4B3 Evidence for the History of the Earth

Question 1

What is the purpose of relative dating?

Answer 1

To determine the relative order of events in Earth’s history.

Relative dating places geological events in the correct sequence without providing exact dates.

Question 2

What type of rocks are typically studied using relative dating?

Answer 2

Sedimentary rocks

Sedimentary rocks form in layers, making it easier to establish the relative age of each layer.

Question 3

What does the principle of superposition help establish?

Answer 3

The relative age of rock layers.

The oldest layers are typically found at the bottom, with progressively younger layers above them.

Question 4

What does the principle of original horizontality state?

Answer 4

Sediments are initially deposited in flat layers.

This principle states that sediments are deposited horizontally, and any tilting or folding indicates post-depositional geological processes.

Question 5

True or False:

Superposition applies to all sedimentary and igneous rocks.

Answer 5

False

The principle of superposition applies mainly to sedimentary rocks and surface-deposited igneous rocks like lava flows. It doesn’t apply to intrusive igneous rocks (e.g., dikes or sills) or highly deformed rock sequences.

Question 6

What principle states that sedimentary layers extend horizontally until they thin out?

Answer 6

Lateral continuity

This principle allows for the correlation of rock layers across large areas.

Question 7

Fill in the blank:

Fossils are most commonly found in ________ rocks.

Answer 7

sedimentary

Sedimentary rocks preserve fossils due to their formation process.

Question 8

What is the principle of fossil succession?

Answer 8

Fossils appear in a specific order within the rock record.

This principle allows geologists to identify and correlate rock layers using fossils.

Question 9

What is an unconformity?

Answer 9

A gap in the rock record.

Unconformities occur due to erosion or a lack of deposition over time. There are many different kind of uncomformities, including discomforities or nonconformities.

Question 10

Fill in the blank:

A/an _________ occurs between two layers of sedimentary rock with a gap in deposition.

Answer 10

disconformity

Disconformities are uncomforities that represent periods of erosion or non-deposition between parallel sedimentary layers.

Question 11

What is a nonconformity?

Answer 11

It occurs where sedimentary rocks cover eroded igneous or metamorphic rocks.

Nonconformities are a kind of uncomfomity that signify significant geologic time gaps.

Question 12

What is correlation in geology?

Answer 12

Matching rock layers across different areas.

Geologists use fossils and rock characteristics to establish connections.

Question 13

True or False:

Index fossils are key for identifying and correlating rock layers.

Answer 13

True

Index fossils are widespread, short-lived, and unique to specific time periods.

Question 14

Which principle shows faults are younger than the layers they cut?

Answer 14

Cross-cutting relationships

This principle states that a fault or intrusion is younger than the layers it cuts through.

Question 15

Fill in the blank:

______ fossils are critical for correlating distant rock layers.

Answer 15

Index

These fossils, like trilobites and ammonites, help identify and match rock layers across regions.

Question 16

What is the principle of inclusions?

Answer 16

Fragments within a rock are older than the rock itself.

Inclusions form when pieces of older rock become embedded in newer rock.

Question 17

True or False:

Intrusions are always older than the surrounding rock layers.

Answer 17

False

Intrusions are younger as they cut through pre-existing layers.

Question 18

What principle explains the sequence in folded layers?

Answer 18

Original horizontality

Layers are initially deposited flat, and folding happens later.

Question 19

What is the significance of a stratigraphic column?

Answer 19

It shows the sequence and relative ages of rock layers in an area.

A stratigraphic column is a visual representation that helps geologists analyze and compare the relative ages of different layers of rock.

Question 20

Fill in the blank:

The _____ of a rock layer is determined by its position relative to other layers.

Answer 20

age

Determining the relative age of rocks relies on principles like superposition and cross-cutting.

Question 21

True or False:

Relative dating provides specific numerical ages for rock layers.

Answer 21

False

Relative dating only establishes the sequence of events, not their exact age.

Question 22

True or False:

Fossils can be used to directly measure the age of rock layers.

Answer 22

False

Fossils help establish the relative age of rock layers, but not the exact age. Radiometric dating is used for that purpose.

Question 23

What does absolute dating determine?

Answer 23

The actual age of a rock or fossil.

Absolute dating provides a precise age using methods like radiometric dating.

Question 24

What is radiometric dating?

Answer 24

A method of dating based on radioactive isotope decay.

Radiometric dating relies on the predictable rate of decay of radioactive isotopes in minerals.

Question 25

# Fill in the blank: Radiometric dating **uses** \_\_\_\_\_\_\_ to measure isotope decay rates.

Answer 25

half-life ## Footnote **Half-life** is the time required for half of a radioactive isotope to decay, a key concept in radiometric dating.

Question 26

# True or False: An isotope's half-life **changes** with temperature or pressure.

Answer 26

False ## Footnote The half-life of an isotope is **constant** and is unaffected by environmental conditions like temperature or pressure.

Question 27

Which **isotope** is commonly used to date rocks older than 100,000 years?

Answer 27

Uranium-238 ## Footnote **Uranium-238** decays to lead-206 and is commonly used for dating rocks millions to billions of years old.

Question 28

What is the **parent isotope** in radiometric dating?

