Geologic time/Dating Flashcards
What is a half-life?
A half-life is the amount of time it takes half of the parents(unstable) to become daughters(stable).
What are the three types of unconformities called?
Disconformity, nonconformity, and angular unconformity.
What is an angular unconformity?
An angular conformity is when horizontal rocks are deformed, and then more rock builds on top of it.
What is a disconformity?
A disconformity is when the top rock layer gets eroded, and then more rock builds on top of it
What is a nonconformity?
A nonconformity occurs when sedimentary rock gets eroded to expose metamorphic or igneous rock, and then new rock develops on top of it.
How does C-14 work?
C-14 is used to date fossils. Scientists compare C-14 and C-12 in a bone. However, correction curves are needed due to changes in the atmosphere that can effect C-14 concentrate.
How do you use a varve sequence to date a rock?
A varve sequence is a core found in glacial lakes. There is a layer of mud representing winter and a layer of sand representing summer. Using those layers, you can determine a rocks age, if it is recent.
What is alpha decay?
Alpha decay is when 2 protons and 2 neutrons are released as alpha particles.
What is beta decay?
Beta decay is when a neutron releases it’s electron and becomes a proton.
Name the eons in descending age?
Hadean, archean, proterozoic, phanerozoic.
HAPP(Y)
What does hadean mean?
It means molten
What is special about the archean eon?
The oldest rock is found then, the ocean and atmosphere developed.
What does proterozoic mean?
Early life
Name the eras in descending age
Precambrian, paleozoic, mesozoic, cenozoic
What does paleozoic mean?
Old life
What does mesozoic mean?
Middle life
What does cenozoic mean?
Recent life
What is the mnemonic device for the periods?
Come Over Some Day, Maybe Play Poker, Three Jacks Kill Two Queens.
Name the periods in descending age
Cambrian, ordovician, silurian, devonian, mississippian, pennsylvanian, permian, triassic, jurassic, cretaceous, tertiary (paleogene and neogene), quaternary
Name the epochs in descending age
Paleocene, eocene, oligocene, miocene, pliocene, pleistocene, holocene.
What is the mnemonic device for the epochs
Pretty Eager Old Men Play Poker Hard (PEOMPPH)
What period(s) is the age of invertebrates?
Cambrian and Ordovician
What period(s) is the age of fish?
Silurian and Devonian
What periods are the age of amphibians?
Carboniferous and Permian
What periods are the age of reptiles?
Triassic, Jurassic, and Cretaceous (Mesozoic era)
What periods are the age of mammals?
Tertiary, Quaternary (Cenozoic era)
When did the ice age cycles start?
2.6 million years ago
When was there a meteor impact(dinosaurs died)?
66 million years ago
When did pangaea form?
252 million years ago
When was the explosion of life?
541 million years ago
When did Earth form?
4.6 billion years ago
How does the geologic time scale break down?
Eon-era-period-epoch
What are the relative age dating rules?
Original horizontality, superposition, lateral continuity, cross-cutting relationships, inclusions, faunal succession
What is faunal succession?
Using index fossils to relatively date rocks.
What is the rule of inclusions?
Inclusions are older than the rock that contains them.
What are cross-cutting relationships?
The intrusion is younger than the rock they intrude.
What is lateral continuity?
Sedimentary layers continue horizontally over a distance.
What is superposition?
The oldest sedimentary layers are on the bottom.
What is original horizontality?
Sedimentary layers form horizontally. Any deformations happen after the rock forms.
What is the difference between relative and absolute
age dating?
In relative age dating, you establish a series of events to figure out age compared to other rocks. In absolute age dating, you figure a numerical value for the rock’s age. You cannot absolutely date sedimentary rocks.
How do you figure out how many half-lives have passed?
You use the ratio of parent to daughter and use the fact that the parent decreases by 50% every time.
How do you figure out the age of a rock using half-lives?
Once you know how many half-lives have passed in an isotope, you have to multiply that by the half-life time of that isotope.
