RELATIVE AND ABSOLUTE DATING OF ROCKS / EARTH AND LIFE SCIENCE / SCIENCE 11 - MELC 12 & 13
Summary
TLDRThis educational video introduces two primary methods geologists use to determine the age of rocks: relative dating and absolute dating. Relative dating establishes the sequence of geological events, while absolute dating provides numerical ages using radioactive decay. The script explains principles like the law of superposition and the use of fossils to create a geologic time scale. It also highlights how radiometric dating with isotopes like uranium-238 and carbon-14 helps in accurately determining the age of rocks and fossils, contributing to our understanding of Earth's history.
Takeaways
- π The video introduces two primary methods for determining the age of rocks: relative dating and absolute dating, crucial for understanding geological time subdivisions.
- π Relative dating is based on the sequence of geological events and the order of rock layers, helping to determine which event or fossil is older without a numerical age.
- π Absolute dating uses radioactive decay to provide a numerical age for rocks and fossils, offering a precise measurement of time past.
- ποΈ The law of superposition is a fundamental principle of relative dating, stating that in a sequence of undisturbed sedimentary layers, the oldest is at the bottom and the youngest at the top.
- βοΈ The law of cross-cutting relationships indicates that an igneous intrusion is younger than the rock it cuts through, helping in establishing the relative ages of rock formations.
- π¨ The law of inclusion suggests that fragments or inclusions within a rock layer are older than the layer itself, another aspect of relative dating.
- πΏ The law of faunal succession is used in relative dating, where the appearance of different fossil groups in rock layers helps to determine their relative ages.
- π The law of original horizontality posits that sedimentary layers are originally deposited horizontally, and deviations indicate geological disturbances.
- βοΈ Radiometric dating, a type of absolute dating, uses the known decay rates of radioactive isotopes to calculate the age of rocks and fossils.
- π Half-life, the time required for half of a radioactive isotope to decay, is a key concept in understanding how radiometric dating provides numerical age estimates.
- π The combination of relative and absolute dating methods allows geologists to create a more accurate and comprehensive geologic time scale, reflecting the history of life and changes on Earth.
Q & A
What are the two primary methods used by geologists to determine the age of rocks?
-The two primary methods used by geologists to determine the age of rocks are relative dating and absolute dating.
How does relative dating differ from absolute dating?
-Relative dating determines the sequence of age in geologic time by identifying the relative order of events, while absolute dating determines the numerical age of rocks using radioactive decay.
What is the Law of Superposition and how does it apply to relative dating?
-The Law of Superposition states that each layer of sediments is deposited on top of another, making the top layer the youngest and the bottom layer the oldest. This principle is fundamental to relative dating as it helps establish the sequence of geological events.
Can you explain the Law of Cross-cutting relationships in the context of relative dating?
-The Law of Cross-cutting relationships states that an igneous intrusion is always younger than the rock it cuts across. This principle helps in determining the relative ages of rock formations and intrusions.
What does the Law of Inclusion tell us about the relative ages of rocks?
-The Law of Inclusion states that rocks or materials that are incorporated into the formation of sediments, known as inclusions, are always older than the layer of sediments in which they are embedded.
How does the principle of faunal succession contribute to the understanding of geologic time?
-Faunal succession is the principle that fossils of plants and animals are grouped according to the period of geologic time they appeared. Strata containing these groups of fossils are formed during that particular time, aiding geologists in creating the geologic time scale.
What is the Law of Original Horizontality and its relevance to the study of rock layers?
-The Law of Original Horizontality states that layers of sediments are originally deposited horizontally. Any deviation from this indicates that the strata may have been deformed by the movement of the Earth's crust.
How does radiometric dating contribute to absolute dating?
-Radiometric dating is a technique used in absolute dating that measures the proportion of parent and daughter isotopes present in a rock to determine its age based on the known decay rates of radioactive isotopes.
What is the significance of the half-life of a radioactive isotope in dating rocks?
-The half-life of a radioactive isotope is the time it takes for half of the original isotope to decay into a more stable daughter isotope. This fixed rate of decay is crucial for calculating the age of rocks in absolute dating.
Why is carbon-14 used in dating fossils, and what is its half-life?
-Carbon-14 is used in dating fossils because it is a radioactive isotope that was part of the living organism's carbon cycle. It has a half-life of 5730 years, making it suitable for dating relatively recent organic remains.
How do geologists use both relative and absolute dating to create a more accurate geologic time scale?
-Geologists use relative dating to establish the order of geological events and absolute dating to determine the exact age of rocks. By combining these methods, they can create a more accurate and comprehensive geologic time scale that reflects both the sequence and timing of Earth's history.
