RELATIVE AND ABSOLUTE DATING OF ROCKS / EARTH AND LIFE SCIENCE / SCIENCE 11 - MELC 12 & 13

Summary

This 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

• 📚 The video introduces two primary methods for determining the age of rocks: relative dating and absolute dating, crucial for understanding geological time subdivisions.
• 🔍 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.
• 📈 Absolute dating uses radioactive decay to provide a numerical age for rocks and fossils, offering a precise measurement of time past.
• 🏞️ 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.
• ✂️ 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.
• 🔨 The law of inclusion suggests that fragments or inclusions within a rock layer are older than the layer itself, another aspect of relative dating.
• 🌿 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.
• 🌊 The law of original horizontality posits that sedimentary layers are originally deposited horizontally, and deviations indicate geological disturbances.
• ⚛️ Radiometric dating, a type of absolute dating, uses the known decay rates of radioactive isotopes to calculate the age of rocks and fossils.
• 📉 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.
• 🌐 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

00:00

📚 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.

05:00

🔍 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.

10:02

🗓️ 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.

Keywords

💡Relative Dating

Relative dating is a method used by geologists to determine the sequence of geological events without necessarily knowing their absolute age. It involves identifying the order in which layers of rock were deposited. In the video, relative dating is exemplified by the law of superposition, where the youngest rock layer is on top and the oldest at the bottom, as seen in the Grand Canyon example.

💡Absolute Dating

Absolute dating is a technique that provides a numerical age or range in years for the age of a rock, fossil, or archaeological artifact. It is often done using radiometric dating, which measures the decay of radioisotopes. The video explains that absolute dating gives a specific age, like stating a trilobite fossil is 489 million years old, as opposed to relative dating which would only tell us it is older than a dinosaur tooth fossil.

💡Law of Superposition

The law of superposition is a fundamental principle in geology stating that in any undisturbed sequence of rocks, the oldest layer is at the bottom and the layers get progressively younger as you move upward. The video script uses the Grand Canyon as an example to illustrate this principle, showing how geologists can determine the relative ages of rock layers.

💡Radioactive Decay

Radioactive decay is a process in which an unstable atomic nucleus loses energy by emitting radiation. In the context of the video, it is the basis for radiometric dating, where the decay of radioactive isotopes like uranium-238 and potassium-40 is used to determine the absolute age of rocks. The half-life of these isotopes is known, and by measuring the ratio of parent to daughter isotopes, geologists can calculate the rock's age.

💡Half-life

Half-life is the time required for half of a given amount of a radioactive substance to decay. It is a key concept in radiometric dating, as it allows geologists to calculate the age of rocks and fossils. The video mentions the half-life of uranium-238 as 4.5 billion years and uses it to explain how geologists can determine the age of Earth's oldest rocks.

💡Stratified Rocks

Stratified rocks are layers of sedimentary rock that have been deposited over time. The video script discusses how the study of these rocks through relative and absolute dating methods helps geologists understand the sequence of geological events and the age of the Earth. The Grand Canyon is given as an example of stratified rocks following the law of superposition.

💡Fossils

Fossils are the preserved remains or traces of animals, plants, and other organisms from the past. In the video, fossils are used as a basis for relative dating, where the type of fossils found in rock layers can indicate the age of those layers. The script also mentions how the presence of different types of fossils in different rock layers contributes to the creation of the geologic time scale.

💡Geologic Time

Geologic time refers to the concept of time that spans the 4.6 billion-year history of Earth. The video script explains how geologists use relative and absolute dating methods to determine subdivisions of geologic time, such as the Jurassic period, which helps in understanding the sequence of life and events on Earth.

💡Radiometric Dating

Radiometric dating is a technique used to date materials such as rocks, usually based on a comparison between the amount of parent isotopes and daughter isotopes in the material. The video script describes how carbon-14 dating is used for younger fossils, while uranium-238 and potassium-40 are used for older rocks, providing a way to determine the numerical age of geological specimens.

💡Luminescence Dating

Luminescence dating is a method used to determine the age of sediments by measuring the amount of light emitted from the sediment when it is heated. The video script mentions this process as a way to date rocks and provides insights into the energy stored in rocks, which can be used to understand past environmental conditions.

💡Geologic Time Scale

The geologic time scale is a system of chronological measurement used by geologists, archaeologists, and other Earth scientists to describe the timing and relationships of events that have occurred during Earth's history. The video script explains how the scale is created by ordering rock layers from oldest to youngest and how it helps in understanding the changes in life and environments over time.

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

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you