Answer 28

The radioactive isotope that **decays** into a stable daughter isotope. ## Footnote The parent isotope undergoes *radioactive decay* to form a stable daughter isotope, which helps determine the age of a sample.

Question 29

# Fill in the blank: Carbon-14 dating is primarily **used** for dating \_\_\_\_\_\_\_ materials.

Answer 29

organic ## Footnote Carbon-14 dating is effective for dating **organic** materials like wood, bone, and cloth, typically up to 50,000 years old.

Question 30

# True or False: Carbon-14 can be **used** to date rocks older than 100,000 years.

Answer 30

False ## Footnote Carbon-14 dating is only effective for relatively **recent** fossils or materials (up to about 50,000 years).

Question 31

Which **rock** type is most commonly used for radiometric dating?

Answer 31

Igneous rocks ## Footnote *Igneous rocks* are formed from the cooling of molten magma, trapping radioactive isotopes in minerals.

Question 32

What is the **age** of the Earth according to radiometric dating?

Answer 32

Approximately 4.54 billion years. ## Footnote Radiometric dating of the oldest rocks and meteorites has provided a consistent age for the Earth of about 4.54 billion years.

Question 33

What is an **example** of an isotope used for dating very old rocks?

Answer 33

Potassium-40 ## Footnote **Potassium-40** decays to Argon-40 and is used to date rocks older than 100,000 years, especially volcanic rocks.

Question 34

# True or False: Radiometric dating is the **only** method used to determine the age of rocks.

Answer 34

False ## Footnote While radiometric dating is a widely used and accurate method, other methods like **stratigraphy** are also used in conjunction.

Question 35

# Fill in the blank: The parent-to-daughter isotope ratio helps **determine** the \_\_\_\_\_ of a sample.

Answer 35

age ## Footnote By measuring the ratio of parent to daughter isotopes, scientists can *calculate* the age of the sample with high precision.

Question 36

Which element's **isotopes** are used for dating very old meteorites?

Answer 36

Uranium ## Footnote Uranium isotopes, such as Uranium-238, are used for dating meteorites and rocks as old as the solar system.

Question 37

What does radiometric dating **rely** on for accurate results?

Answer 37

The **constant** rate of decay of isotopes. ## Footnote The rate at which isotopes decay (half-life) remains constant, providing a *reliable* means to measure age.

Question 38

How is the age of the sample **calculated** in radiometric dating?

Answer 38

By **measuring the ratio** of parent to daughter isotopes. ## Footnote The ratio provides the time elapsed since the rock or mineral *crystallized*, allowing the age to be calculated.

Question 39

# Fill in the blank: \_\_\_\_\_\_\_\_ \_\_\_\_\_\_ is an important **method** for dating ancient igneous rocks.

Answer 39

Potassium-argon dating ## Footnote *Potassium-argon dating* is effective for dating ancient igneous rocks, as potassium-40 decays into argon-40 over time.

Question 40

# True or False: Radiometric dating can **only** be used on rocks and not fossils.

Answer 40

False ## Footnote Radiometric dating cannot **directly date** fossils because they lack radioactive isotopes. However, it can determine a fossil’s age indirectly by dating minerals in surrounding rocks or volcanic ash layers.

Question 41

What is the main **advantage** of radiometric dating?

Answer 41

It provides **precise and accurate** numerical ages. ## Footnote Radiometric dating offers a reliable, exact age, unlike relative dating, which only determines the sequence of events.

Question 42

What is an example of a **radioactive isotope with a short half-life**?

Answer 42

Carbon-14 ## Footnote **Carbon-14** has a short half-life of about 5,730 years, making it suitable for dating relatively recent organic material.

Question 43

# True or False: Radiometric dating can **only** be performed on rock samples that have not undergone metamorphism.

Answer 43

True ## Footnote Metamorphism can reset the radioactive clock, making it *challenging* to date metamorphosed rocks. However, certain isotopic systems, like uranium-lead in zircon, can remain unaffected and provide accurate dates in some cases.

Question 44

What does the **presence of daughter isotopes** in a sample indicate?

Answer 44

That some **time has passed** since the rock or mineral crystallized. ## Footnote The daughter isotopes accumulate over time, and their presence allows scientists to calculate the age of the sample.

Question 45

What types of radiation can be **emitted** during isotope decay?

Answer 45

1. Alpha radiation 2. Beta radiation 3. Gamma radiation ## Footnote These types of radiation are emitted as the parent isotopes *decay* to form stable daughter isotopes.

Question 46

# True or False: Radiometric dating can be used to directly date **sedimentary** rocks.

Answer 46

False ## Footnote Radiometric dating is typically used on igneous and metamorphic rocks. Sedimentary rocks are dated *indirectly* using the ages of the layers around them.

Question 47

What does a **stable isotope state** mean in radiometric dating?

Answer 47

The isotope has fully **decayed** into a non-radioactive element. ## Footnote Once an isotope decays into a stable daughter isotope, the radioactive decay process is *complete*, allowing scientists to calculate the age of the material.

Question 48

What is a **closed system**?

Answer 48

A system where **no isotopes are added or lost** over time. ## Footnote For radiometric dating to be accurate, the sample must be a closed system, meaning that no parent or daughter isotopes have been *exchanged* with the environment.