Objectives:

Define Relative Age

Define Absolute Age

Explain the principles of relative time including uniformitarianism, superposition, and original horizontality

Explain how geologic events can be used to determine relative time including inclusions, cross-cutting relationship, contact metamorphism, and unconformities

Describe radioactive decay

Calculate half-life of a radioactive isotope

Identify various types of fossils

Explain the various theories of how life began on Earth

Explain extinction

Define Index fossils

Explain the differences in each of the major geologic eras

Know how to use Geologic History of New York State chart ESRT page 8 and 9

I. Fossils and the Past

A. A fossil is the remains or the evidence of a living thing.

B. Formation of Fossils:1. Most fossils are incomplete because usually only the hard parts of a plant or animal become fossils.

2. The soft flesh of dead organisms was usually eaten by animals or decayed before it could form into a fossil.

3. Circle the organisms below that would most likely become a fossil.

2. a. Most fossils form when organisms are buried in sediments.

b. Sediments often harden and change into rock. When this happens, organisms may be trapped in the rock.

Most fossils are found in ________________ rocks. Sedimentary

Living Organism

Burial of hard parts by sediments

Sediment becomes rock

Uplifting-

Weathering & erosion

expose fossil

c. Fossils are almost never found in ___________ rocks because magma is found deep within Earth where no living things exist, and lava at the surface burns organisms before fossils can form.

d. Fossils are rarely found in _______________ rocks because heat, pressure, and/or chemical activity that causes a rock to change, also destroys or damages the fossils.

Igneous

Metamorphic

C. Types of Fossils

1. ___________________ and __________________

a. ________________ an empty space in the shape of the organism. This occurs when the hard parts of an organism decay and/or the hard parts are dissolved by chemicals.

b. _______________ occurs when minerals fill a mold and harden into the shape of the original organism.

Casts Molds

Cast

Mold

2. ___________________- occurs when leaves and feathers leave an impression in soft sediment (mud) that later hardens into rock.

3. __________________ - occurs when insects are trapped and become embedded in resin (tree sap) that hardens.

Imprints (Impressions)

Amber

4. __________________ - occurs when an organism is preserved in ice.

5. __________________ - occurs when animals are trapped in tar pits as in the LaBrea Tar Pits of California.

Ice

Tar

http://www.mc.maricopa.edu/dept/d10/asb/anthro2003/legacy/iceman/iceman.html

"In order for a body to be completely mummified as in this case, the body must first dry completely then covered in ice and snow." The mummy was an male adult remarkably well preserved. The condition of his equipment and organic material were also preserved in good condition. The age of the body is about 3,300 BC or late Stone Age.

7. __________________ - occurs the carbon in the tissues of organisms leave a residue/thin film of carbon on sediment which then hardens into rock.

6. __________________ - occurs minerals dissolved in ground water gradually replace the original tissues of plants and animals.

Petrified

Carbonaceous film

D. Interpreting Fossils

1. Fossils indicate that many different kinds of life forms existed at different times in Earth’s history.

2. When fossils are arranged according to age, they show that

Certain living things have changed or evolved over time.

3. Fossils indicate how

For example, fossils of marine organisms can be found in rocks that are presently high above sea level.

the Earth’s surface has changed.

4. Fossils give clues to

Since coral today live in the warm waters of equatorial regions, between 30° N and 30° S latitude, we can infer that

Earth’s past climate.

N.Y.S. had a warmer climate in the past.

5. Fossils tell about the

appearance and activities of past life.

For example, fossil teeth give clues about the kind of food the animal ate.

II. Relative Dating

A. Relative Age- the age of something compared to something else.

B. The Geologic Column- an ideal sequence of rock layers created by combining data from all known rock sequences at various locations.

Correlation

C. Principle of Superposition-

In an undisturbed set of sedimentary rock layers, the oldest rock is at the bottom and the youngest is on the top.

YOUNGEST

OLDEST

D. Disturbed Rock Layers and Relative Dating

A fault is ______________ than the rock layers it cuts across.

An igneous intrusion is ______________ than the rock layers it penetrates

YOUNGER

YOUNGER

“Principle of Cross-Cutting Relationships”

= Contact metamorphism

The folding and tilting of rock layers are events that are ___________ than the rock layers they effect.

YOUNGER

“ Principle of Original Horizontality”

Layers of sediment are deposited in flat-lying layers

The photograph represents a mountainous area in the Pacific Northwest.  Scientists believe that sedimentary rocks like these represent evidence of crustal change because these rocks were1. formed by igneous intrusion 2. faulted during deposition 3. originally deposited in horizontal layers 4. changed from metamorphic rocks

E. Unconformity- A buried erosional surface separating two rock layers of different ages that show that sediment deposition was not continuous.

