Ch 3: Geological Time

Question 1

Isotopic (radiometric) ages

Answer 1

Dates with numbers (absolute dates). As exact as you can get..

Question 2

Atoms are built from subatomic particles:

Answer 2

Protons, Neutrons, Electrons.

Question 3

Nucleus includes ___ and is surrounded by an ____

Answer 3

Protons and neutrons, electron cloud

Question 4

Electron cloud determiens

Answer 4

chemical properties

Question 5

Neutrons

Answer 5

neutrons help bind nucleus together, the number of neutrons can vary resulting in isotopes

Question 6

Radioactive decay

Answer 6

unstable isotopes break down.
n –> p + e. Loss of 2(n+p).
Emit particles and energy

Question 7

Radioactive decay enables

Answer 7

measurement of geologic time due to its predictable rate of decay. (assuming closed system)

Question 8

Half-Life

Answer 8

Time for half of the parent atoms of an isotope to decay into its daughter. Measures decay rate.

Question 9

Half-Life formula

Answer 9

lamda=ln(2)/t(1/2)

Question 10

Requirements for age determination

Answer 10

half life or decay constant of the isotope, original amount of parent and daughter isotope in the sample, final amount of parent/daughter isotope in the sample, need to know approx. age of sample.

Question 11

Limitations of half-life

Answer 11

mineral grains must have formed at the same time as the rock. Can’t date sedimentary rocks

Question 12

Stratigraphy

Answer 12

relative dating techniques for sedimentary rocks. Uses relative ages of adjacent layers: order of strata, correlation

Question 13

Order of strata

Answer 13

1. Principle of original horizontality

2. Principle of superposition

Question 14

Principle of original horizontality

Answer 14

sedimentary strata are initially horizontal

Question 15

Principle of superposition

Answer 15

in an undisturbed succession, higher rocks are younger.

Question 16

Correlation by Lithology

Answer 16

Compare successions of layers

Question 17

Correlations:

Answer 17

1) Lithology

2) Fossils

Question 18

Correlation by Fossils

Answer 18

Compare similar fossils or fossil assemblages

Question 19

Time scale

Answer 19

• Correlation gives relative timing of strata, was used to develop a geological time scale
• Eras divided into periods
• Subsequently numerical ages were added using isotopic methods

Question 20

Cross-cutting relationships

Answer 20

Shows relative ages of features: igneous intrusive relationships, faults, unconformities, inclusions.

Question 21

Igneous intrusive relationships

Answer 21

intrusion must be younger than host rock. i.e. Magmatic intrusions

Question 22

Faults

Answer 22

faults must be younger than surrounding rocks

Question 23

Unconformities:

Answer 23

Ancient Erosional Surface - Time gap or hiatus: angular unconformity, disconformity, nonconformity

Question 24

Angular unconformity

Answer 24

different orientations above and below

Question 25

Disconformity

Answer 25

Strata have same orientation above and below

Question 26

Nonconformity

Answer 26

Unit below is not sedimentary

Question 27

Earth History

Answer 27

Birth (4.6 Ga) - Hadean (4 Ga) - Archean (2.5-4 Ga) - Proterozoic (543 Ma -2.5 Ga) - Phanerozoic (0- 543 Ma)

Question 28

Hadean Eon

Answer 28

Period before earliest known rocks, heating from radioactive decay melted most of early Earth. Intense meteorite bombardment

Question 29

Archean Eon

Answer 29

Starts with earliest known rocks (Acasta Gneiss). Interior of Earth was hotter than now. Atmopshere mainly CO2, N2. First evidence of life around 3.5Ga.

Question 30

First evidence of Life

Answer 30

Bacteria in the Warrawoona formation in Australia, simple life only

Question 31

Proterozoic Eon

Answer 31

Defined at 2.5Ga. Tectonic system similar to present day. Single-celled organisms became abundant. Increasing oxygen.

Question 32

Life during proterozoic

Answer 32

Mainly soft body organisms, photosynthesis was happening, evolution of a backbone by the end of proterozoic

Question 33

Super continent

Answer 33

Rhodinia formed during Proterozoic and then split up at the end

Question 34

Phanerozoic:

Answer 34

Paleozoic (248Ma-543Ma) - Mesozoic (65Ma-248Ma) - Cenozoic (0-65Ma)

Question 35

Phanerozoic - Paleozoic era

Answer 35

Starts with first animal shell fossils (545 Ma), rapid increase in animal diversity, land colonized by plants followed by first land animals.

Question 36

Paleozoic ends with ____

Answer 36

permian extinction, a major extinction.

Question 37

Phanerozoic - Mesozoic era

Answer 37

Starts at a major extinction event, age of dinosaurs on land, giants ruled the sea, land and sky

Question 38

Mesozoic:

Answer 38

Triassic Period - Jurassic Period - Cretaceous Period

Question 39

Phanerozoic - Mesozoic - Triassic

Answer 39

Time of transition, Pangaea altered climate and circulation patterns. Diversification of the survivors of the Permian extinction.

Question 40

Phanerozoic - Mesozoic - Jurassic

Answer 40

Big herbivores and nasty carnivores. Pangaea splits.

Question 41

Phanerozoic - Mesozoic - Cretaceous

Answer 41

First fossils of: insects groups, modern mammal and bird groups, flowering plants. Pangaea continues to separate, a few new dinosaurs appeared.

Question 42

Phanerozoic - Cenozoic era

Answer 42

Starts at major extinction event (65 Ma) A 10km in diameter hits Earth.

Question 43

First humans (humanoid)

Answer 43

7 Ma

Question 44

Why did smaller organisms survive the cretaceous period?

Answer 44

Fast reproduction rates, easier to evolve quicker, have higher offspring numbers.