Week 5

Question 1

Relative Time

Answer 1

based on the relative timing of geological events (i.e. the order in which events occurred)

Question 2

Absolute Time

Answer 2

the determination of age in years before present, based on the decay of radioactive isotopes.

Question 3

Law of Original Horizontally

Answer 3

Sediments and some bodies of extrusive igneous rocks are deposited as horizontal layers (strata).
States that strata are laid down horizontally.
If strata are not horizontal, it means that they were disturbed later by tectonic forces.

Question 4

Law of Superposition

Answer 4

In any sequence of layered rocks, a given stratum must be older than any stratum on top of it.

Question 5

Law of Fossil Succession

Answer 5

Fossils occur in a consistent vertical order in sedimentary rocks all over the world.
Thus the relative age of “slices” of time represented in rocks can be determined from the fossil content of rocks.

Question 6

Law of Cross-cutting relationships

Answer 6

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

Question 7

Inclusions

Answer 7

Dislodged fragments of rock that are incorporated into younger rocks

Question 8

Law of Inclusions

Answer 8

if a rock body (Rock B) contains fragments of another rock body (Rock A), it must be younger than the fragments of rock it contains; Rock A must have been there first to provide the fragments.

Question 9

Inclusions in igneous rock bodies

Answer 9

dislodged from walls of magma chamber

Question 10

Inclusions in sedimentary rocks

Answer 10

fragments eroded from underlying rocks

Question 11

Unconformities

Answer 11

The rate of sediment deposition is not uniform through time

Question 12

Nonconformities

Answer 12

An unconformity that separates underlying metamorphic or igneous rocks from overlying horizontal sedimentary strata.

Question 13

Angular Unconformity

Answer 13

Separates underlying tilted rocks from overlying horizontal sedimentary rocks.

Question 14

Disconformity

Answer 14

Separates underlying horizontal sedimentary rocks from from overlying horizontal sedimentary rocks.

Question 15

Isotopes

Answer 15

Atoms of the same element with differing atomic weights

Question 16

Radioactive Decay

Answer 16

Certain isotopes (parent isotopes) will lose/gain particles in its nucleus to form isotopes of a new elements (daughter isotopes), releasing energy in the process

Question 17

Radiometric Dating

Answer 17

The higher the proportion of daughter atoms to parent atoms, the older the sample

Question 18

Half Life

Answer 18

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

Question 19

Importance of the Geological Time Scale

Answer 19

1) Provides a framework for the timing of geological events
2) Makes scientific communication more efficient
3) Comprises a hierarchy of time units so that time can be expressed in both large and small units

Question 20

The Rock Cycle

Answer 20

The cycle of rock recycling

Question 21

Athenosphere

Answer 21

not quite a liquid, but flows like a liquid over long periods of time

Question 22

Mohorovicic discontinuity

Answer 22

The boundary between the crust and mantle
Called “Moho” for short

Question 23

Convection Model

Answer 23

convection currents in the asthenosphere drag the lithospheric plates along

Question 24

Ridge-Push Model

Answer 24

plates are actively pushed from sites of spreading as magma is injected and plates slide down flanks of mid-ocean ridges under the influence with gravity

Question 25

Slab-Pull Model (most likely)

Answer 25

Slab could be pulled by the sinking, leading edge of the plate

Question 26

Divergent Boundaries

Answer 26

represented by mid-ocean ridges

Question 27

Convergent Boundaries

Answer 27

represented by trenches

Question 28

Erosion

Answer 28

the physical removal of material by mobile agents such as water, wind, ice, or gravity.

Question 29

Frost-Wedging

Answer 29

Occurs when liquid water penetrates cracks within a rock and freezes Water expands when it converted to ice, widening the cracks

Question 30

Freeze-thaw weathering

Answer 30

With repeated cycles of water penetration and freezing, cracks get increasingly large, ultimately resulting in the breakup of the material

Question 31

Root wedging

Answer 31

Occurs when roots of plants (e.g. trees) penetrate into small cracks. As the root increases in size, it increases the size of the crack until pieces of the rock break apart.

Question 32

Unloading

Answer 32

When a plutonic igneous rock body expands as overlying rock is removed by erosion. Outer layers of the intrusion expand more than the rock below and separate like layers of an onion (exfoliation). Sheets of igneous rock “pop” off the surface as the body continues to expand.

Question 33

Dissolution

Answer 33

The process in which a material is dissolved in a liquid

Question 34

Oxidation

Answer 34

Occurs when oxygen combines with another element to form an oxide that can be subsequently removed by erosion. EX. Rust (iron forming hematite)

Question 35

Hydrolysis

Answer 35

when minerals react with water to form other products.

Question 36

Why is liquid water one of Earth's most potent agents of erosion?

Answer 36

1) It can transport dissolved substances released by chemical weathering. 2) Flowing water can loosen and pluck particles. 3) These particles, in turn, can impact underlying rock and abrade it.

Question 37

Erosion by wind (deflation)

Answer 37

Flowing air, much like flowing water, also plucks grains that are loosened by weathering, and can produce similar effects of erosion.

Question 38

Erosion by ice

Answer 38

Like water and wind flowing glacial ice can pluck loose sediment grains from the ground. Plucked fragments of rock under the ice can then abrade rock as they are dragged across the bed of the glacier.

Question 39

Erosion by Gravity

Answer 39

Material weakened by weathering can fail and be transported downslope. The rapid downslope movement of materials due to gravity is called mass-wasting