CHPTR 8 Geological Time Flashcards
principals of relative dating (7)
- superposition
- original horizontality
- lateral continuity
- cross-cutting relationships
- inclusions
- contact metamorphism
- fossil succession
Nicolas Steno
Discovered
superposition
original horizontality
lateral continuity
for relative dating of rocks
uniformitarianism
if we see a geological process today and we see evidence of it in the past; they’re probably the same thing
principal of superposition
in a sequence of undeformed sedimentary rocks, each layer is older than the one above and younger than the one below
original horontality
most rocks form at a horizontal angle
if rocks are tilted, it is because something happened between deposition and now
lateral continuity
if a layer of sediment initially extends latarallly in all directions but is now separated by an erosional feature it can be assumed that it was originally continuous
cross cutting relationships
intrusions are younger than the rocks they intrude
a fault is younger than the rock that it has fractured
principal of inclusions
a layer containing an inclusions is younger that the inclusion
unconformity represents?
“lost time”
nonconformity
boundary between sedimentary and igneous contact - causes inclusions
angular unconformity
angled/horizontal boundary between sedimentary layers
disconformity
horizontal/horizontal boundary between sedimentary layers
principal of contact metamorphism
metamorphism has to occur after the rock has formed
William Smtih
produced first geological map using fossil succession
index fossils
fossils that are present in a wide geographic range and a short time span
John Joly + how old he thought the Earth was
studied amount of salt in ocean + compared it to the rate that salt enters the ocean from rivers to determine the age of the Earth
99 million
(this was a minimum)
Lord Kelvin + how old he thought the Earth was
estimated the rate at which a sphered would cool by conduction of heat
20 - 400 million
what was Lord Kelvin’s mistake (2)
- heat is transported by convection and conduction in the Earth
- radioactive decay generates heat
half life
time it takes for half the atoms in a sample to decay
alpha particle
2 neutrons, 2 protons
parent atom
atom has not lost an alpha particle yet
daughter atom
atom has lost an alpha particle
When does radioactive dating clock start
when a grain crystallizes from the magma
How do we use radioactivity to date rocks
- crystals form in magma with just parent atoms
- nothing can enter or the leave the crystal grain
- we can check after 1 half life and see that half of the parent atoms have decayed
mass spectrometer (+how we use it to date rocks)
- vaporizes rock sample
- accelerates sample as a beam of ions
- sample is deflected around corner by large magnet
- heavier ions are deflected less
- count the number of ions with different weights (parent vs. daughter)
What happens in terms of radioactive dating if we melt or metamorphosize a rock
the clock “resets”
ie. daughter atoms can escape
What type of rock does radioactive dating work best on
igneous
Order of decreasing geological time scale
Eon - era - period - epoch
Hadean Eon defining features
magma ocean
no signs of life
Archean Eon defining features
- first cratons formed
- evidence of water from zircon grains
- prokaryotes in ocean
- stromatolites with photosynthesis
- no oxygen
why did the Archean eon have no oxygen
all oxygen produced reacted with the large amounts of iron in the ocean to form banded iron
Proterozoic eon defining features
- early life
- cratons join to form continents
- iron is gone from the ocean and oxygen accumulates
- 2 supercontinents joined then later broke up
- ended with the snowball Earth
Proterozoic types of life
early on; eukaryotes developed
by the end; first multicellular plants and animals
Phanerozoic
- visible life
- Pangea supercontinent joined then eventually separated
- 5 major mass extinctions + evolution
- includes paleozoic, mesozoic, cenozoic era
Precambrian eons
Hadean
Archean
Proterozoic
Paleozoic era defining features
- hard shells animals, fish, amphibians, reptiles
- assembly of pangea
- ended with a great mass extinction
Mesozoic era defining features
- mammals and dinosaurs
- pangea begins to break up
- sea levels rise
- end defined by the meteor impact/volcano activity that killed the dinosaurs
cambrian explosion
many species arriving then disappearing during the beginning of the paleozoic era
kt boundary
Cretaceous–Tertiary boundary; iridium rich clay layer (which is evidence of an asteroid impact)
Chicxulub
the asteroid that killed all of the dinosaurs (ended the mesozoic era)
Describe the structure of the Asteroid crator
a crator with a mountain in the centre; due to the Earth rapidly rebounding
evidence for the gulf of Mexico being the asteroid crator
- circular pattern of gravity anomalies
- drilling revealed strange rocks
- seismic data shows a crater
- the age of the impact structure is the same age as the end of the mesozoic era
cenozoic era defining features
- mammals develop without dinosaurs
- Pangea breaks up
- formation of Alps and Himalayas
Quaternary Period
the current ice age;
can be broken into
pleistocene epoch
holocene epoch
pleistocene epoch defining feature
start of ice age until the last retreat
holocene epoch defining features
modern day
- the 6th mass extinction
- interglacial interval
global boundary stratotype section and point (GSSP)
markers to show boundaries between eras
Beginning of the Hadean eon
4567 Ma
End of Hadean eon
4000 Ma
Beginning of Archean eon
4000 Ma
End of Archean eon
2500 Ma
Start of Proterozoic eon
2500 Ma
End of Proterozoic eon
541 Ma
Start of Phanerozoic eon
541 Ma
Start of paleozoic era
541 Ma
End of paleozoic era
250 Ma
start of mesozoic era
250 Ma
end of mesozoic era
65 Ma
Start of cenozoic era
65Ma
Start of Quaternary period
2.6 Ma
Alberta geology from the Quaternary period
thin layer of glacial deposits
some alluvial deposits
soil
Alberta geology from the Phanerozoic eon
- sedimentary rocks of WCSB
- thickens from East to West
- contains hydrocarbons
Alberta geology from the Pre Cambrian eons
- igneous and metamorphic rocks
- crystalline basement
- Archean and Proterozoic aged rocks
WCSB
western canada sedimentary basement
Alberta geology from specifically Hadean
no geological history in Alberta
Alberta geology from specifically Archean
some basement rocks form (cratons)
Alberta geology from specifically Proterozoic
- the rest of basement rocks form
- Archean and Proterozoic cratons join to form North America
Which part of Alberta are Archean rocks found
SE Alberta
Which part of Alberta are Proterozoic rocks found
NW Alberta
Sequence of eons
Hadean, Archean, Proterozoic, Phanerozoic
sequence of eras in phanerozoic eon
paleozoic, mesozoic, cenozoic
which era is quaternary in
cenozoic
which era is neogene in
cenozoic
which era is paleogene in
cenozoic
which era is cretaceous in
mesozoic
which era is jurassic in
mesozoic
which era is triassic in
mesozoic
which era is permian in
paleozoic
which era is pennsylvanian in
paleozoic
which era is mississippian in
paleozoic
which era is devonian in
paleozoic
which era is silurian in
paleozoic
which era is ordivician in
paleozoic
which era is cambrian in
paleozoic
the first period of the paleozoic era
cambrian