Deposition- formation of horizontal rock layers

Uplifting/ folding

Erosion of surface layers

Subsidence- sinking down of earth’s layers followed by deposition of new sedimentary layers

Unconformity

The unconformities shown in the cross section represent

1. buried erosional surfaces 2. locations of index fossils 3. volcanic ash deposits 4. boundaries between oceanic and continental crust

The unconformities shown in the cross section represent

1. Letter X2. Letter E3. Letter Q4. Letter Y

F. Index Fossils- a fossil that is used to date the rock layers in which it is found.

1. An organism that lived during a relatively short, well-defined time span.

2. Organism lived in a wide geographic area.

G. Determining Relative Age:

Identify both the oldest rock or event and the youngest rock or event:

SiltstoneShale

12

3

4

ConglomerateFault1

2

34

56

Shale

Sandstone

ShaleSiltstone

SandstoneShale

3.

4.

5.

Limestone

Sandstone

Igneous Intrusion

Igneous Intrusion

6.

7.

Shale

Fault

Siltstone

Igneous Intrusion

III. Radioactive Dating- determining the absolute age of a rock or fossil

A. Absolute Age- the measure of how many years old an event occurred or an organism lived.

B. Radioactivity- the ability of an element to change spontaneously into a different element by losing or gaining matter from the nucleus of an atom.

E.S.R.T

page ____

1

C. Radioactive Decay

1. __________ or _______ element = an atom that has an unstable nucleus that changes spontaneously, or “decays”.

Radioactive parent

2. __________ or __________element = the stable element that is the result of the spontaneous change in a radioactive element.

Decay daughter

3. Half-life = the TIME it takes for ONE-HALF of a radioactive element to change into a decay element.

Or PARENT Daughter element

4. The rate of decay (the half-life period of time) is NOT affected by any outside condition such as:

a.

b.

c.

Heat

Chemical action

Pressure

Half-lives of radioactive elements are unique for each element

Radioactive Element

Half-life (years)

Decay Element

Potassium-40 1.3 x 109 Argon-40

Calcium-40

Rubidium-87 4.9 x 10 10 Strontium

Uranium-238 4.5 x 10 9 Lead-206

5. ______________ has a short half-life and is therefore used to date the remains of __________________ such as

_______________________________________________________.

Carbon-14Living things

Bones, Wood, Leather

Carbon-14 5.7 x 103 Nitrogen-14

1:1 1:3 1:7 1:16

100%

50%

25%

12.5%

6.25%

Radioactive Decay PowerPoint

Practice: Making a Time-Table (T-table)

After an organism dies, how much percent of Carbon-14 is remaining after 5 half-lives?

MassTime

0 100%

1 50%

2 25%

3 12.5%

4 6.25%

5 3.125%

Practice: Making a Time-Table (T-table)

If a dinosaur contained 200 grams of Carbon-14, how much will be remaining after 34,200 years?

Mass (grams)Time (yrs)

0 200

5700 100

11,400 50

17,100 25

22,800 12.5

28,500 6.25

34,200 3.125

Mass (grams)Time (yrs)

0 8

A rock sample contains 8 grams of Potassium-40 when it was formed but now contains only 2 grams due to radioactive decay. What is the approximate age of this rock?

IV. Geologic Time

A. The Geologic Time Scale divides Earth’s history into sections of time.

B. The units or sections of geologic time include:

1.

2.

3.

4.

Eon

Era

Period

Epoch shortest

longest

C. The boundaries between geologic time intervals represent major changes on Earth which include:

1. 2.3.

D. Geologic Time began when Earth first formed about______________________ years ago.4600 million

Emergence of different life

Peak Developments of species

Major Extinctions

Formation of EarthToday

Precambrian

4,500

544

39563956= 88%

450022 cm

Precambrian

Paleozoic

251293

293= 6.5%

45001.625 cm

Paleozoic

Mesozoic

65186

186= 4%

45001 cm

Mesozoic

Cenozoic0

6565 = 1.4%

45000.35 cm

Cenozoic

Life

Soft-bodied

Marine animals with shellsTrilobites

fish

Invertebrates

Land plants

insects Eurypterids

Armored fish

amphibians

forests

reptiles

Corals

reptiles

~90% of lifemammals

dinosaurs

dinosaurs birds

Flowering plantsdinosaurs

~50% of life

mammals

humans

?

?

?

11,400