geologic time 1. which geologic event took place first and when? when? which rock layer is older,...

Geologic TimeGeologic Time

1

• Which geologic event took place first andWhich geologic event took place first and when?when?

• Which rock layer is older, and how is earthWhich rock layer is older, and how is earth history deciphered?history deciphered?

• How do we assign actual years to rock layers?How do we assign actual years to rock layers?

• Which geologic event took place first andWhich geologic event took place first and when?when?

• Which rock layer is older, and how is earthWhich rock layer is older, and how is earth history deciphered?history deciphered?

• How do we assign actual years to rock layers?How do we assign actual years to rock layers?

Consider:Consider:1111

2222

3333

4444

5555Sandstone (ss)Sandstone (ss)

Limestone (LS)Limestone (LS)

Shale (sh)Shale (sh)

ssss

The earth needs atime scale

The earth needs atime scale

Historical aspects about geologyHistorical aspects about geology

There are two schools of thought on the There are two schools of thought on the geologic history and processes that formed geologic history and processes that formed our earth.our earth.

Historical aspects about geologyHistorical aspects about geology

There are two schools of thought on the There are two schools of thought on the geologic history and processes that formed geologic history and processes that formed our earth.our earth.

Catastrophism vs. UniformitarianismCatastrophism vs. UniformitarianismCatastrophism vs. UniformitarianismCatastrophism vs. Uniformitarianism

4

CatastrophismCatastrophism: (mid-1600’s): (mid-1600’s)

powerful geologic events that powerful geologic events that shape the earth in a single shape the earth in a single incidentincident

Volcanic eruptionsVolcanic eruptions

EarthquakesEarthquakes

Massive floodsMassive floods

LandslidingLandsliding

CatastrophismCatastrophism: (mid-1600’s): (mid-1600’s)

powerful geologic events that powerful geologic events that shape the earth in a single shape the earth in a single incidentincident

Volcanic eruptionsVolcanic eruptions

EarthquakesEarthquakes

Massive floodsMassive floods

LandslidingLandsliding

5

CatastrophismCatastrophism: (mid-1600’s): (mid-1600’s) published by Anglican Archbishop, Jamespublished by Anglican Archbishop, James

UssherUssher

determined that earth was only a few determined that earth was only a few

thousand years old – created in 4004 BCthousand years old – created in 4004 BC

suggested that earth landscapes are suggested that earth landscapes are

fashioned by great catastrophes fashioned by great catastrophes

an attempt to fit the formation of earth an attempt to fit the formation of earth

features into a short amount of time features into a short amount of time

(6000 years – Biblical philosophy)(6000 years – Biblical philosophy)

CatastrophismCatastrophism: (mid-1600’s): (mid-1600’s) published by Anglican Archbishop, Jamespublished by Anglican Archbishop, James

UssherUssher

determined that earth was only a few determined that earth was only a few

thousand years old – created in 4004 BCthousand years old – created in 4004 BC

suggested that earth landscapes are suggested that earth landscapes are

fashioned by great catastrophes fashioned by great catastrophes

an attempt to fit the formation of earth an attempt to fit the formation of earth

features into a short amount of time features into a short amount of time

(6000 years – Biblical philosophy)(6000 years – Biblical philosophy)

6

UniformitarianismUniformitarianism – Birth of Modern Geology – Birth of Modern Geology

• “ “The present is the key to the past.”The present is the key to the past.”

UniformitarianismUniformitarianism – Birth of Modern Geology – Birth of Modern Geology

• “ “The present is the key to the past.”The present is the key to the past.”

Uniformitarianism states:Uniformitarianism states:

Physical, chemical, and biological laws that Physical, chemical, and biological laws that operate today have also operated in the operate today have also operated in the

geologic past.geologic past.

Uniformitarianism states:Uniformitarianism states:

Physical, chemical, and biological laws that Physical, chemical, and biological laws that operate today have also operated in the operate today have also operated in the

geologic past.geologic past.

Proposed by James Hutton – late 1700’s• argued using the “rock cycle” concept• argued using earth processes that can be observed• What is required? TIME

Proposed by James Hutton – late 1700’s• argued using the “rock cycle” concept• argued using earth processes that can be observed• What is required? TIME

7

The Uniformitarianism philosophyThe Uniformitarianism philosophyDo geologic processes act Do geologic processes act slowlyslowly or or rapidly?rapidly?

How many catastrophic events take place/day?How many catastrophic events take place/day?

When was the last major volcanic When was the last major volcanic eruption?eruption?

