Lab 9

Question 1

What are the 5 principles of Stratigraphy

Answer 1

Principle of Superposition
Principle of Original Horizontality
Principle of Cross-Cutting relations
Principle of Inclusions
Principle of Fossil Succession

Question 2

Describe the Principle of Superposition

Answer 2

In an undisturbed sequence of rocks, the oldest rocks are at the bottom and the youngest at the top. If it is found to be the reverse, the sequence must have been overturned at some point

Question 3

Describe the principle of Cross-Cutting Relations

Answer 3

If a rock unit is cross-cut by another feature such as a fault or igneous intrusion, the feature that cuts across is younger than the rock unit which is dissected

Question 4

Describe the Principle of Original Horizontality

Answer 4

All waterline sediments were deposited horizontally (or nearly so). If sedimentary rocks are found tilted or overturned, this was due to a later event. This principle only determines the relative time of the tilting event (often the tilting is due to the beds being part of large scale folds)

Question 5

Describe the principle of Inclusions

Answer 5

When a rock unit contains fragments of another rock within it, those fragments represent a rock that is older than the rock around them.

Question 6

Describe the principle of fossil succession

Answer 6

Fossil species follow each other in the rock record in a recognizable and irreversible order. Thus we can use this information to correlate strata over large distances, despite differences in rock type of geologic processes.

Question 7

What are unconformities

Answer 7

Much of geologic time in a given region is not included in the rock record. Theses are times in which the erosion was occurring rather than deposition. We would expect to see rocks of a certain age, but don’t. What we do see is an erosional surface of older rock overlain by younger sediments called an unconformity.

Question 8

What are the 3 main types of unconformity

Answer 8

Angular unconformity
Disconformity
Nonconformity

Question 9

What is an Angular Unconformity

Answer 9

An erosional surface between older layers which have been uplifted and tilted prior to erosion, and younger layers. A different dip angle between the overlying and underlying beds results.

Question 10

What is a disconformity

Answer 10

The older, eroded surface is made of sedimentary layers which have the same orientation as the overlying beds. This type is the most difficult to see in the field and requires a thorough knowledge of local geology, often based on missing fossil sequence.

Question 11

What is a nonconformity

Answer 11

Older, eroded surface is a crystalline rock which is subsequently overlain by sediments. Only contacts between igneous rocks and overlying rocks that are erosional are nonconformities.

Question 12

What are radioactive isotopes

Answer 12

Radioactive isotopes are elements in minerals that are able to tell us how much time has elapsed since the rock was formed. This is because radioactive isotopes are unstable and decay or break down at predictable rates.

Question 13

What is an isotope

Answer 13

An isotope is one of several forms of one element, all having the same number of protons in the nucleus, but differing in the number of neutrons

Question 14

What is Radiometric dating

Answer 14

Radiometric dating is possible because radioactive atoms of some elements are incorporated into the crystal lattice of minerals at the time of their formation. Over time these parent atoms decay and their daughter elements are trapped within the mineral.

Question 15

What level does radioactive decay occur on

Answer 15

Radioactive decay occurs on the atomic level as particles in the nucleus disintegrate, changing the atom into one of a different element and emitting radiation in the process.

Question 16

What is a half life

Answer 16

The half life is the time it takes half a sample of a radioactive isotope to decay. Constant no matter the amount of the isotope. So the time it takes to go from 100% to 50%, is equal to the time it takes to go from 50% to 25%.

Question 17

What is decay curve

Answer 17

A decay curve is a simple graph that represents the amount of parent isotope we would expect to find remaining in a mineral or rock after a given period of time has passed.

Question 18

What formula gives the percentage of parent atoms remaining after time n

Answer 18

2^-n

Question 19

What is the detection limit for most radioactive elements

Answer 19

The detection limit for most radioactive elements rarely exceeds five half lives

Question 20

What is the decay of U238

Answer 20

U238 -> Pb206
HL = 4.56 BY
Found in Zircons (in granites) and uranitite

Question 21

What is the decay of U235

Answer 21

U235 -> Pb207
HL = 704 MY
found in Zircons (in granites), and uranitite

Question 22

What is the decay of K40

Answer 22

K40-> Ar40 and Ca40
HL = 1.251 BY
Found in muscovite, biotite, hornblende, K-feldspar, glauconite, volcanic rock

Question 23

What is the decay of Rb87

Answer 23

Rb87->Sr87
HL = 48.8 BY
Found in K-mica, K-felspar, Biotite, metamorphic rocks

Question 24

What is the decay of Th230

Answer 24

Th230->Pb206
HL = 75 KY
Found in Oceanic Sediments

Question 25

What is the decay of Th232

Answer 25

Th232-> Pb208 HL = 13.9 BY Found in Zircon, Uranitite

Question 26

What is the decay of C14

Answer 26

C14 -> N14 HL = 5,730 Yrs Found in wood, bone, shells

Question 27

What are some other dating methods

Answer 27

Tree-rings, valves, and ice layers are also ways of determining the absolute age of past events.

Question 28

What is Palaeontology

Answer 28

the study of prehistoric animals and plants whose remains are found in sedimentary rocks and described in fossils. To be considered a fossil, all or part of the actual organisms or some trace of its activity must be preserved in the rock

Question 29

What are the Eons of geologic time

Answer 29

Archean (4.7-2.5 BY) Proterozoic (2500-545 MY) (Archean + Proterozoic = Cryptozoic = Hidden life) Phanerozoic (545 MYA - Present) = visible Life

Question 30

What are the Eras of the Phaneroozic

Answer 30

Paleozoic (age of invertebrates) 545-245 MY Mesozoic (Age of reptiles) 245-66 MY Cenozoic (Age of mammals) 66-0 MY

Question 31

What are the Periods of the Paleozoic

Answer 31

Cambrian 545-505 MY Ordovician 505-438 MY Silurian 438-408 MY Devonia 408-360 Carboniferous (360-286) (contains the Mississippian (360-320 MY) and Pennsylvanian (230-286 MY)) Permian 286-245 MY

Question 32

What are the Periods of the Mesozoic

Answer 32

Triassic 245-208 MY Jurassic 208-144 MY Cretaceous 144-66 MY

Question 33

What are the Periods of the Cenozoic

Answer 33

Paleogene 66-24 My Neogene 24-1.6 My (Paleogene + Neogene used to equal the Tertiary) Quaternary 1.6-0 My

Question 34

What are the Epochs of the Paleogene

Answer 34

Paleocene 66-57 MY Eocene 57-37 My Oligocene 37-24 My

Question 35

What are the Epochs of the Neogene

Answer 35

Miocene 24-5.3 My Pliocene 5.3-1.6 My

Question 36

What are the Epochs o f the Quaternary

Answer 36

Pleistocene 1.6-0.01 My Recent 0.01-0 My