Chapter 17 - Geologic Time - Concepts and Principles Flashcards
What were absolute ages based on?
Radiometric dating
What is the oldest pieice of earth ever found, how old is it?
Zircon crystal, 4.4 Billion years old
How old is the oldest known rock on earth? Where was it found?
4.28 billion years, Quebec nuwagituq
When were humans created? First fossil evidence of human ancestors?
1.6 million years, Tertiary period, Cenozoic era, Phanerozoic eon
When were dinosaurs extinct?
66 million years ago, transition of the mesozoic to cenozoic era
Name eon’s and dates
Precambrian, 4.6 By-545My, Cambrian 545M.y to CURRENT
Name Era’s and dates for important ones pls
PRECAMBRIAN: hadean, archean, proterozoic
PHANEROZOIC
paleozoic (started 545m.y ago) - mesozoic - cenozoic (CURRENT, started 66m.y ago)
When did the first ice age begin?
1.6 MY AGO same time as first fossil of human species
What can you say about the periods?
Not equal in length
History of dating earth
Bible said 6k years ago
Gelogical field work began, they started measuring rates of sedimentation, how fast does a glacier move
Relative dating, how does it work?
Judghing who is older than who, you know who is older, but you dont know the exact age. Yu can tell a general range, but not exact, just relative to.
What is the principle of sedimentary horizontalality
if you deposit a clastic material, most likely it will deposit horizontally
Principle of statigraphic superpostion, what is it
When you have horizontally layered things, the things on top are younger than things on bottom
-relative ages
Explain horizontal bedding/folding/anticline/syncline
for horizontal bedding, stuff on top is older
but when we see syncline anticline, we could have 3 sections, but the top and bottom one are the same time period due to synclines and anticlines, thus the principle of superposition only works if you understand where you are, where are the folds, some of the rocks could be upside down
define anticline, syncline
anticline :Starta slopes downwards, makes an n shape
syncline: opposite, strata slopes upwards, manes a u
Define crossbedding
layering within a stratum and at an angle to the main bedding plane
What aare ichnofossils used for?
Ichnofossils were used as trace fossils to aid in relative dating (it could be a footprint, feeding trails…)
-HELPS US DETERMINE WHATS UP OR DOWN
What are geopetals used for?
TEll us whats up or whats down when relative dating(make a thin section of the rock, look at it, thats what tells u info)
3 Types of unconformities
Disconformity - wavy line, b/c bedding above and below should be paralel
Angular conformity - angle between bedding and unconformity surface
Nonconformity
-u have an unconformity, and 1 side of the unconformity doesnt have bedding
how do you tell if its an unconformity? there will be rock surrounded by material, the rock that is surronded by material is older, the rock surrounding the boulder is younger
What are cross cutting relationships in relative dating
anything that is cutting must be younger than what is being cut (dikes are cross cutting)
define dike
vertical rock between older layers of rock, a geological body which cuts accross
What is contact metamorphism in relative dating
When a body of magma alters the surrounding country rock. So like magma makes the contact point to make metamorphasis youlo
What is lithostratigraphic correlation
In areas of adequate exposures, rock units can be traced laterally, even if occasional gaps exist, and correlated on the basis of similarity in rock type and position in a sequence
- so just looking at the rock bedding of earths crust in surround geological area, the bedding will be around the same
- ash layers/volcanic ash are very good to tell us the relative time b/c it will be over the same area it occured
How does volcanic ash aid in lithostratigraphic correlation (any relative dating)
- ash layers/volcanic ash are very good to tell us the relative time b/c it will be over the whole area that it occured
- volcanin eruption doesnt give a shit if its a lake or a mountain, will be the same everywhere, kind of gives us a base point
- the are known as chrono-stragographic markers
Compare biostratigraphy correlation
with lithostratographic correlation
biostratigraphy is better than lithostratohgraphic correlation b/c bio is looking at fossils, so its over a much larger area than just looking over the bedding of one region
What is biostratigraphy correlation
looking at fossils
-this region has this kind of fossils, the same fossil occurs over here, but in area A, the fossils are found in the one bed, while the same fossil in area B is in 2 Layers,
What is an index fossil
-if a species has a short lifespan (say gets extinct after 10m.y), then we can use them to relatively date everything that includes them, and they will have
occured at around that timespan
-if species lived for a very long time, it isnt an index fossil
Coloradeu plateau? what is it?
Place to see the 3 national parks in US
- it is large platform with little tectonic activity,
- grand canyon oldest rocks about 2b.y old
- lots of angular conformities in grand canyon, which is also max 2600m deep
define isotope
Atom of an element with a specific number of protons and electrons
Define natural radioactivity
isotopic changes via spontaneous emission of particles or radiation
what is radioactivity
when unstable nuclei spontaneously decay
3 types of radioactive decay
1) Alpha decay, in which unstable parent nucleus emits 2 protons and 2 neutrons
b) Beta decay - electron emmited from nucleus
c) Electron capture - proton captures an electron and is converted to a neutron (which is 1 proton 1 electron)
Age equation of radioactive decay
T - age of sample
D - Number of atoms of daughter isotope in sample
P - number of atoms in parent isotope
Lambda - decay constant of parent isotope, equal to inverse of radioactive half life of parent isotope times ln(2)
D=P/(e^(lambda*t))
What is half life? Is it linear?
Each half life represents the time it takes for half of parent element to decay to daughter element
-not linear, curve looks like y=1/x, cuz first half life is a lot of stuff being decayed, second is less stuff, horizontal asymptote, never reaches 0
Methods of dating
Relatively crude sample, 150$, very accurate
OR
-microbeam – more expensive
-extremely high spatial resolution,high accuracy, 500$
Common half lifes: Carbon 14 daughter? Half life? Effective dating range? Minerals that can be dated? (this is all wrt carbon 14)
carbon 14: daugher is nitrogen 14, half life 5730 yrs, effective dating range 0-100k years, minerals and rocks that can be dated: plants (coal) bone, shells
Applications of dating:
dating of igneous rocks
BREAK THERES NO ANSWER JUST REMEMBER AN APLICATION OF DATING IS DATING IGNEOUS ROCK
Applications of dating:
dating of metamorphic rocks
heat it up, reset the clock to age of sample
Applications of dating:
dating of fossils and sedimentary rocks
can date fossils, old or young, could just use radiation that comes out of sample
Applications of dating:
dating of artifacts
NO ANSWER JUST REMEMBER artifact dating is an application
Applications of dating:
dating of geologic sequences
instead of using relative dating, we just use radiation that comes out of sample to get the exact time span
Applications of dating:
calibration of geologic time
put number on boundaries based on dating of ash layers to put a time between periods
Applications of dating:
reconstructing earth through time
looking at things like pole wandering, where continents were, date the magnetic strips to determine where the poles were at certain time periods
Applications of dating:
reconstructing life through time
what organisms were living at what time periods
