Class Notes- Unit 4 Flashcards
What are the 3 Geological times?
1) Relative Time
2) Absolute Time
3) gEological Time scale
What is dating?
the procedures we use to:
i. determine when an event took place, and
ii. determine the sequence of events
What is the age of a rock?
the time it was emplaced
What is relative geological time?
the sequence of processes that have occurred at location.
How can we work out relative geological time?
WE can see this with the naked eye–or work it out with fairly simple geological observations.
What are the 5 geological observations we can use to determine relative time?
- superposition
- intrusion
- deformation
- unconformity
- fossil correlation
What did our understanding of relative time begin with
Nicolaus Steno ~ 1660
What is the law of superposition?
younger rock layers are deposited on top of older rock layers (stratigraphic succession)
What is stratum?
1 layer
What is strata?
several layers
What is the principle of original horizontality
Noticed that rock layers were largely horizontal
What is intrusion?
intrusions in rock strata (the intrusion is younger than the rock it cuts) from magma…volcano is optional
Deposition___erosion
folding
Deposition___erosion
faulting
What creates earthquakes?
faulting
Anticline and syncline are included in which geological observation?
unconformity
What are 4 types of unconformity?
1) angular unconformity
2) disconformity
3) paraconformtiy
4) nonconformity
What is angular unconformity?
buried topographic surface
*An angular unconformity is an unconformity where horizontally parallel strata of sedimentary rock are deposited on tilted and eroded layers, producing an angular discordance with the overlying horizontal layers.- via wikipedia
Which unconformity includes “hiatus”?
angular unconformity
What is hiatus?
apparent time erosion took place
What is a disconformity?
A disconformity is an unconformity between parallel layers of rock which represents a period of erosion or non-deposition. - via wikipedia
What is paraconformity?
- no strata
- ‘time gap’ or ‘rock gap’
- missing erosion
- [no strata deposited, no erosion]
- Rocks underneath not folded, tilted, faulted, etc.
- Erosion has not taken place
- Just a long time with no deposition
- Process just left no rocks but no real ‘time gap’
What is the most significant type of unconformity?
angular unconformity
What is the most common type of unconformity?
paraconformity
What is nonconformity?
Non-volcanic rocks rest on crystalline rocks
What begins the process of nonconformity?
Magma intrudes original strata
What is contact metamorphism? What is regional metamorphism?
Contact metamorphism: modification by heat
Regional metamorphism: modification by heat if rocks are buried deeply
What is fossil range?
every organism exist for a range of time–time span an organism lives.
How long, on average, is the fossil range for various species?
6 million years (6 my)
What does the fact that fossil range overlaps allow for?
more precise relative dating
Where do local gaps in the fossil cord compared with more regional or global result?
unconformities
Fossils, like living organisms, have specific___ranges.
geographic
How do fossils replace one another?
In a definite, though complex, manner – on both local and global scales (because of time ranges and environmental conditions)
What are index fossils?
Fossils with a “short” time range, but which are broadly geographically distributed are especially useful.
When did trilobites live from?
526-250 myo
When did clams live for?
500-450 myo - present
when did ginkgo live from?
270 - 0 may
When did dinosaurs live for?
220 - 65 myo
When was the largest extinction/
at end of paleozoic (250)
What percent species became extinct at the end of paleozoic?
90%
What percent of species when extinct at end of mesozoic?
70%
When give dinosaurs go extinct?
65 myo
What are the eons from oldest to youngest?
Oldest: Hadean
Archean
Proterozoic
Youngest: Phanerozoic
What are the eras of the phanerozoic eon (from oldest to youngest)
Oldest: paleozoic
Mesozoic
Youngest: Ceonozoic
What were the major events of the Hadean eon?
- Birth of the earth and Solar System
- Most asteroid impacts took place on moon–moon formed as well
- Iron catastrophe (differentiation)
When were the first life forms?
archean
What are the 3 eons of the Precambrian?
Hadean
Archean
Proterozoic
How many mya was Hadean?
4550
How many mya was Archean?
3800
How many mya was Proterozoic?
2500
How many mya was Paleozoic?
250
How many mya was Mesozoic?
65
How many mya was Cenozoic?
0
How many mya was the Phanerozoic?
542
When were the 4 major extinctions?
~ 450 (Paleozoic)
~ 350 (Paleozoic)
~ 250 (Palaeozoic) (most significant)
~ 65 (Mesozoic)