When was the last major earthquake?When was the last major earthquake?

How long does it take a river to carve a How long does it take a river to carve a canyon?canyon?

How fast are the continents moving?How fast are the continents moving?

Do you consider yourself a Do you consider yourself a catastrophistcatastrophist or a or a uniformitarianist?uniformitarianist?

The Uniformitarianism philosophyThe Uniformitarianism philosophyDo geologic processes act Do geologic processes act slowlyslowly or or rapidly?rapidly?

How many catastrophic events take place/day?How many catastrophic events take place/day?

When was the last major volcanic When was the last major volcanic eruption?eruption?

When was the last major earthquake?When was the last major earthquake?

How long does it take a river to carve a How long does it take a river to carve a canyon?canyon?

How fast are the continents moving?How fast are the continents moving?

Do you consider yourself a Do you consider yourself a catastrophistcatastrophist or a or a uniformitarianist?uniformitarianist? 8

Taking Uniformitarianism literally – Problem with Taking Uniformitarianism literally – Problem with “U”“U”

RatesRates and and intensitiesintensities of geologic processes of geologic processes change over time. change over time.

Example:Example:

10,000 years ago, large land masses were 10,000 years ago, large land masses were covered in ice.covered in ice.

Different type of geologic environment Different type of geologic environment than todaythan today

Different intensityDifferent intensity

Different rates of erosionDifferent rates of erosion

Given the concept of Uniformitarianism, would Given the concept of Uniformitarianism, would you consider the earth to be very you consider the earth to be very OLDOLD or very or very YOUNG?YOUNG?

Taking Uniformitarianism literally – Problem with Taking Uniformitarianism literally – Problem with “U”“U”

RatesRates and and intensitiesintensities of geologic processes of geologic processes change over time. change over time.

Example:Example:

10,000 years ago, large land masses were 10,000 years ago, large land masses were covered in ice.covered in ice.

Different type of geologic environment Different type of geologic environment than todaythan today

Different intensityDifferent intensity

Different rates of erosionDifferent rates of erosion

Given the concept of Uniformitarianism, would Given the concept of Uniformitarianism, would you consider the earth to be very you consider the earth to be very OLDOLD or very or very YOUNG?YOUNG? 9

I I I I my earth science class. my earth science class. my earth science class. my earth science class.

I will get an A on my exams and quizzes.I will get an A on my exams and quizzes.

Discuss with a friend:Discuss with a friend:

1.1.Describe the differences betweenDescribe the differences between catastrophismcatastrophism and and uniformitarianism.uniformitarianism.

2. Provide at least 2 examples each of 2. Provide at least 2 examples each of catastrophism and uniformitarianism.catastrophism and uniformitarianism.

3. Identify “problems” with both philosophies.3. Identify “problems” with both philosophies.

10

Relative Dating - placing the geologic occurrence in the proper sequence

Relative Dating - placing the geologic occurrence in the proper sequence

Which came first and WHY?Which came first and WHY?

To construct a “relative” time scale, rules were To construct a “relative” time scale, rules were established (principles of relative dating).established (principles of relative dating). Nicholas Steno Nicholas Steno (1636-1686)(1636-1686)

• Principle of Original HorizontalityPrinciple of Original Horizontality• Law of SuperpositionLaw of Superposition• Principle of Cross-Cutting RelationsPrinciple of Cross-Cutting Relations• Principle of InclusionsPrinciple of Inclusions

Which came first and WHY?Which came first and WHY?

To construct a “relative” time scale, rules were To construct a “relative” time scale, rules were established (principles of relative dating).established (principles of relative dating). Nicholas Steno Nicholas Steno (1636-1686)(1636-1686)

• Principle of Original HorizontalityPrinciple of Original Horizontality• Law of SuperpositionLaw of Superposition• Principle of Cross-Cutting RelationsPrinciple of Cross-Cutting Relations• Principle of InclusionsPrinciple of Inclusions

11

Let’s unravel some geologic history from observations of various formationsLet’s unravel some geologic history from observations of various formationsand their contacts.and their contacts.

Nicholas Steno – 1669 proposed the following relative dating principles:Nicholas Steno – 1669 proposed the following relative dating principles:

The Principle of Original Horizontality:•Sedimentary rock layers are deposited as horizontal strata.

