Law of Superposition

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Review:

In the study of Earth's history, scientists use two important methods to determine the age of geological specimens such as fossils. These two methods are the relative age and the absolute age.

• Relative age compares the age of different things without

giving a specific number.

• Absolute age tells the exact age of an object using

different techniques.

These two methods help scientists understand the timeline of events
on Earth and how things have changed over time.

Multiple Choice

Which statement MOST accurately describes the advantage of absolute dating methods?

• Absolute dating methods are simpler and less costly compared to relative dating

• Absolute dating relies solely on interpreting the local geological context

• Absolute dating provides a relative order of events without specific ages

• Techniques such as radiometric dating offer high accuracy in determining specific numerical ages

Multiple Choice

A geologist observes a fault that cuts across multiple layers of rock. Which principle is demonstrated?

• principle of superposition

• principle of cross-cutting relationships

• principle of original horizontality

• principle of lateral continuity

Multiple Choice

In which scenario would a geologist use relative dating methods?

• when dealing with a single geological layer

• when specific numerical ages are necessary

• when high accuracy is required

• when several horizontal layers of sedimentary rock are involved

Law of Superposition

Unit 3 Earth’s History

Lesson 3.7

Law of Superposition

Today we will

•explain the law of superposition and its role in relative dating

•identify the practical applications of the law of superposition

Vocabulary: archaeology

Prerequisite Vocabulary: geology, paleontology

Imagine a baker makes a
dozen fresh cookies every day
for a week and stores them in
a cookie jar.

Monday, the baker made chocolate chip
cookies.

Tuesday, they made sugar cookies

Wednesday, oatmeal raisins were made

Thursday, they made peanut butter

Friday, they wrapped up the week with an
everything monster-style cookie.

The bakery employees loved each type of
cookie but could not finish the whole batch
each day. So by the end of Friday, the jar
was full.

Applying this concept to
geology...

The age of the cookie depends on when
it was added to the cookie jar.

This age can be estimated based on the
different layers of each type of cookie,
and how close to the top of the jar they
are found.

Today we will learn more about how this
principle is applied to fields of science
such as geology and archaeology.

Notebook Pages 44-45

This layer of bedrock is considered the oldest in this
area. Due to the lack of fossils, it can be assumed that
this layer formed before life existed in this area.

This layer has fossils which are
considered the first examples
of life in this area.

The fossils found in this area
are considered the youngest
fossils and are relatively new
compared to the ones found
deeper in the ground.

Considering this layer
is the one that
supports present-day
life, it is the youngest
layer.

1

2

3

4

https://www.youtube.com/watch?v=V9orxSQa
dX4

Labelling

Label the order in which the layers were deposited in the image. Use number 1 to represent the oldest layer

Drag labels to their correct position on the image

1

2

4

3

Relative
Dating and
the Law of
Superposition

Remember, relative dating determines the
chronological order of events without
assigning specific numerical dates or ages.

Relative dating relies on principles such as
the law of superposition.

William Smith, an English geologist born in
1769, made groundbreaking contributions
to the field of geology, particularly in the
development of relative dating techniques.

William “Strata” Smith and

The map that changed the world

William “Strata” Smith’s
Map

https://viewer.gigamacro.com/view/y3kBXtiAXD6l5oWn?x1=1
4182.94&y1=-6788.74&res1=24.41&rot1=0.00

Multiple Choice

A scientist finds two similar fossils in rock layers a few miles apart from each other.

Which of the following methods would a scientist use to determine the relative age of the two fossils?

• analyze the chemical composition of the fossils

• conduct radiometric dating of the fossils

• apply the law of superposition to examine the rock layers

• compare the sizes of the fossils

Paleontology
and
Archaeology

Both paleontology and archaeology use evidence from the past to

learn more about what life was like and how societies

have developed over time.

Paleontology focuses on ancient life and examines fossils such as

bones and the remains of ancient plants to learn about life that

existed long ago.

Archaeology, on the other hand, focuses specifically on human history

by examining artifacts, structures, and remains left behind by

ancient civilizations.

As you watch the following video, think about how each of these fields

uses the law of superposition

https://www.youtube.com/watch?v=q6OjU8UvY
54

Categorize

Options (6)

fossilized bone

dinosaur tracks

imprint of an ancient leaf

arrowheads

pottery

preserved woven fabric

Categorize the following objects into the correct field of science that would study them.

paleontology

archaeology

Paleontology
and the Law
of
Superposition

Paleontology relies on the law of

superposition.

