4B3 Evidence for the History of the Earth Flashcards
Explore how relative and absolute dating techniques provide evidence for Earth's historical timeline and age.
What is the purpose of relative dating?
To determine the relative order of events in Earth’s history.
Relative dating places geological events in the correct sequence without providing exact dates.
What type of rocks are typically studied using relative dating?
Sedimentary rocks
Sedimentary rocks form in layers, making it easier to establish the relative age of each layer.
What does the principle of superposition help establish?
The relative age of rock layers.
The oldest layers are typically found at the bottom, with progressively younger layers above them.
What does the principle of original horizontality state?
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.
True or False:
Superposition applies to all sedimentary and igneous rocks.
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.
What principle states that sedimentary layers extend horizontally until they thin out?
Lateral continuity
This principle allows for the correlation of rock layers across large areas.
Fill in the blank:
Fossils are most commonly found in ________ rocks.
sedimentary
Sedimentary rocks preserve fossils due to their formation process.
What is the principle of fossil succession?
Fossils appear in a specific order within the rock record.
This principle allows geologists to identify and correlate rock layers using fossils.
What is an unconformity?
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.
Fill in the blank:
A/an _________ occurs between two layers of sedimentary rock with a gap in deposition.
disconformity
Disconformities are uncomforities that represent periods of erosion or non-deposition between parallel sedimentary layers.
What is a nonconformity?
It occurs where sedimentary rocks cover eroded igneous or metamorphic rocks.
Nonconformities are a kind of uncomfomity that signify significant geologic time gaps.
What is correlation in geology?
Matching rock layers across different areas.
Geologists use fossils and rock characteristics to establish connections.
True or False:
Index fossils are key for identifying and correlating rock layers.
True
Index fossils are widespread, short-lived, and unique to specific time periods.
Which principle shows faults are younger than the layers they cut?
Cross-cutting relationships
This principle states that a fault or intrusion is younger than the layers it cuts through.
Fill in the blank:
______ fossils are critical for correlating distant rock layers.
Index
These fossils, like trilobites and ammonites, help identify and match rock layers across regions.
What is the principle of inclusions?
Fragments within a rock are older than the rock itself.
Inclusions form when pieces of older rock become embedded in newer rock.
True or False:
Intrusions are always older than the surrounding rock layers.
False
Intrusions are younger as they cut through pre-existing layers.
What principle explains the sequence in folded layers?
Original horizontality
Layers are initially deposited flat, and folding happens later.
What is the significance of a stratigraphic column?
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.
Fill in the blank:
The _____ of a rock layer is determined by its position relative to other layers.
age
Determining the relative age of rocks relies on principles like superposition and cross-cutting.
True or False:
Relative dating provides specific numerical ages for rock layers.
False
Relative dating only establishes the sequence of events, not their exact age.
True or False:
Fossils can be used to directly measure the age of rock layers.
False
Fossils help establish the relative age of rock layers, but not the exact age. Radiometric dating is used for that purpose.
What does absolute dating determine?
The actual age of a rock or fossil.
Absolute dating provides a precise age using methods like radiometric dating.
What is radiometric dating?
A method of dating based on radioactive isotope decay.
Radiometric dating relies on the predictable rate of decay of radioactive isotopes in minerals.
Fill in the blank:
Radiometric dating uses _______ to measure isotope decay rates.
half-life
Half-life is the time required for half of a radioactive isotope to decay, a key concept in radiometric dating.
True or False:
An isotope’s half-life changes with temperature or pressure.
False
The half-life of an isotope is constant and is unaffected by environmental conditions like temperature or pressure.
Which isotope is commonly used to date rocks older than 100,000 years?
Uranium-238
Uranium-238 decays to lead-206 and is commonly used for dating rocks millions to billions of years old.
What is the parent isotope in radiometric dating?
The radioactive isotope that decays into a stable daughter isotope.
The parent isotope undergoes radioactive decay to form a stable daughter isotope, which helps determine the age of a sample.
Fill in the blank:
Carbon-14 dating is primarily used for dating _______ materials.
organic
Carbon-14 dating is effective for dating organic materials like wood, bone, and cloth, typically up to 50,000 years old.
True or False:
Carbon-14 can be used to date rocks older than 100,000 years.
False
Carbon-14 dating is only effective for relatively recent fossils or materials (up to about 50,000 years).
Which rock type is most commonly used for radiometric dating?
Igneous rocks
Igneous rocks are formed from the cooling of molten magma, trapping radioactive isotopes in minerals.
What is the age of the Earth according to radiometric dating?
Approximately 4.54 billion years.
Radiometric dating of the oldest rocks and meteorites has provided a consistent age for the Earth of about 4.54 billion years.
What is an example of an isotope used for dating very old rocks?
Potassium-40
Potassium-40 decays to Argon-40 and is used to date rocks older than 100,000 years, especially volcanic rocks.
True or False:
Radiometric dating is the only method used to determine the age of rocks.
False
While radiometric dating is a widely used and accurate method, other methods like stratigraphy are also used in conjunction.
Fill in the blank:
The parent-to-daughter isotope ratio helps determine the _____ of a sample.
age
By measuring the ratio of parent to daughter isotopes, scientists can calculate the age of the sample with high precision.
Which element’s isotopes are used for dating very old meteorites?
Uranium
Uranium isotopes, such as Uranium-238, are used for dating meteorites and rocks as old as the solar system.
What does radiometric dating rely on for accurate results?
The constant rate of decay of isotopes.
The rate at which isotopes decay (half-life) remains constant, providing a reliable means to measure age.
How is the age of the sample calculated in radiometric dating?
By measuring the ratio of parent to daughter isotopes.
The ratio provides the time elapsed since the rock or mineral crystallized, allowing the age to be calculated.
Fill in the blank:
________ ______ is an important method for dating ancient igneous rocks.
Potassium-argon dating
Potassium-argon dating is effective for dating ancient igneous rocks, as potassium-40 decays into argon-40 over time.
True or False:
Radiometric dating can only be used on rocks and not fossils.
False
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.
What is the main advantage of radiometric dating?
It provides precise and accurate numerical ages.
Radiometric dating offers a reliable, exact age, unlike relative dating, which only determines the sequence of events.
What is an example of a radioactive isotope with a short half-life?
Carbon-14
Carbon-14 has a short half-life of about 5,730 years, making it suitable for dating relatively recent organic material.
True or False:
Radiometric dating can only be performed on rock samples that have not undergone metamorphism.
True
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.
What does the presence of daughter isotopes in a sample indicate?
That some time has passed since the rock or mineral crystallized.
The daughter isotopes accumulate over time, and their presence allows scientists to calculate the age of the sample.
What types of radiation can be emitted during isotope decay?
- Alpha radiation
- Beta radiation
- Gamma radiation
These types of radiation are emitted as the parent isotopes decay to form stable daughter isotopes.
True or False:
Radiometric dating can be used to directly date sedimentary rocks.
False
Radiometric dating is typically used on igneous and metamorphic rocks. Sedimentary rocks are dated indirectly using the ages of the layers around them.
What does a stable isotope state mean in radiometric dating?
The isotope has fully decayed into a non-radioactive element.
Once an isotope decays into a stable daughter isotope, the radioactive decay process is complete, allowing scientists to calculate the age of the material.
What is a closed system?
A system where no isotopes are added or lost over time.
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.
