The Sands of Time (L13)

Question 1

What are the 2 concepts of time used in geology?

Answer 1

relative time - based on relative timing of geological events

Absolute time - involves the determination of age in years before present, based on decay of radioactive isotopes

Question 2

How is relative time organized and structured?

Answer 2

earliest event at the bottom of the list and the most recent at the top

Question 3

What is the principal of original horizontality?

Answer 3

an important principle when dealing with layered rocks or “strata”

states that layers of sediment are generally deposited in a horizontal bed

Question 4

What does it mean when strata are flat and horizontal

Answer 4

means it has not been disturbed

Question 5

what does it mean when strata are deformed and/ot not horizontal?

Answer 5

been disturbed by tectonic activity and not in their original state

Question 6

Law of Superposition

Answer 6

states that in an undeformed sequence of sedimentary rocks, YOUNGER strata progressively overlie OLDER strata

basically the youngest rock layer would be at the top of hte stack whereas the oldest rock would be at the bottom

Question 7

What does it reflect that we can use fossils as markers of time intervals?

Answer 7

the useage of fossils as markers of time intervals reflects the fact that evolution is irreversible

Question 8

what does it mean that organisms can’t de-evolve to an earlier form?

Answer 8

means that the range of time a fossil is represented in the rock record is unique to that particular fossil

Question 9

Index Fossils?

Answer 9

fossils that are best suited as indiciators of specific time intervals

Question 10

what are the 4 things that the best index fossils have?

Answer 10

a short time range

well-preserved

easily collected

widely distributed geographically

Question 11

the Law of Cross-cutting Relationships states?

Answer 11

states that a fault or intrusive igneous body must be younger than the rock through which it has cut

fault is younger than the layers

Question 12

What is an inclusion and what do we know about it?

Answer 12

inclusion is a piece of rock that is enclosed within another rock

rock containing the inclusion is YOUNGER than the inclusion itself

Question 13

Law of Inclusions

Answer 13

states that if a rock body (B) contains fragments of another rocky body (A), it must be YOUNGER than the fragments of rock it contains

Rock A must have been there first to provide the fragments

Question 14

What do inclusions in igneous rock bodies tend to be?

Answer 14

tend to be rock fragments dislodged from walls of magma chamber

Question 15

What do inclusions in sedimentary rocks tend to be?

Answer 15

rock fragments eroded from underlying rocks

Question 16

the rate of sediment deposition is _____ through time

Answer 16

not uniform

Question 17

How does a deposition become not uniform?

Answer 17

when there are significant pauses in sediment deposition, or in extreme cases, rocks can be removed by erosion

“time” in the form of rock goes missing

Question 18

What happens when deposition resumes after the interruption?

Answer 18

a distinct (and often irregular) surface is produced

Question 19

Uncomformity

Answer 19

a break in the rock record produced by erosion and/or nondeposition of rock units.

its a surface, not a unit of rock

Question 20

3 types of unconformities

Answer 20

Angular unconformity – surface underlain by tilted strata and overlain by flat-lying strata

A disconformity – surface underlain by flat-lying strata and overlain by flat-lying strata

Noncomformity – surface underlain by metamorphic or plutonic igneous rocks and overlain by flat-lying strata

Question 21

What happens when land is uplifted above sea level or if the sea level falls? Why?

Answer 21

the exposed land will eventually erode to a flat surface

Because land above sea level tends to wear down while ocean basins tend to be filled up with sediment

Question 22

Where is a good place where you can see all three types of unconformity?

Answer 22

Grand Canyon

Question 23

What does the principle of relative time allow us to do?

Answer 23

deduce the order in which such events have occured

Question 24

atoms of the same element with differing atomic weights are called

Answer 24

isotopes

Question 25

What is the process called where certain isotopes (parent isotopes) will lose particles to form isotopes of new elements (daughter isotopes)

Answer 25

radioactive decay

Question 26

Rates of decay are commonly expressed in terms of

Answer 26

Half-life

Question 27

Half-life?

Answer 27

the time required for half of the atoms in a sample to decay to daughter products

Question 28

How do half-life’s work?

Answer 28

it represents the “halving” of the preceding amount of parent isotope

Question 29

How would you date minerals in a clastic sedimentary rock?

Answer 29

you would obtain the age the particles came from and NOT the sedimentary rock body itself

Question 30

The “Master Timetable”for the Earth

Answer 30

Geologic Time Scale - born from concepts of relative time with emphasis on time slices represented by distinctive fossil forms

Question 31

3 reasons why geologic time scale is important?

Answer 31

serves as a framework for the timing of geological events

makes scientific communication more efficient

comprises a hierarchy of time units similar to a regular calendar

Question 32

What are the 3 main time scales focused on in this course?

Answer 32

Eon - Largest
Era
Periods

Question 33

What are Earth’s history divided into? (Oldest to Youngest)

Answer 33

Hadeon Eon - hellish world
Archean Eon - rocks
Proterozoic Eon - “earlier life”
Phanerozoic Eon - “visible life”

Question 34

What are the 3 eras? (Pahenrozoic Eon focused) Oldest to Youngest

Answer 34

Paleozoic (ancient life)
Mesozoic (middle life)
Cenozoic (recent life)

Question 35

What are the order of Periods? Oldest to Youngest

Answer 35

Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian, Triassic, Jurassic, Cretaceous, Paleogene, Neogene, Quaternary

Question 36

Where are the names of Periods derived from?

Answer 36

“Type” localities
Rock characteristics
Various whim