PowerPoint Presentation - Geologic time - USI

Geological Time - really, really, really long! Motion pictures are generally projected at 32 frames per second. Therefore, each frame (image) is on the screen for only split second- let each frame represent 100 years. Start movie at present and go back in time. •The Declaration of Independence would show up 1/16 of a second into the movie. •The Christian era (BC-AD boundary) would be 3/4 of a second into the movie. •The most recent Ice Age would be 7 seconds into it.•The movie would run about 6 hours before we got to the end of the Mesozoic era (extinction of the dinosaurs).•We'd have to watch the movie for about 2 days to see the beginning of the Paleozoic era (macroscopic life). •The whole movie (to the beginning of geologic time on Earth) would be approximately 16 days long!

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

•> Relative: Placing events in a

sequence based on their positionsin the geologic record.> Chronologicsample.

• Two ways to relate time in geology:> Relative: Placing events in a

sequence based on their positionsin the geologic record.> Chronologic: Placing a specific

number of years on an event or rocksample.

Geologic Time

Geologic Time Scale• a combination of the two types of agedeterminations

> a relative sequence of lithologic units - established using logical principles

> measured against a framework ofchronologic dates.

Geologic Time and the "geologic column"• Developed using logical rules to establish relative

sequences of events- - - -

• refined-

•

-

Geologic Time and the "geologic column"• Developed using logical rules to establish

relative sequences of events- superposition- cross-cutting relationships- original horizontality - lateral continuity

• Added to as new information is obtained and data is refined

- Use of fossils for correlation and age determination• Numerical Dates attached to strata after thedevelopment of Radiometric techniques-

Still being refined as more informationbecomes available

The Geologic Time Scale (1:2)

The Geologic Time Scale (2:2)

Relative Dating Methods• determines the relative sequence of events.

> which came first, which came last.> no numeric age assigned

• 6 Relative age principles: > Superposition > Original Horizontality,> Lateral continuity > Cross-cutting Relationships> Inclusions > Fossil succession.

Those in yellow are most useful

History of Historical Geology• Niels Stensen (Nicolaus Steno)

- Fundamental Principles of Relative Time> Principle of Superposition- see below> Principle of Original Horizontality- see below> Principle of Original Lateral Continuity- see below

Law of Superposition• In undisturbed strata, the layer on the bottom is• In undisturbed strata, the layer on the bottom is

oldest, those above are younger.

Original Horizontality•• Sediments are generally deposited ashorizontal layers.

Lateral Continuity•• Sediment layers extend laterally in all

direction until they thin & pinch out asthey meet the edge of the depositionalbasin.

included description and use of

Charles Lyell

• -

> principles of cross-cutting relationships> principles of inclusions

• relative time tools

Charles Lyell

• 1st Principles of Geology text-

> principles of cross-cutting relationships> principles of inclusions

• relative time tools

Cross-cutting Relationships

That which cuts through is younger than the Object that is cut

dike cuts through

granite is cut

Relative Ages of Lava Flows and Sills

Principle of Inclusions• Inclusions (one rock type contained in another rock type) are

older than the rock they are embedded in. That is, the younger rock contains the inclusions

Principle of Inclusions

Faunal/Floral Succession•• Fossil assemblages (groupings of fossils)

succeed one another through time.

- - - -

• Correlation-relating rocks in one location to those in

another using relative age stratigraphicprinciples

- Superposition - Lateral Continuity -

Faunal Succession

- Cross-cutting

••Unconformities

surfacesrepresent a long time.

a time when rocks were notdeposited or a time when rocks wereeroded

Hiatusthe gap in time represented in the rocks by an uncon-formity

3 kinds Angular Unconformity Nonconformity Disconformity

Disconformities A surface of erosion or non-deposition betweenParallel sedimentary rock beds of differing ages.

Angular UnconformitiesAngular Unconformities• An angular unconformity is an erosional surface on tilted

or folded strata, over which younger strata have been deposited.

NonconformitiesA nonconformity is an erosional surface on igneous or

metamorphic rocks which are overlain by sedimentary rocks.

Breakout in to groups and discuss the sequence observed here

Age Estimates of Earth Counting lifetimes in the Bible

Comparing cooling rates of iron pellets.

Determine sedimentation rates & compare

Estimate age based on salinity of the ocean. all age estimates were off by billions of years some were more off than others!

>

+

Absolute Dating MethodsRadioactive Decay sequences acts as an atomic clock

we see the clock at the end of its cycleanalogous to starting a stopwatch

allows assignment of numerical dates torocks.

>

+

decay) into Radioactive isotopes change (daughter isotopes at known rates.

rates vary with the isotopee.g., U , K , C, etc. 235 40 14

•

Decay unstable nuclei in parent isotope emitssubatomic particles and transform intoanother isotopic element (daughter).

does so at a known rate, measured in thelab

Half-life The amount of time needed for one-half of a

radioactive parent to decay into daughterisotope.

