Lecture 8: Geologic Time

Question 1

How many years back to geologic materials record?

Answer 1

4.6 billion

Question 2

What is relative time?

Answer 2

based on the relative timing of geological events (ie the order in which events occurred) events recorded in sequence, no dates involved

Question 3

What is absolute time?

Answer 3

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

Question 4

What is original horizontality?

Answer 4

Sediments and some bodies of extrusive igneous rocks (ex lava flows) are deposited as horizontal layers or strata. This is important bc if strata are not horizontal it means that they were distributed later by tectonic forces.

Question 5

What is original lateral continuity?

Answer 5

The sedimentary strata (layers) are deposited as continuous sheets (within the lateral confines of their area of deposition)
Significance: strata that occur in separate areas, but have idnetitcal rock characteristics can be assumed to have been originally continuous but have been locally eroded

Question 6

What is super position?

Answer 6

States that in any sequence of layered rocks, a given stratum (layer) must be older than any stratum (layer) on top of it

Question 7

What are cross cutting relationships?

Answer 7

Features cut through other features, ex. igneous intrusion BUT a fault in intrusive body must be younger than the rock through which it has cut

Question 8

What is fossil succession?

Answer 8

Fossils occur in a consistent vertical order in sedimentary rocks all over the world, so the relative age represented in rocks can be determined from the fossil content

Question 9

What is missing time and unconformities?

Answer 9

The rate of sediment deposition is not uniform through time. Surfaces representing these slices of missing time are called unconformities.

Question 10

T or F: Uncomformity is a stratum not a surface

Answer 10

False

Question 11

What is disconformity?

Answer 11

Type of unconformity: is a surface overlain and underlain by strata parallel to the surface

Question 12

What is angular unconformity?

Answer 12

Type of unconformity: is a surface that is nounded above by strata parallel to the surface, but bounded below the strata that are titled (not parallel to surface)

Question 13

What is non-conformity?

Answer 13

Type of unconformity: surface bounded above by strata parallel to the surface and below by intrusive igneous rocks or metamorphic rocks

Question 14

How is a disconformity produced?

Answer 14

Sediment layers deposited on seafloor
Sea level drops, exposes seafloor (now land) exposed layers are eroded (producing erosion surface)
Sea level rises, floods land, sediment layers deposited on top of erosion surface (disconformity)

Question 15

How is an angular conformity produced?

Answer 15

Sedimentary strata deformed (folded) during mountain building
Mountains worn down by erosion, producing a flat erosion surface
Sea level rises, erosion surface flooded by sea, sedimentary layers deposited on top of erosion surface (angular unconformity)

Question 16

How are nonconformities produced?

Answer 16

Magma intrudes sedimentary strata producing batholith
Erosion removes sedimentary strata, exposes intrusive igneous rock of batholith, produces flat erosion surface
Sea level rises, erosion surface flooded, sedimentary layers deposited on top of erosion surface.

Question 17

What is an isotope?

Answer 17

Atoms of the same element with differing atomic weights

Question 18

What is a radio isotope?

Answer 18

An isotope that spontaneously changes to another isotops releasing energy in the process

Question 19

How to determine absolute time?

Answer 19

Use the “cocls” ??????provided by atoms and elements contained in minerals

Question 20

What is radioactive decay?

Answer 20

An original radioisotope (parent isotope) is unstable. In most cases a radioisotope will break into a daughter isotope plus subatomic particles, releasing energy in the process (although in some cases, a daughter isotope can be formed in the capture (gain) of electrons)

Question 21

What is radiometric dating? What do the ratios tell us?

Answer 21

The relative ratio of daughter atoms to parent atoms is proportional to the amount of time elapsed since decay began. When all daughter, decay is complete.

Question 22

Define Eon and list it’s names

Answer 22

The greatest expanse of all time

Phanerozoic: visible life—the most recent eon, began abput 542 million years ago
Proterozoic
Archean
Hadean: (the oldest eon)

Question 23

Define Era’s and list its names

Answer 23

Subdivision of Eon

Eras of the Phanerozoic eon
Cenozoic (recent life)
Mesozoic (middle life)
Paleozoic (ancient life)

Question 24

Define Periods and list its names

Answer 24

Subdivision of Era:

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

Question 25

What is the importance of dating rocks?

Answer 25

Theories can be made on what might have happened in the Earth’s past, but it is geology that tells us what will? happen. Rocks are our only basis for interpreting the Earth’s history !