Outlines
π Introduction to Rock Dating Methods
This paragraph introduces the topic of the video, which is about the methods used to determine the age of rocks: relative dating and absolute dating. It explains that these methods help geologists understand the subdivisions of geologic time. The paragraph also poses a question about how geologists can determine events from the distant past when modern technology was not available. It highlights the importance of understanding the sequence of geological events and the difference between relative and absolute dating methods, with relative dating focusing on the order of events and absolute dating providing numerical ages through radioactive decay.
π Principles of Relative and Absolute Dating
This paragraph delves into the principles behind relative dating, such as the law of superposition, cross-cutting relationships, the law of inclusions, and fossil succession. It explains how these laws help determine the sequence of geological events. The paragraph also discusses absolute dating, specifically radiometric dating, which uses radioactive isotopes to determine the numerical age of rocks and fossils. It provides examples of different isotopes used, such as carbon-14 for dating fossils and uranium-238 for dating rocks, and explains the concept of half-life in the context of radioactive decay.
ποΈ Geologic Time Scale and the Role of Dating Methods
The final paragraph discusses how the understanding of relative and absolute dating methods contributes to the creation of the geologic time scale. It explains that by observing the order of fossils in rock layers, scientists were able to establish the sequence of life on Earth. The paragraph also touches on how the discovery of radioactivity allowed scientists to measure the exact age of rocks, providing a more precise timeline for Earth's history. It concludes by emphasizing the importance of these dating methods in understanding the changes in Earth's climate and environment over time.
Mindmap
Keywords
π‘Relative Dating
π‘Absolute Dating
π‘Law of Superposition
π‘Radioactive Decay
π‘Half-life
π‘Stratified Rocks
π‘Fossils
π‘Geologic Time
π‘Radiometric Dating
π‘Luminescence Dating
π‘Geologic Time Scale
Highlights
Introduction to methods used to determine the age of rocks: relative and absolute dating methods.
Relative dating determines the sequence of geological events without numerical ages.
Absolute dating provides a numerical age for rocks using radioactive decay.
The difference between relative and absolute dating illustrated with the red and grey car analogy.
Principles of relative dating include the law of superposition, cross-cutting relationships, and the law of inclusion.
Law of superposition states that in a sequence of undisturbed sedimentary layers, the oldest is at the bottom.
Cross-cutting relationships indicate that an intrusion is younger than the rock it cuts through.
Law of inclusion suggests that fragments in sedimentary rocks are older than the rock itself.
Fossil succession is used to correlate rock layers based on the age of fossils found within them.
Law of original horizontality states that sedimentary layers are originally deposited horizontally.
Radiometric dating is the primary method of absolute dating, using isotopes for age determination.
Carbon-14 dating is used for determining the age of fossils, with a half-life of 5730 years.
Uranium-238 and potassium-40 are used for dating older rocks, with half-lives of 4.5 billion and 1.251 billion years respectively.
Half-life is the time required for half of a radioactive substance to decay.
Geologists use both relative and absolute dating for comparison and verification to determine accurate rock ages.
Luminescence dating measures the light emitted from energy stored in rocks, providing additional dating methods.
Similarities in fossils found in different rock layers worldwide led to the creation of the geologic time scale.
The Jurassic period is identified as a time of abundant dinosaur life, dated between 205 and 142 million years ago.
Relative time refers to the physical subdivisions of rocks and the order of geological events.
Transcripts
hello grade 11
welcome in this video you will learn
about the methods
used to determine the age of rocks the
relative method
and the absolute dating method and you
will also learn
how these methods help geologists in
determining the subdivisions of the
geologic time
[Music]
our discussion will focus on the
following learning competencies
one describe the different methods used
to determine the age of stratified rocks
and two explain how relative and
absolute dating were used to determine
the subdivision of geologic time
have you ever wondered how we were able
to know what happened thousands or
millions
or even billions of years ago
that was the time when technologies we
have today are not yet
available and even humans do not exist
yet
but how did geologists come up with the
records of the past events
determining the age of stratified drops
using two methods the relative dating
and the absolute painting
help geologists know the sequence of age
in geologic time
now what is the difference between these
two methods
relative dating is a method of
determining the age of rocks in each
layer by identifying the relative order
of previous
events
absolute dating however is a method of
determining the numerical age of rocks
using radioactive decay now let's
discuss
further how these two differ relative
dating is determining which
fossil or event came first second third
etc
while absolute dating is determining the
actual age of rock
using radioactive decay when we say the
trilobite fossil is older than the
dinosaur tooth
fossil this is relative but when we say
the trilobite fossil is 489 million
years
old that's absolute let's take a look at
these two cars
the red car and the grey car when we say
the red car costs
ninety thousand dollars and the silver
car costs fifteen dollars
this is what method yes
absolute but when we say
the red car is more expensive than the
silver car
this one is
yes relative in determining the age of
rocks these two methods are also used