•Any observed non-horizontal strata have been disturbed.

basin

Sediment inputSediment input

AA

BB

CC

12

Limestone (ls)

Shale (sh)

Sandstone (ss)

granitic rock

Original Horizontal Strata

13

The Principle of The Principle of SuperpositionSuperposition

In any undisturbed sequence of strata, In any undisturbed sequence of strata, the oldest stratum is at the bottom the oldest stratum is at the bottom of the sequence, and the youngest of the sequence, and the youngest stratumstratum

is on top.is on top.

The Principle of The Principle of SuperpositionSuperposition

In any undisturbed sequence of strata, In any undisturbed sequence of strata, the oldest stratum is at the bottom the oldest stratum is at the bottom of the sequence, and the youngest of the sequence, and the youngest stratumstratum

is on top.is on top.

1

2

3

4

5

Unit 1 = oldUnit 5 = youngUnit 1 = oldUnit 5 = young

14

Which strata is older?

1

2

3

4

554321 oldest

youngest

15

The principle of The principle of Cross-Cutting RelationshipsCross-Cutting Relationships

•Any geologic feature that cuts across another Any geologic feature that cuts across another geologic feature is geologic feature is younger.younger.

The principle of The principle of Cross-Cutting RelationshipsCross-Cutting Relationships

•Any geologic feature that cuts across another Any geologic feature that cuts across another geologic feature is geologic feature is younger.younger.

1

2

3

4

5

6

Unit 1 = olderUnit 6 = youngestUnit 1 = olderUnit 6 = youngest

Which came first:Unit 5 or Unit 6?Which came first:Unit 5 or Unit 6?

16

Which is older, the faultor volcanic layer?

Which is older, the faultor volcanic layer?

Volcanic layerVolcanic layer

faultfault

What type of fault is this?

What type of fault is this?

Which is younger, the dikeor country rock?

Which is younger, the dikeor country rock?

country rockcountry rock

dikedike

Determine the relative age of the two dikes.Determine the relative age of the two dikes.

1122

NormalNormal

17

The Principle of The Principle of InclusionsInclusions

•A piece of rock (clast) that has become “included” A piece of rock (clast) that has become “included” in another rock body is in another rock body is olderolder than the rock body than the rock body it has become part of – why?it has become part of – why?

Rock body Rock body AA

Intrusion of pluton BIntrusion of pluton B

AA A

Older (Rock A was there first.)

18

Which “granites” are older and younger?Which “granites” are older and younger?

OLDEROLDERYOUNGERYOUNGER

19

Which rock body is older?:Which rock body is older?:

AA

BB

CC??

??

Can you identify the inclusionsfound in this Sierra NevadaMountain batholitic material?

Can you identify the inclusionsfound in this Sierra NevadaMountain batholitic material?

20

YoungestYoungest

OldestOldest

SuperpositionSuperposition

Original HorizontalityOriginal Horizontality

Cross-Cutting RelationshipCross-Cutting Relationship

A B C Asp Vn

Principle of Inclusions

Principle of Inclusions

Which granite is older?Which granite is older?

OlderOlder YoungerYounger21

I I I I this earth science class. this earth science class. this earth science class. this earth science class.

I will get an A on my exams and quizzes.I will get an A on my exams and quizzes.I will get an A on my exams and quizzes.I will get an A on my exams and quizzes.

Discuss with a friend:Discuss with a friend:Discuss with a friend:Discuss with a friend:

4. Explain the concept of 4. Explain the concept of relative dating.relative dating.5. Draw a diagram, and explain each of the5. Draw a diagram, and explain each of the following dating principles:following dating principles:

Original HorizontalityOriginal HorizontalitySuperpositionSuperpositionCross-Cutting RelationsCross-Cutting Relations Inclusion PrincipleInclusion Principle

4. Explain the concept of 4. Explain the concept of relative dating.relative dating.5. Draw a diagram, and explain each of the5. Draw a diagram, and explain each of the following dating principles:following dating principles:

Original HorizontalityOriginal HorizontalitySuperpositionSuperpositionCross-Cutting RelationsCross-Cutting Relations Inclusion PrincipleInclusion Principle

22

Ok – given the principles, what is wrong with this stack of rock (strata)

123567

Missing time – or does time really stop?

oldest

youngest

23

The principle of The principle of UnconformitiesUnconformities

•rock surface that represents a period of erosion or rock surface that represents a period of erosion or non- depositionnon- deposition•referred to as “missing time”referred to as “missing time”•three major types of unconformities:three major types of unconformities:

•disconformitydisconformity•angular unconformityangular unconformity•non-conformitynon-conformity

