Relative Dating
A scientist wants to know whether one rock is older or younger than another rock, but does not need an exact numerical age. What type of dating should be used?
Relative dating
A fossil is found in several rock layers and is useful for comparing the relative ages of those layers. What kind of fossil is this?
Index fossil
A radioactive isotope takes a certain amount of time for half of the parent atoms in a sample to decay. What is this amount of time called?
Half-life
Scientists organize Earth's very long history into divisions so that major events and changes can be studied more easily. What system do they use?
Geologic Time Scale
A sedimentary rock layer is found below another undisturbed layer. Without knowing their exact ages, what can you conclude about the two layers?
The lower layer is older than the upper layer.
In an undisturbed stack of sedimentary rocks, which layer would generally be the oldest—the bottom layer or the top layer? What principle supports your answer?
Principle of Superposition
Part of the rock record is missing because rocks were eroded or sediments were not deposited. What geologic feature does this represent?
Unconformity
An unstable parent isotope changes into a more stable daughter product over time. What process is taking place?
Radioactive decay
In the Geologic Time Scale, what is the largest division of geologic time?
Eon
A rock contains fragments of another rock inside it. Which rock is older—the fragments or the rock surrounding them? What principle supports your answer?
The fragments are older; Principle of Inclusions.
Sediments are deposited in layers that are generally horizontal. Which principle explains this arrangement?
Principle of Original Horizontality
Scientists find the same index fossil in two rock layers from different locations. What does this evidence suggest about the ages of the two layers?
The two rock layers are likely the same or similar in relative age.
A radioactive sample has only 50% of its original parent isotope remaining. How many half-lives have passed?
1
Give the correct arrangement of divisions from largest to smallest
Eon → Era → Period → Epoch
Two rock layers in different locations contain the same index fossil. What can scientists infer about the relative ages of the two rock layers?
The rock layers are likely the same or similar in relative age.
An igneous intrusion cuts across several existing rock layers. Which principle tells us that the intrusion is younger than the layers it cuts?
Principle of Cross-Cutting Relationships
A scientist needs to determine the numerical age of a rock rather than simply whether it is older or younger than another rock. Which dating method would be appropriate?
Absolute dating
A radioactive mineral originally contained 160 grams of a parent isotope. After some time, only 20 grams of the parent isotope remain. How many half-lives have passed?
3
Jurassic is one of the divisions used in the Geologic Time Scale. Is it an Eon, Era, Period, or Epoch?
Period
A radioactive sample has 12.5% of its original parent isotope remaining. If its half-life is 8,000 years, how old is the sample?
24,000 years
A sandstone contains pieces of an older rock. Which principle explains why those rock fragments must be older than the sandstone containing them?
Principle of Inclusions
A geologist compares two rock layers and determines that one formed before the other, but does not give an exact age in years. What type of dating is being used?
Relative dating
A radioactive isotope has a half-life of 10,000 years. A rock sample contains only 12.5% of its original parent isotope. Approximately how old is the rock?
30,000 years
The Holocene is a division of geologic time. Is it an Eon, Era, Period, or Epoch?
Epoch
An igneous intrusion cuts through three sedimentary rock layers. Later, erosion removes part of the upper layers, creating a gap in the rock record. Which principle determines the age of the intrusion, and what geologic feature represents the missing rock record?
Principle of Cross-Cutting Relationships; Unconformity.