5.2.1 Principles of Relative Dating

Principles of Relative Dating

5.2.1

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Objectives

Learners can:

• describe the principles used to determine the relative ages of rocks and geologic events

• explain the significance of relative dating in understanding the sequence of geologic events and the history of the Earth

• fossil

• rock record

Prerequisite Vocab

• principles of relative dating

• relative dating

New Vocab

Vocabulary

​the principles used to determine the relative ages of rocks and geologic events

​​Principles of Relative Dating

the process of determining the relative ages of rocks and geologic events without using absolute dates

Relative Dating

Categorize

Options (4)

Drag to order the images beginning with the individual you think is the youngest to the individual you believe is the oldest.

Youngest

Younger

Old

Oldest

Open Ended

What clues did you use to sort the images?

Principles of Relative Dating

The principles of relative dating are used to determine the relative ages of rocks and geologic events.

Three principles used are:

• the law of superposition

• the law of cross-cutting relationships

• the law of inclusions

The law of superposition states that in an undisturbed sequence of sedimentary rocks, the oldest rocks are at the bottom, and the youngest rocks are at the top. This order happens because new layers of sediment cover up older layers as they are deposited.

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Law of Superposition

Labelling

According to the law of superposition, which layer of rock is the oldest and which is the youngest?

Drag labels to their correct position on the image

youngest

oldest

The law of cross-cutting relationships states that any geologic feature that cuts across another geologic feature is younger than the feature it cuts across. This is because the older feature must have already been there in order for the younger feature to cut across it.

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Law of Cross-Cutting Relationships

Fault lines run through the rock where the layers have shifted. The rock layers must have existed before the breaks happened for this to occur. Therefore, the fault lines are younger than the sedimentary layers.

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Fault Lines

Multiple Choice

TRUE OR FALSE: Any geologic feature that cuts across another geologic feature is younger than the feature it cuts across.

• true

• false

When making these cookies, the raisins are mixed into the batter before the cookies are baked. Once the cookies are solid through the baking process, the raisins are locked in. Nothing can be added to the cookies once they are baked.

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Cookies and the Add-ins

The law of inclusions states that any rock or mineral that is found within another rock or mineral is older than the rock or mineral that it is found in. This is because the rock or mineral located within must have formed before the rock or mineral that has since surrounded the original fragments.

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Law of Inclusions

Open Ended

Based on the Law of Inclusions, what conclusions can you make about the white quartz embedded into the dark grey rock in the picture?

Fill in the blank: Based on the Law of Inclusions, the quartz was formed ____________ (before/after) the grey rock.

Labelling

Label the rock layers based on when they were formed (1 = first, 5 = last)

Drag labels to their correct position on the image

5

4

3

2

1

​Relative Dating to Understand Earth

Relative dating is a method geologists use to determine the sequence of geological events that have occurred over time on Earth.

Geologists can examine the layers of rock and the fossils within them to determine the order in which the layers were deposited and the relative ages of fossils. With this information, they can create a geological timeline of Earth's history, highlighting major events that occurred over time.

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Sequence of Events

Geologists examine rock layers and their fossils to identify erosion or wearing away of rock, deposition or addition of new rock, and mountain building. For instance, if a layer of rock with marine fossils is found on top of a layer with terrestrial fossils, it suggests that the area was once underwater and later became a mountain range.

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Earth's Historical Processes

By studying the fossils in rock layers, geologists can identify the different species of plants and animals that have lived on Earth throughout its history. This information can be used to reconstruct the evolution of life on Earth and explore how different species have adapted and changed over time.

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History of Life