Chapter 17 - Geologic Time - Concepts and Principles

Question 1

What were absolute ages based on?

Answer 1

Radiometric dating

Question 2

What is the oldest pieice of earth ever found, how old is it?

Answer 2

Zircon crystal, 4.4 Billion years old

Question 3

How old is the oldest known rock on earth? Where was it found?

Answer 3

4.28 billion years, Quebec nuwagituq

Question 4

When were humans created? First fossil evidence of human ancestors?

Answer 4

1.6 million years, Tertiary period, Cenozoic era, Phanerozoic eon

Question 5

When were dinosaurs extinct?

Answer 5

66 million years ago, transition of the mesozoic to cenozoic era

Question 6

Name eon’s and dates

Answer 6

Precambrian, 4.6 By-545My, Cambrian 545M.y to CURRENT

Question 7

Name Era’s and dates for important ones pls

Answer 7

PRECAMBRIAN: hadean, archean, proterozoic
PHANEROZOIC
paleozoic (started 545m.y ago) - mesozoic - cenozoic (CURRENT, started 66m.y ago)

Question 8

When did the first ice age begin?

Answer 8

1.6 MY AGO same time as first fossil of human species

Question 9

What can you say about the periods?

Answer 9

Not equal in length

Question 10

History of dating earth

Answer 10

Bible said 6k years ago

Gelogical field work began, they started measuring rates of sedimentation, how fast does a glacier move

Question 11

Relative dating, how does it work?

Answer 11

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.

Question 12

What is the principle of sedimentary horizontalality

Answer 12

if you deposit a clastic material, most likely it will deposit horizontally

Question 13

Principle of statigraphic superpostion, what is it

Answer 13

When you have horizontally layered things, the things on top are younger than things on bottom
-relative ages

Question 14

Explain horizontal bedding/folding/anticline/syncline

Answer 14

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

Question 15

define anticline, syncline

Answer 15

anticline :Starta slopes downwards, makes an n shape

syncline: opposite, strata slopes upwards, manes a u

Question 16

Define crossbedding

Answer 16

layering within a stratum and at an angle to the main bedding plane

Question 17

What aare ichnofossils used for?

Answer 17

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

Question 18

What are geopetals used for?

Answer 18

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)

Question 19

3 Types of unconformities

Answer 19

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

Question 20

What are cross cutting relationships in relative dating

Answer 20

anything that is cutting must be younger than what is being cut (dikes are cross cutting)

Question 21

define dike

Answer 21

vertical rock between older layers of rock, a geological body which cuts accross

Question 22

What is contact metamorphism in relative dating

Answer 22

When a body of magma alters the surrounding country rock. So like magma makes the contact point to make metamorphasis youlo

Question 23

What is lithostratigraphic correlation

Answer 23

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

Question 24

How does volcanic ash aid in lithostratigraphic correlation (any relative dating)

Answer 24

• 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

Question 25

Compare biostratigraphy correlation | with lithostratographic correlation

Answer 25

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

Question 26

What is biostratigraphy correlation

Answer 26

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,

Question 27

What is an index fossil

Answer 27

-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

Question 28

Coloradeu plateau? what is it?

Answer 28

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

Question 29

define isotope

Answer 29

Atom of an element with a specific number of protons and electrons

Question 30

Define natural radioactivity

Answer 30

isotopic changes via spontaneous emission of particles or radiation

Question 31

what is radioactivity

Answer 31

when unstable nuclei spontaneously decay

Question 32

3 types of radioactive decay

Answer 32

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)

Question 33

Age equation of radioactive decay

Answer 33

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))

Question 34

What is half life? Is it linear?

Answer 34

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

Question 35

Methods of dating

Answer 35

Relatively crude sample, 150$, very accurate OR -microbeam -- more expensive -extremely high spatial resolution,high accuracy, 500$

Question 36

``` Common half lifes: Carbon 14 daughter? Half life? Effective dating range? Minerals that can be dated? (this is all wrt carbon 14) ```

Answer 36

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

Question 37

Applications of dating: | dating of igneous rocks

Answer 37

BREAK THERES NO ANSWER JUST REMEMBER AN APLICATION OF DATING IS DATING IGNEOUS ROCK

Question 38

Applications of dating: | dating of metamorphic rocks

Answer 38

heat it up, reset the clock to age of sample

Question 39

Applications of dating: | dating of fossils and sedimentary rocks

Answer 39

can date fossils, old or young, could just use radiation that comes out of sample

Question 40

Applications of dating: | dating of artifacts

Answer 40

NO ANSWER JUST REMEMBER artifact dating is an application

Question 41

Applications of dating: | dating of geologic sequences

Answer 41

instead of using relative dating, we just use radiation that comes out of sample to get the exact time span

Question 42

Applications of dating: | calibration of geologic time

Answer 42

put number on boundaries based on dating of ash layers to put a time between periods

Question 43

Applications of dating: | reconstructing earth through time

Answer 43

looking at things like pole wandering, where continents were, date the magnetic strips to determine where the poles were at certain time periods

Question 44

Applications of dating: | reconstructing life through time

Answer 44

what organisms were living at what time periods