
the Oxygen
first
single
celled
forms
of
life
Phytoplankton
began
to
fill
the
oceans
absorbed
As
CO
from
fill
volcanoes
our
atmosphere,
and
through
2
Photosynthesis
Our skies eventually
released
became
Oxygen
Blue
(O2)
into our atmosphere
4.6 billion years ago
Earth Forms
Precambrian
O
O
O222
CO
CO
CO222
How did our atmosphere
become rich in oxygen?
Answer Bank
• Primitive phytoplankton and algae
bacteria called stromatolites released
oxygen into our atmosphere through
_____ about 2 bya
Extinction
90%
Meteorites
Explosion
Fossil
Oxygen
Humans
Photosynthesis
Major Geologic Events of
the Precambrian Era
4.5 bya- Moon forms
3.8 bya- first
oceans form
3.5 bya- 1st single
celled forms of life
1.1bya-1st continent
Rhodinia forms
1.3 bya- first multi
celled forms of life
Precambrian
2 bya- oxygen rich
atmopshere forms
What are major geologic events
of the Precambrian Era?
Answer Bank
•
•
•
•
•
3.8 bya- oceans form
3.5 bya- 1st single celled forms of life
2 bya- ____ rich atmosphere forms
1.3 bya- 1st multi celled forms of life
1.1bya-1st continent Rhodinia forms
Extinction
90%
Meteorites
Explosion
Fossil
Oxygen
Humans
Photosynthesis
Paleozoic Era
The Paleozoic Era witnessed an explosion of life
Very shallow seas covered most of the earth
Through out these shallow seas lived some of the first complex
forms of life Including: invertebrates (shell fish), fish and plants
Some of these animals included trilobites,
ammonites (squid like creatures with shells)
Precambrian
Major Geologic Events of
the Paleozoic Era
Precambrian
Major Geologic Events of
the Paleozoic Era
245 mya- Mass Extinction 90% of all life
322 mya- First reptiles appear
513 mya- First land plants appear
536 mya- 1st fish & invertebrates appear
570 mya- Explosion of life
Precambrian
What are major geologic events
of the Paleozoic Era?
• 570 mya- _____ of life
• 536 mya- 1st fish & invertebrates
513 mya- 1st land plants
• 322 mya- 1st reptiles appear
• 245 mya- Mass Extinction ___%
of all life
Answer Bank
Extinction
90%
Meteorites
Explosion
Fossil
Oxygen
Humans
Photosynthesis
Mesozoic Era
The Mesozoic Era was the age of reptiles
& witnessed the evolution of the largest
animals to have ever walked the earth
The dinosaurs would eventually go extinct
and give rise to modern day birds
Precambrian
Dinosaur Demise
• There is mounting
evidence that a large
meteorite impact
slammed into earth 65
mya ending the
Cenozoic era
• This impact would
have caused
widespread
devastation and fires
Dinosaur Demise
• Ash and smoke
from fires could
have blocked out
enough sunlight
changing the global
climate; decimating
and wiping out the
cold blood reptiles
Major Geologic Events of
the Mesozoic Era
Precambrian
Major Geologic Events of
the Mesozoic Era
65 mya- Mass extinction 60% of all life perishes
160 mya- First Birds appear
180 mya- Pangea breaks up
200 mya- First Mammals appear
Precambrian
What are major geologic events
of the Mesozoic Era?
Answer Bank
•
•
•
•
200 mya- 1st Mammals
180 mya- Pangea breaks up
160 mya- 1st Birds
65 mya- Mass extinction 60% of all life
perishes including dinosaurs due to
large ______collision
Extinction
90%
Meteorites
Explosion
Fossil
Oxygen
Humans
Photosynthesis
Cenozoic Era
With Dinosaurs gone, Mammals would inherit
the earth and dominate the land
Large mammals thrive such as
Horses, Mammoths, and Primates
Mankind would evolve and inhabit
the earth expanding it’s population
Many Ice Ages came in went causing
the extinction of many large mammals
Precambrian
Major Geologic Events of the
Cenozoic Era
Precambrian
Major Geologic Events of the
Cenozoic Era
300,000 ya- Modern humans appear
7 mya- First Human Ancestors appear
45 mya- One of the largest Ice ages occur
Precambrian
What are major geologic
events of the Cenozoic Era?
• 45 mya- Major ice age event
• 7 mya- 1st Human ancestors
appear
• 300,000ya- 1st modern ____
• Present- your writing this down!!!!!
Answer Bank
Extinction
90%
Meteorites
Explosion
Fossil
Oxygen
Humans
Photosynthesis
Summarize:
List the events in order: Oldest to youngest
•
•
•
•
•
•
Mammals dominate the earth
Mass extinction 90% of all life wiped out
Reptiles dominate the earth
Explosion of life
Phytoplankton create oxygen rich atmosphere
Mass extinction 65% of all life wiped out including
dinosaurs