Unconformity

disconformitydisconformity – unconformity in non-disturbed unconformity in non-disturbed sedimentary layerssedimentary layers

angular unconformityangular unconformity – uncon. lies between angled – uncon. lies between angled strata and overlying strata and overlying horizontal stratahorizontal strata

non-conformity non-conformity – sedimentary strata– sedimentary strata overlies crystallineoverlies crystalline rocks (ig and met)rocks (ig and met)

Igneous or metamorphic rockIgneous or metamorphic rock 24

Xln rocksXln rocks

Sedimentary rocksSedimentary rocks

disconformitydisconformity

angularunconformity

angularunconformity

nonconformitynonconformity

25


I will get an A on my exams and quizzesI will get an A on my exams and quizzesDiscuss with a friendDiscuss with a friend

6. Explain what an unconformity is and6. Explain what an unconformity is and what it represents.what it represents.

7. Diagram pictures that represent the 7. Diagram pictures that represent the three types of three types of unconformities.unconformities.

26

Fossils – evidence of past life or “time pieces,” the remains or traces of prehistoric life

Paleontology – study of fossils

How do we get a fossil? – preservation of past lifeHow do we get a fossil? – preservation of past life

• 2 conditions must exist for preservation2 conditions must exist for preservation• rapid burialrapid burial• possession of hard partspossession of hard parts

Prehistoric bug

Bug dies Bug soft parts areeaten or dissolve

Rapid burial ofsediment coversthe bug – fossil

27

Fossils – evidence of past life or “time pieces,”

the remains or traces of prehistoric lifePreservation of fossils

• Small percentage of fossils preserved throughout geologic time – WHY?

Most organisms composed of soft parts.

Organisms with hard parts and within a sedimentary environment are favored.

Very rare to see vast array of other life forms

How do fossils help scientists relatively date layersof rock (strata)? 28

William Smith – Principle of Fossil Succession

Fossil organisms succeed one another in a definite and determinable order, and thereforeany time period can be recognized by its fossilcontent.

“Fossils are arranged according to their age by using the law of superposition.”

Fossil succession:• allows geologists to age date wide geographicalallows geologists to age date wide geographical areasareas• documents the evolution of life

• Age of mammals• Age of reptiles• Age of fish Oldest

Youngest

29

How do fossils help date rocks?1200 miles

Which fossils are the youngestand oldest?

DisconformityDisconformity

11

22

33

55

66

77

22

33

44

6677

30


I will get an A on my exams and quizzes.I will get an A on my exams and quizzes.Discuss with a friend:Discuss with a friend:

8. Give 2 reasons why many organisms are8. Give 2 reasons why many organisms are are not fossilized.are not fossilized.

9. Explain the law of fossil succession and9. Explain the law of fossil succession and how this law allows dating of strata.how this law allows dating of strata.

10. How has fossil succession helped 10. How has fossil succession helped geologists unravel earth history?geologists unravel earth history?

OK – We have relative dating and fossils – How dowe get “absolute” ages on the rocks (numbers)?

Radiometric dating – applying a number• radioactive atoms (isotopes) decay at a constant rate over time

33

Radioactive decay of anunstable isotope atom

++

++++

++++

++ ++

++

++

++++

Decay process

• The time of decay can be measured.• Isotope decay does not vary under various weathering conditions.• Isotopes decay at a fixed rate.• One isotope will decay into another isotope.

• The time of decay can be measured.• Isotope decay does not vary under various weathering conditions.• Isotopes decay at a fixed rate.• One isotope will decay into another isotope.

U238 (Uranium)

Pb206 (lead)

34

How does radiometric dating work, and where does theage (number) come from?

Half life: the time required for ½ of the parent to decay into the daughter element

Parent element: the “beginning” element that contains 100% of radioactive particles

Daughter element: the element that the parent element decays into (or turns into over time)

Parent Isotope

Stable Daughter Product

Currently Accepted Half-Life Values

Uranium-238 Lead-206 4.5 billion years

Uranium-235 Lead-207 704 million years

Thorium-232 Lead-208 14.0 billion years

Rubidium-87 Strontium-87 48.8 billion years

Potassium-40 Argon-40 1.25 billion years

Samarium-147 Neodymium-143 106 billion years

Terms:

35

U-3U-235 Pb 207

704 m.y.704 m.y.

1.4 b.y.1.4 b.y.

2.1 b.y.2.1 b.y.

1 half life = 704 million years

1/2 1/4 1/8

Daughterelement

Parentelement

36



11. Specifically define the differences 11. Specifically define the differences between relative and absolute dating between relative and absolute dating techniques.techniques.

