Reading the Rocks

Question 1

Catastrophism

Answer 1

The dominant view in the late 1700s that maintains that the earth is ancient and its strata were formed by catastrophes. In this view, after each catastrophe, God would replenish the world with new organisms. Noah’s Flood was only the most recent catastrophe.

Question 2

Uniformitarianism

Answer 2

(originated with James Hutton in 1788 and popularized by Charles Lyell in Principles of Geology)
“the present is the key to the past”
rejects catastrophes as the origins for geologic strata; instead it holds that the geology of the past happened slowly and only today’s rates and processes could be applied to the geologic record.

Question 3

Actualism

Answer 3

a modified uniformitarianism that is more willing to consider catastrophes. It holds that the geological processes that worked in the past were similar to those in operation today [i.e. slowly], though the scope and magnitude may be different.

Question 4

Relative dating

Answer 4

Methods used to determine the sequences and order in which geological events occurred without giving an exact age

Question 5

To which rocks can the rules of stratigraphy be applied?

Answer 5

Layers of sedimentary rocks and extrusive igneous rocks

Question 6

rules of stratigraphy

Answer 6

the law of original horizontality
the law of superposition
the law of lateral continuity

Question 7

law of original horizontality

Answer 7

when sediments/lava are deposited, they’re spread out in flat sheets; therefore, tilting, faulting, and folding happen after strata have been laid down flat

Question 8

law of superposition

Answer 8

older units are found below younger units
(applies ONLY to undisturbed sedimentary and extrusive igneous rocks)

Question 9

law of lateral continuity

Answer 9

sedimentary/extrusive igneous rocks remain in the same composition in all directions when deposited until they either contact an edge or wall to a depositional environment or thin out as energy levels decrease

Question 10

Walther’s Law

Answer 10

In a vertical sequence of sedimentary rocks, the types of rock found above and below each other are the same as those found in adjacent sedimentary environments

Question 11

rule of inclusions

Answer 11

when a rock includes pieces of another rock inside of it, the included pieces must be older than the rock containing them

Question 12

principle of cross-cutting relationships

Answer 12

geological structures or features (such as dikes, faults, or erosion surfaces) must be younger than the geological units they affect

Question 13

unconformities

Answer 13

surfaces within rocks that represent a break in time (could happen because of erosion or a lack of sedimentation [a hiatus])

Question 14

3 types of unconformities

Answer 14

disconformity
angular unconformity
nonconformity

Question 15

disconformity

Answer 15

an unconformity located between 2 roughly parallel sedimentary or extrusive igneous units
(these can be difficult to identify if there isn’t an erosion surface)

Question 16

angular unconformity

Answer 16

an unconformity where the sedimentary rocks or extrusive igneous rocks above and below the unconformity are oriented at different angles
they form when rocks, originally laid down flat, are tilted and then eroded; a new flat layer is then deposited on top.

Question 17

nonconformity

Answer 17

an unconformity located at the contact of a sedimentary or extrusive igneous rock and an intrusive igneous or metamorphic rock
Can be either erosion down to a crystalline (igneous or metamorphic) rock with deposition of a sedimentary rock on top or intrusion of an igneous rock into sedimentary rocks.