Assumptions?-you bet Cross-checks ensure validity of method.

Rate of Decayt0

t1

t 3

All atoms are parent isotope or someknown ratio of parent to daughter

1 half-life period has elapsed, half of thematerial has changed to a daughterisotope (6 parent: 6 daughter)

t22 half-lives elapsed, half of the parentremaining is transformed into a daughterisotope (3 parent: 9 daughter)

3 half-lives elapsed, half of the parentremaining is transformed into a daughterisotope (1.5 parent: 10.5 daughter)

We would see the rock at this point.

Radioactive Isotopes• analogous to sand in an hour glass

- we measure how much sand there is > represents the mass of elements

- we measure the ratio of sand in the bottom to sand in the top - at the end (present)

> daughter (b) and parent (t)- we know at what rate the sand falls into the bottom

> the half life of the radioactive element- how long would it take to get the amount sand in the observed

ratio starting with all of it in the top?

Radioactive Isotopes• analogous to sand in an hour glass

- we measure how much sand there is > represents the mass of elements

- we measure the ratio of sand in the bottom to sand in the top - at the end (present)

> daughter (b) and parent (t)- we know at what rate the sand falls into the bottom

> the half life of the radioactive element- how long would it take to get the amount sand in the observed

ratio starting with all of it in the top?

50

100

2513

time----------->

ParentDaughterParentDaughter

% p

a re n

t rem

a in i

n g

Five Radioactive Isotope PairsFive Radioactive Isotope Pairs

Half-LifeEffective Minerals and

Isotopes of ParentDating Range

Rocks That Can Parent Daughter

(Years)Be Dated

Uranium 238 Lead 206 4.5 billion 10 million to Zircon 4.6 billion UraniniteUranium 235 Lead 207 704 million Thorium 232 Lead 208 14 billion 48.8 billion

Rubidium 87 Strontium 87 4.6 billion 10 million to

Muscovite

Biotite

Potassium feldspar

Whole metamorphic

or igneous rock

Potassium 40 Argon 40 1.3 billion 100,000 to Glauconite 4.6 billion Muscovite Biotite Hornblende Whole volcanic rock

(Years)

4.6 billion

Radiocarbon and Tree-Ring Dating Methods• Carbon-14 dating is based on theratio of C-14 to C-12sample.

> Valid only for samples less than 70,000years old.

> Living things take in both isotopes ofcarbon.

> When the organism dies, the "clock" starts.

• Carbon-14 dating is based on theratio of C-14 to C-12 in an organicsample.

> Valid only for samples less than 70,000years old.

> Living things take in both isotopes ofcarbon.

> When the organism dies, the "clock" starts.

Method can be validated by cross-checking with tree rings

Carbon 14 Cycle

Recognizing Patterns of changeWalther's Law

• The vertical sequence is repeated by the horizontalsequence

- walking from A to B to C to the Coast you would encounter therocks that would be encountered by drilling a core into the

earth at any point (A, B, or C)

Facies Diagram• distribution of lithofacies (rock-types)

- these are associated with their respective EOD• biofacies are similar but refer to fossils rather thanrock types

Eustasy, relative sea-level, and relative positionof lithofacies

• Eustasy= changes in volume of water in ocean• lithofacies depend on

- sea-level- land level- geometry of coast- sediment supply

Vail Curve• an attempt at global• correlation oflithologies

- for better production- of petroleum resources

Rock designations• Rock units called Lithostratigraphic units

- described in terms of Group, Formation, & Member> each term has specific meanings in geological parlance

• Formation - a mappable lithostratigraphic unit

> has a location for identifying the type-section> has a rock designation describing the lithology

- sometimes not all the same lithology> in which case the term "Formation" takes the place of lithologictype

• Groups are composed of several formations• Members are distinctive units within a formation

- group is largest and contains formations and members- formations are next and contain members

Rock designations• Rock units called Lithostratigraphic units

- described in terms of Group, Formation, & Member> each term has specific meanings in geological parlance

• Formation - a mappable lithostratigraphic unit

> has a location for identifying the type-section> has a rock designation describing the lithology

- sometimes not all the same lithology> in which case the term "Formation" takes the place of lithologic

type• Groups are composed of several formations• Members are distinctive units within a formation

- group is largest and contains formations and members- formations are next and contain members

Fundamental lithological unitsFormation- a rock layer with distinctive

characteristics that is mappable over a large are at “typical” map scales

1:62,500 or more commonly 1:24,000Formations have Members

smaller layers that are unique that are not mappable over larger areas and won’t show up at typical map scales Groups have formations; formations have members