12. Define the following absolute dating 12. Define the following absolute dating terms parent/daughter elements, half-lifeterms parent/daughter elements, half-life

13. Explain how the half-life is used to 13. Explain how the half-life is used to calculate an absolute age.calculate an absolute age.

37

What is the importance of radiometric dating?• produced thousands of dates for earth events

• rocks have been dated at more than 3 b.y.• granite in South Africa dated at 3.2 b.y.• granite contains inclusions of quartzite• quartzite inclusions must be older• Acasta gneiss in Northern Canada – 4.0 b.y.• Earth believed to be 4.55 (4.6) b.y. old

Radiometric dating:• vindicated the ideas of Hutton, Darwin, and others• consistent with relative dating techniques• allowed “absolute” dating on the Geologic Time Scale

38

Lets make a Geologic Time ScaleLets make a Geologic Time Scale

The Geologic Time Scale:• It combines both relative and absolute dating

• Created during the nineteenth century in Western Europe and Great Britain

• Sub-divides the 4.6 billion-year-history of the earth• Eons• Eras• Periods• Epochs

Relative dating + Absolute datingRelative dating + Absolute dating

39

Hadean• represents the earth’s time of formation• no rocks are represented• “hellish” conditions

Hadean• represents the earth’s time of formation• no rocks are represented• “hellish” conditions

Archean• Single cell life developed• most “ancient” rocks found• preserved rocks at the base of the Archean

Archean• Single cell life developed• most “ancient” rocks found• preserved rocks at the base of the Archean

Proterozoic• Multi-celled, soft body organisms• “early life”

Proterozoic• Multi-celled, soft body organisms• “early life”

Precambrian

Phanerozoic• “visible life”• fossil record becomes more detailed• animals have hard shells and skeletons

Phanerozoic• “visible life”• fossil record becomes more detailed• animals have hard shells and skeletons

Building the Geologic Time Scale

4040

Paleozoic Era• known as ancient life

• life progressed from marine invertebrates to fish, amphibians, and reptiles

Paleozoic Era• known as ancient life

• life progressed from marine invertebrates to fish, amphibians, and reptiles

Mesozoic Era• marks the rise in dinosaurs

• dominant vertebrates

• first flowering plants

• first shrew-like mammals

Mesozoic Era• marks the rise in dinosaurs

• dominant vertebrates

• first flowering plants

• first shrew-like mammals

Cenozoic Era• birds and mammals flourished

• appearance of man

Cenozoic Era• birds and mammals flourished

• appearance of man

41

Periods based on:

• fossil types• massive extinctions• geographical locations• characteristics of strata

Periods based on:

• fossil types• massive extinctions• geographical locations• characteristics of strata

Cambrian period• animals with hard shells• diversification of life “the Cambrian explosion”

Cambrian period• animals with hard shells• diversification of life “the Cambrian explosion”

Cretaceous, Jurassic, Triassic• age of reptiles• dinosaurs dominant• massive dinosaur extinction at 65 m.y. –Cretaceous• “Jurassic Park”

Cretaceous, Jurassic, Triassic• age of reptiles• dinosaurs dominant• massive dinosaur extinction at 65 m.y. –Cretaceous• “Jurassic Park”

42

Epochs

• not defined by extinction events, but % of fossils still living

• plants and animals found in the Pliocene epoch have living species today

• Eocene-few species surviving today

• Holocene• human’s time

Epochs

• not defined by extinction events, but % of fossils still living

• plants and animals found in the Pliocene epoch have living species today

• Eocene-few species surviving today

• Holocene• human’s time

Age ofReptiles

Amphibians

Age of fish

Invertebrates

How accurate is the Geologic Time Scale?How accurate is the Geologic Time Scale?

43

I I I I the Geologic Time Scale. the Geologic Time Scale. the Geologic Time Scale. the Geologic Time Scale. 14. You should be able to draw the 14. You should be able to draw the GeologicGeologic Time ScaleTime Scale and label it with the following: and label it with the following:

Eons, Eras, Periods, and Cenozoic/Eons, Eras, Periods, and Cenozoic/ Tertiary epochs.Tertiary epochs.

15. List major characteristics of each15. List major characteristics of each period.period.

16. How did the strength of both absolute and16. How did the strength of both absolute and relative dating techniques contribute therelative dating techniques contribute the development of the geologic time scale?development of the geologic time scale?

44

Cenozoic, Mesozoic, PaleozoicEras

The Geologic Time Scale – How much of Earth history isrepresented?

