The Solid Earth - Chapter 9: Relative Dating

Question 1

Define absolute dating

Answer 1

Defining the exact time in history when something took place

Question 2

Today our understanding of ____ allows us to accurately determine absolute dates for rock units that represent important events in the earth’s distant past

Answer 2

radioactivity

Question 3

This means that rocks are placed in their proper sequence or order and will not tell us how long ago something place, only that it followed one event and preceded another

Answer 3

Relative dating

Question 4

What is the most basic principle of relative dating?

Answer 4

The law of superposition

Question 5

Briefly describe the law of superposition

Answer 5

In an undeformed sequence of sedimentary rocks, each bed is older than the one above it and younger than the one below

Question 6

True or false: the law of superposition does not apply to surface deposited materials like lava flows and ash

Answer 6

False

Question 7

The basic principle that states most layers of sediment are deposited in a nearly horizontal position

Answer 7

Principle of original horizontality

Question 8

Draw a conclusion from the principle of original horizontality

Answer 8

If we observe rock layers that have been folded or inclined at a steep angle, they must have been moved by crustal disturbances sometime after deposition

Question 9

When igneous intrusions or faults cut through other rocks, they are assumed to be ____ than the structure they cut

Answer 9

younger

Question 10

Principle of ___________ maintains that when rocks are cut and offset by a fault, we know they must be older than the fault

Answer 10

cross cutting relationships

Question 11

Pieces of one rock unit that are contained within another

Answer 11

Inclusions

Question 12

The rock mass adjacent to the one containing the intrusions must have been there first in order to provide the ___________

Answer 12

rock fragments

Question 13

Layers of rock are said to be _____ when they are found to have been deposited essentially without interruption

Answer 13

Conformable

Question 14

True or false: there are places on earth that contain a full set of conformable strata

Answer 14

False

Question 15

An _____ represents a period of time during which deposition ceased, erosion removed previously formed rocks, and then deposition resumed

Answer 15

unconformity

Question 16

This type of unconformity is the most easily recognized and consists of tilted or folded sedimentary rocks that are overlain by younger, more flat lying strata

Answer 16

angular unconformities

Question 17

What do angular unconformities imply?

Answer 17

During the pause in deposition, a period of deformation (folding/tilting) as well as erosion occurred

Question 18

What are disconformities?

Answer 18

They are more common than unconformities but less obvious because the strata on either side are essentially parallel

Question 19

What are nonconformities?

Answer 19

These are the type of unconformity that contains a break that separates older metamorphic or intrusive igneous rocks from younger sedimentary strata

Question 20

What are the typical steps of a nonconformity?

Answer 20

There must be a period of uplift and the erosion of overlying rocks. Once exposed at the surface, the igneous/metamorphic subject to weathering and erosion prior to sedimentation

Question 21

Order the rocks in Zion, Bryce Canyon, and Grand Canyon

Answer 21

Oldest: Grand Canyon
Middle: Zion
Youngest: Bryce Canyon