The next three slides screens will help us

learn how the law of superposition is
applied in paleontology with the help of:

• sequencing rock layers;

• analyzing connections between fossils; and

• understanding geological events.

Sequencing
Rock Layers

Paleontologists look at layers of
rock called strata and compare them to strata in many distant places.

The order of the rock layers provides
clues to help paleontologists figure out
the sequence of time.

- finding the same composition and
order of rock layers in different places
in the world suggests these layers were formed at the same time.

Analyzing Connections
Between Fossils

Paleontologists analyze the distribution of fossils in

sedimentary rocks to create a chronological

framework.

Look at the fossils of trilobite and starfish shown on

the right. Paleontologists examine and compare a

variety of fossil species to construct timelines of

evolution and extinction events within various

rock layers.

Understanding
Geological Events

The law of superposition helps paleontologists
understand the impact of geologic events
on ancient life.

For instance, if a rock layer contains fossils of
marine organisms far inland, it suggests that a sea
once covered the area.

Newer layers with different fossils, or the absence
of marine fossils, tell us the environment changed
over time due to geological events such as the
movement of Earth's crust or changes in sea level.

Multiple Choice

How do paleontologists rely on the law of superposition to estimate the age of fossils?

• by examining the vertical arrangement of matching rock layers in which fossils were found

• by analyzing the relative depths of fossils within each rock layer

• by studying the succession of fossils across various layers of sediment

Archaeology
and the Law
of
Superposition

Archaeologists use the law of superposition as a

guiding principle when exploring and excavating

archaeological sites. Let’s learn about three

notable archaeological excavations and how the

law of superposition was used in uncovering

human history:

• Pompeii: buried in ash;

• Troy: cities atop cities; and

• Teotihuacan: mysterious pyramids.

Pompeii: Buried in
Ash

• Pompeii, buried under volcanic ash after

a deadly eruption of Mount Vesuvius in
79 CE, is a remarkably preserved city that
provides insights into daily life during the
Roman Empire.

• Archaeologists have developed a timeline

of events leading up to the eruption by
analyzing the different layers and
artifacts. The archaeologists also used
the law of superposition to determine the
timeline of the city's occupation, its
buildings, and the activities of its
inhabitants.

Troy: Cities Atop Cities

The site of Troy, made famous by Homer's epic poem
The Iliad, is situated over layers of ancient cities that
provide archaeological evidence of a long history of
human occupation.

The archaeologists who excavated Troy relied on the
law of superposition to study the numerous
settlements built on top of each other.

Using the law of superposition helped the
archaeologists identify different periods of occupation,
confirming the existence of multiple cities at the site
over time.

Teotihuacan:
Mysterious Pyramids

The ancient Mesoamerican city boasts an impressive
historic collection of pyramids, including the Pyramid of
the Sun and the Pyramid of the Moon.

These pyramids offer insights into the Mesoamerican
civilization that inhabited this region. The law of
superposition helped archaeologists understand the
sequence of development and construction of the
pyramids and structures at Teotihuacan.

By examining the layers of construction and occupation,
researchers have pieced together the timeline of the city's
growth and expansion from around 200 BCE to 750 CE.

Labelling

Fill in the blanks

Drag labels to their correct position on the image

paleontology

strata

oldest

human

archaeology

youngest

Environmental
Science and
the Law of
Superposition

Environmental scientists apply the law
of superposition in various ways to
understand the history of change in
landscapes through sediment
deposition and ecological patterns.

Multiple Choice

How does environmental science rely on the law of superposition to learn about change over time in landscapes and ecosystems?

• by studying the order of fossils in ancient human settlements

• by analyzing the layers of sediment in archaeological sites

• by studying the sequence of rock layers in volcanoes

• by examining the layers of soil and sediment to reconstruct past environmental conditions

Multiple Choice

What does the law of superposition state about the arrangement of rock layers?

• The oldest rocks are at the top

• The oldest rocks are in the middle.

• The youngest rocks are at the bottom.

• The youngest rocks are at the surface.

Multiple Choice

Which branch of science relies on the law of superposition to determine the relative age of objects made by humans, the relative age of soils, and the order of ecological changes that have affected humans?

• biogeography

• environmental science

• archaeology

• paleontology

Summary

In today's lesson, you learned about:

• the law of superposition and its role in

relative dating;

• how it allows geologists to determine the

relative ages of sedimentary rock layers
and the fossils within them; and

• the practical applications of the law of

superposition in fields such as
paleontology, archaeology, and
environmental science.

In an upcoming lesson, you will learn about
radioactive dating and half-life.

Completed Notes 44-45