12%12%

Precambrian EonPrecambrian Eon88%88%

Geologic Time Scale

45

Difficulties in dating the Geologic Time ScaleDifficulties in dating the Geologic Time Scale

• Not all rocks can be dated radiometrically.Not all rocks can be dated radiometrically.• all minerals must contain 100% parent atoms.all minerals must contain 100% parent atoms.

• Sedimentary rocks can only rarely be dated.Sedimentary rocks can only rarely be dated.• some parent atoms come from pre-existing rockssome parent atoms come from pre-existing rocks that have been weathered and transported.that have been weathered and transported.• sedimentary rocks are dated in proximity of sedimentary rocks are dated in proximity of igneous bodies.igneous bodies.

• Metamorphic rocks are challenging.Metamorphic rocks are challenging.• some minerals do not necessarily represent thesome minerals do not necessarily represent the time when the rock was formedtime when the rock was formed

46

How is the age of the Earth determined?How is the age of the Earth determined?

Why is it difficult to determine the ageof the earth? (think rock cycle)

• The external and internal forces constantly recycle earth material, obliterating rock clues to the earth’s past.

Why is it difficult to determine the ageof the earth? (think rock cycle)

• The external and internal forces constantly recycle earth material, obliterating rock clues to the earth’s past.

What evidence suggests a 4.6 b.y. old earth?What evidence suggests a 4.6 b.y. old earth?• Precambrian rocks (Acasta gneiss, northern Canada) date at 4.0 billion years.

• Mineral grain found in sedimentary rock (Australia) dates at 4.4 billion years.

• What does the mineral grain in a sedimentary rock indicate about the 4.4 b.y. age relationship?

• Precambrian rocks (Acasta gneiss, northern Canada) date at 4.0 billion years.

• Mineral grain found in sedimentary rock (Australia) dates at 4.4 billion years.

• What does the mineral grain in a sedimentary rock indicate about the 4.4 b.y. age relationship?

47

Acasta gneiss, northern Canada• known as the Acasta gneiss complex

• dated at the Hadean Eon (4.0 billion years old)

• part of the Canadian Slave craton

Acasta gneiss, northern Canada• known as the Acasta gneiss complex

• dated at the Hadean Eon (4.0 billion years old)

• part of the Canadian Slave craton

48

Evidence from space to age date the earth--Evidence from space to age date the earth--moon dust and meteorites:

• moon dust from Apollo astronauts dated at 4.55 billion years

• the Allende Meteorite:

• a carbonaceous chondrite meteorite that was found in Chihuahua, Mexico, 1969

• contains unaltered material from the formation of the solar system

• composed of tiny amounts of carbon that form the compounds of amino acids (essential for life)

• age dating of this and other meteorites is around 4.55 billion years

• based on earth rocks and interstellar space objects, earth is believed to be around 4.6 billion years old.

moon dust and meteorites:• moon dust from Apollo astronauts dated at 4.55 billion years

• the Allende Meteorite:

• a carbonaceous chondrite meteorite that was found in Chihuahua, Mexico, 1969

• contains unaltered material from the formation of the solar system

• composed of tiny amounts of carbon that form the compounds of amino acids (essential for life)

• age dating of this and other meteorites is around 4.55 billion years

• based on earth rocks and interstellar space objects, earth is believed to be around 4.6 billion years old.49

Allende Meteorite, Chihuahua, Mexico, Feb. 8, 1969Allende Meteorite, Chihuahua, Mexico, Feb. 8, 1969

carbonaceous chondritecarbonaceous chondrite

• unaltered material from our solar system

• contains carbon (3 parts/1000)

• some carbon compounds in the form of amino acids

dark areas – olivine withtrace amounts of iron andcarbon

dark areas – olivine withtrace amounts of iron andcarbon

calcium and aluminum oxidecompounds

• first matter to form during solar system formation

• older than earth

calcium and aluminum oxidecompounds

• first matter to form during solar system formation

• older than earth50

I I I I what ES can do for me. what ES can do for me. what ES can do for me. what ES can do for me.


Discuss with a friend:Discuss with a friend:

17. Identify at least 2 problems with the17. Identify at least 2 problems with the accuracy of the Geologic Time Scale.accuracy of the Geologic Time Scale.

18. Why does the Geologic Time Scale only18. Why does the Geologic Time Scale only represent about 12% of the earth’s geologicrepresent about 12% of the earth’s geologic

history (assuming the earth is 4.6 b.y. old)? history (assuming the earth is 4.6 b.y. old)?

51