Relative Age
What does relative age mean?
The age of a rock or geologic feature compared with other rocks or features.
What is an unconformity?
A surface where rock has eroded away, creating a break or gap in the rock record.
What does correlation mean in geology?
Matching rocks and fossils from separate locations.
What is an atom?
The smallest part of an element that has all the properties of that element.
What is radioactive decay?
The process in which an unstable element naturally changes into another stable element.
What is the principle of superposition?
In undisturbed rock layers, the oldest rocks are on the bottom.
What type of unconformity has younger sedimentary layers on top of older horizontal sedimentary layers that have been eroded?
Disconformity.
What is an index fossil?
A fossil from a species that existed for a short time, was abundant, and lived in many locations.
What are the three particles found in an atom?
Protons, neutrons, and electrons.
What is a parent isotope?
The unstable isotope that decays.
What does the principle of Original Horizontality state?
Most rock-forming materials are deposited in horizontal layers.
What type of unconformity occurs when younger sedimentary layers are deposited on tilted or folded sedimentary layers?
Angular unconformity.
What three things can scientists use to correlate rock formations?
Rock type, structure, and fossil evidence.
Where are protons and neutrons located?
In the nucleus.
What is a daughter isotope?
The new element that forms when the parent isotope decays.
What does Lateral Continuity tell us about sedimentary layers?
Sediments are deposited in large, continuous sheets.
What type of unconformity occurs when younger sedimentary rocks are deposited on older igneous or metamorphic rocks?
Nonconformity.
If the same index fossil is found in two different rock layers, what can scientists infer?
The rock layers are likely to be a similar age.
What are isotopes?
Atoms of the same element that have different numbers of neutrons.
What is a half-life?
The time required for half of the parent isotopes to decay into daughter isotopes.
Which principle states that a rock containing pieces of another rock is younger than the pieces inside it?
The principle of inclusions.
Why do unconformities create gaps in the rock record?
Because rock has been eroded away before new rock layers were deposited.
Why are index fossils useful when comparing rocks on different continents?
They can help scientists determine whether rock layers in different locations are about the same age.
What is the difference between a stable isotope and a radioactive isotope?
Stable isotopes do not change under normal conditions, while radioactive isotopes are unstable and decay over time.
After two half-lives, what percentage of the original parent isotopes remains?
25%