when the geologists say that this layer
is 225 million years old
this one is an absolute dating
but when the geologists say this layer
is older
than this layer this one is relatively
dating
now you see the difference between the
two absolute dating is
determined through radioactive detail
while relative dating is
through geologic sequencing the
determination of relative edges of rocks
are based on the following
principles now we have the law of
superposition
it states that each layer of sediments
is piled on top of another
layer making the one on top of the
strata the youngest one
while the layer at the bottom of the
strata as the oldest
as you can see in the illustration an
example of stratified rocks following
the law of superposition is found in the
grand canyon
[Music]
next is the law of cross-cutting
relationship which
states that an igneous intrusion is
always younger than the rock it cuts
across
a lava that cooled and hardened on its
surface
is called an extrusion the strata
beneath the extrusion are always
older while a magma that cooled and
hardened beneath the surface
is called an intrusion an igneous
intrusion is always
younger than the rock it has intruded
this is also true to faults a fault a
break on the earth's crust
is always younger than the stratified
rock that it comes
next is the law of inclusion the rocks
that mixed up in the formation of
sediments are called
inclusions these rocks are always older
than the layer of sediments
it is embedded the pebbles in this
conglomerate are older than the
conglomerate itself
next we have the final succession
fossils of plants and animals are
grouped according to the period of
geologic time they appeared
strata containing those group of fossils
are also formed on that particular
period of time
this becomes the basis of geologists in
creating the geologic time scheme
we also have the law of original
horizontality
according to this layers of sediments
are originally deposited horizontally
those strata that are found not in
horizontal order
may have been deformed by the movement
of the earth's crust
in absolute dating the most common way
of determining the absolute age of
rock is through radiometric dating where
radioactive isotopes
found in fossils or rocks are used
carbon 14
is used to determine the age of fossils
while uranium-238
for rocks for example uranium-238 will
take 4.5 billion years
for half the amount of it to decay into
a daughter isotope led 206
[Music]
radioactive decay refers to the process
by which an atomic nucleus of an
unstable atom loses energy
half-life refers to the period of time
it takes for a substance undergoing
decay to decrease
by half radioactive isotopes
called parent isotope are unstable and
gradually decays
in a fixed rate into a daughter isotope
which is more
stable in the illustration is
another isotope of uranium the
uranium-235 which has a half-life of 700
million years
and decays into a stable isotope
lead to oa since the rates of decay of
radioactive isotopes are known
it can be used to determine the age of
rocks by measuring the proportion of
parent and daughter isotopes present
in rocks
for example if iraq is found to contain
the same proportion of uranium-238
and lead 206 geologists can
tell the age of rock is about 4.5
billion years old
since some rocks on earth's surface were
found in different timelines
other isotopes with a different rate of
decay are used like potassium 40 with a
half-life of 1.251 billion years
and uranium-235 mentioned earlier
with a half-life of 700 million years
carbon 14 with a half-life of 5730 years
is also used in dating remains of plants
and animals
this is called carbon dating
determining the subdivision of geologic
time using relative
and absolute dating to get more accurate
age of rocks geologists both
use the relative and absolute dating for
comparison and verification
determining the age of sedimentary rocks
using uranium-238 and potassium-40
sometimes leads to the age of its
component rocks
the metamorphic and igneous rocks not
the age of sediment accumulation
that is why geologists use as other
radioactive isotopes like carbon 14
to date the age of the fossils in the
sediments
and through the process called
luminescence dating
a process that measures the quantity of
emitted light from energy stored
in a rock the clues in rocks help
scientists put together a picture of how
places on earth have
changed scientists noticed in the 1700s
and 1800s that similar
layers of sedimentary rocks all over the
world contain
similar fossils they used relative
dating to order the rock players from
oldest to youngest
and they saw that the fossils in older
rocks
are different from the fossils in
younger rocks
for example older rock layers contain
only reptile fossils but
younger rock layers may also contain
mammal fossils
scientists divided earth's history into
several chunks of time when the fossils
showed similar things
living on the earth they gave each chunk
of time a name to help them
keep track of how earth has changed
for example one chunk of time when many
dinosaurs lived is called the jurassic
we find fossils of earth's first green
plants from the chunk of time name or
division
ordering the rock players from oldest to
youngest was a
first step in creating the geologic time
scale
it showed the order in which life on
earth
changed it also showed us on how certain
areas changed over time
in regard to climate or type of
environment
however the early geologic time scale
only showed the order of events
it did not show the actual years that
events
happened with the discovery of
radioactivity in the late 1800s
scientists were able to measure the
exact age
in years of different rocks
the jurassic period occurs after
triassic period
and before the cretaceous period and
spans the time from about 205 million
years ago
to about 142 million years ago
relative time is the physical
subdivisions of the rocks
found in the earth's geology and the
time and order of
events they represent
and that ends our lesson congratulations
i hope you learned something today
thank you for watching
[Music]
you
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