4A3 The History of Planet Earth

Question 1

Define:

stratigraphy

Answer 1

The study of rock layers and their sequence.

Stratigraphy helps determine the relative ages of geological formations and understand Earth’s history by interpreting the sequence of geological events and the formation of different layers.

Question 2

What does the principle of superposition help establish?

Answer 2

The relative age of rock layers.

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

Question 3

What does the principle of original horizontality state?

Answer 3

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 4

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

Answer 4

Lateral continuity

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

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

Fill in the blank:

Fossils are most commonly found in ________ rocks.

Answer 6

sedimentary

Sedimentary rocks preserve fossils due to their formation process.

Question 7

What is the principle of fossil succession?

Answer 7

Fossils appear in a specific order within the rock record.

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

Question 8

What is an unconformity?

Answer 8

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 9

Fill in the blank:

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

Answer 9

disconformity

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

Question 10

What is a nonconformity?

Answer 10

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

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

Question 11

What is correlation in geology?

Answer 11

Matching rock layers across different areas.

Geologists use fossils and rock characteristics to establish connections.

Question 12

True or False:

Index fossils are key for identifying and correlating rock layers.

Answer 12

True

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

Question 13

Fill in the blank:

______ fossils are critical for correlating distant rock layers.

Answer 13

Index

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

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

What is the principle of inclusions?

Answer 15

Fragments within a rock are older than the rock itself.

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

Question 16

True or False:

Intrusions are always older than the surrounding rock layers.

Answer 16

False

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

Question 17

What principle explains the sequence in folded layers?

Answer 17

Original horizontality

Layers are initially deposited flat, and folding happens later.

Question 18

What is the significance of a stratigraphic column?

Answer 18

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 19

When did Earth’s earliest eon occur?

Answer 19

About 4.6 billion years ago.

Known as the Hadean Eon, this period was marked by intense heat, volcanic activity, and asteroid bombardment before the first stable crust formed.

Question 20

What happens during a glaciation period?

Answer 20

Ice sheets expand, sea levels drop, and global temperatures decrease.

Glaciation can last for thousands to millions of years, shaping landscapes through erosion and deposition.

Question 21

True or False:

The Ice Age refers to a single glaciation event in Earth’s history.

Answer 21

False

Earth has experienced multiple Ice Ages, with cycles of glacial and interglacial periods over millions of years.

Question 22

Define:

mass extinction

Answer 22

A widespread and rapid decrease in biodiversity on Earth.

Mass extinctions occur when a large percentage of species disappear in a short geological period, often due to catastrophic events like asteroid impacts or climate changes.

Question 23

Why was the Permian-Triassic extinction significant?

Answer 23

The most severe extinction, wiping out most species.

Also called The Great Dying, it occurred ~252 million years ago, wiping out ~90% of marine and ~70% of land species, likely due to massive Siberian volcanic eruptions causing climate disruptions.

Question 24

List the five major mass extinction events in Earth’s history.

Answer 24

1. Ordovician-Silurian (443 Mya)
2. Devonian (375 Mya)
3. Permian-Triassic (252 Mya)
4. Triassic-Jurassic (201 Mya)
5. Cretaceous-Paleogene (66 Mya)

Mya=Million years ago

Ordovician-Silurian (443 Mya) – The extinction that wiped out many ocean species.

Devonian (375 Mya) – The event that severely affected marine ecosystems.

Permian-Triassic (252 Mya) – The largest extinction, eliminating most life on Earth.

Triassic-Jurassic (201 Mya) – The transition that allowed dinosaurs to thrive.

Cretaceous-Paleogene (66 Mya) – The impact that led to the non-avian dinosaurs’ extinction.

Question 25

What is the **Chicxulub impact**?

Answer 25

An **asteroid impact** linked to dinosaur extinction. ## Footnote Occurred 66 million years ago when a 10 km-wide asteroid hit the Yucatán Peninsula, triggering fires, tsunamis, and a global climate shift.

Question 26

Why do asteroid impacts **cause** global climate disruptions?

Answer 26

They **block sunlight** with dust and debris. ## Footnote This alters climate patterns, as seen in the Chicxulub impact, which likely caused a *nuclear winter* and food chain collapse.

Question 27

# True or False: The dinosaurs became **extinct** solely due to an asteroid impact.

Answer 27

False ## Footnote While the asteroid impact was a major factor, *volcanic activity* (Deccan Traps), *climate change* and *ocean acidification* also played crucial roles in their extinction.

Question 28

What is the **Deccan Traps**?

Answer 28

A massive **volcanic region** in India. ## Footnote Erupted around the time of the Chicxulub impact, releasing greenhouse gases that may have *contributed* to dinosaur extinction.

Question 29

What is the purpose of **relative dating**?

Answer 29

To determine the relative **order of events in Earth's history**. ## Footnote *Relative dating* places geological events in the correct sequence without providing exact dates.

Question 30

# Fill in the blank: The \_\_\_\_\_ of a rock layer is **determined** by its position relative to other layers.

Answer 30

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

Question 31

# True or False: Relative dating provides **specific numerical ages** for rock layers.

Answer 31

False ## Footnote Relative dating only establishes the **sequence** of events, not their exact age.

Question 32

# True or False: Fossils can be used to **directly** measure the age of rock layers.

Answer 32

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

Question 33

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

Answer 33

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

Question 34

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

Answer 34

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

Question 35

What **type of rocks** are typically studied using relative dating?

Answer 35

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

Question 36

What does **absolute dating** determine?

Answer 36

The **actual age** of a rock or fossil. ## Footnote Absolute dating provides a *precise* age using methods like radiometric dating.

Question 37

What is **radiometric dating**?

Answer 37

A method of dating based on **radioactive isotope decay**. ## Footnote Radiometric dating relies on the predictable *rate of decay* of radioactive isotopes in minerals.

Question 38

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

Answer 38

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

Question 39

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

Answer 39

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

Question 40

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

Answer 40

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

Question 41

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

Answer 41

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 42

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

Answer 42

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

Question 43

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

Answer 43

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 44

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

Answer 44

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

Question 45

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

Answer 45

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

Question 46

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

Answer 46

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 47

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

Answer 47

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

Question 48

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

Answer 48

False ## Footnote *Radiometric dating* can't date fossils **directly** since they lack radioactive isotopes. However, minerals in surrounding rocks or volcanic ash can be dated to estimate the fossil's age.

Question 49

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

Answer 49

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 50

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

Answer 50

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 51

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

Answer 51

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 52

# True or False: ____ ____ can only be done on **rock samples** that **have not undergone** metamorphism.

Answer 52

Radiometric dating ## 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 53

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

Answer 53

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

Question 54

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

Answer 54

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 55

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

Answer 55

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 56

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

Answer 56

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 57

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

Answer 57

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

Question 58

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

Answer 58

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 59

What is a **closed system**?

Answer 59

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.