Earth HistoryEarth History

A. Geologic EventsA. Geologic Events

The history of the changing Earth is told in The history of the changing Earth is told in EarthEarth’’s s geologic eventsgeologic events..

The interpretation of these geologic events The interpretation of these geologic events is a form of is a form of puzzle solvingpuzzle solving ..

Earth HistoryEarth History

I.I. Fossils and Fossils and the Pastthe Past

a. A fossil is: a. A fossil is: the the remains or remains or the evidence the evidence of a living of a living thing, usually thing, usually preserved in preserved in rock.rock.

b. Formation of Fossils:b. Formation of Fossils:1. a. Most fossils are 1. a. Most fossils are incompleteincomplete because because usually usually only the hard parts of a plant or only the hard parts of a plant or animalanimal become fossils. become fossils.

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

2.2. a. Most fossils form a. Most fossils form when organisms when organisms are buried in sedimentsare buried in sediments..

b. Sediments often b. Sediments often harden and change harden and change into rockinto rock. When this happens, organisms . When this happens, organisms may be trapped in the rock. Most fossils may be trapped in the rock. Most fossils are found in are found in sedimentarysedimentary rocks. rocks.

Copy the steps in your notes for #1 - #6 according to the diagram!

FOSSIL FORMATION

Squid-like organism swimming in water.

Animal dies and is eaten by other animals or bacteria

Soft tissues quickly decompose leaving the

hard bones or shells behind

Over time sediment builds over the top and hardens into rock

As the encased bones decay, minerals seep in replacing the organic material cell by cell in a process called "petrification."

The void left behind may then fill with minerals making a stone replica of the organism.

Why are fossils seldom found in Why are fossils seldom found in other rock types?other rock types?

Fossils are almost never found in Fossils are almost never found in igneous igneous rocksrocks because magma is found deep within because magma is found deep within Earth where no living things exist, and lava at Earth where no living things exist, and lava at the surface of the Earth the surface of the Earth burns/melts burns/melts organismsorganisms before fossils can form. before fossils can form.

Fossils are rarely found in Fossils are rarely found in metamorphic metamorphic rocksrocks because because heat, pressure and/or heat, pressure and/or chemical activitychemical activity that causes a rock to that causes a rock to change, also destroys or damages fossils.change, also destroys or damages fossils.

c. Types of Fossilsc. Types of Fossils

1. 1. CastsCasts and and moldsmolds (in (in rock)rock)

2. 2. ImprintsImprints – occur when leaves and feathers – occur when leaves and feathers leave an impression in soft sediment (mud) that leave an impression in soft sediment (mud) that later hardens into rock.later hardens into rock.

3. 3. AmberAmber – occurs when insects are trapped and – occurs when insects are trapped and become embedded in resin (tree sap) that become embedded in resin (tree sap) that hardens. hardens. [4:30][4:30]

4. 4. IceIce – occurs when an organism – occurs when an organism is preserved in iceis preserved in ice.[4:00].[4:00]

5. 5. TarTar – occurs when animals are – occurs when animals are trapped in tar pits as at the LaBrea trapped in tar pits as at the LaBrea

Tar Pits of California.Tar Pits of California.

6. 6. PetrificationPetrification – occurs when minerals dissolved – occurs when minerals dissolved in ground water gradually replace the original in ground water gradually replace the original

tissues of plants and animals.tissues of plants and animals.

7. 7. Carbonaceous FilmCarbonaceous Film – occurs when the carbon – occurs when the carbon in the tissues of the organisms leave a residue of in the tissues of the organisms leave a residue of thin carbon on sediment which then hardens into thin carbon on sediment which then hardens into

rock.rock.

d. Interpreting Fossilsd. Interpreting Fossils

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

2. When fossils are arranged according to age, 2. When fossils are arranged according to age, they show that they show that certain living things have certain living things have changed or evolved over timechanged or evolved over time..

Trilobites

Isotelus - Ordovician

Dalmantes - Silurian

Calymene - Silurian

Phacops - Devonian

3. Fossils indicate how 3. Fossils indicate how the Earththe Earth’’s surface has s surface has changedchanged. For example, fossils of marine . For example, fossils of marine organisms can be found in rocks that are organisms can be found in rocks that are presently high above sea level.presently high above sea level.

Fossil Butte

•Green River Formation

•Eocene (50 myrs)

•Lake deposits

•Excellent fossil preservation

•fish, insects, reptiles, birds and mammals.

Phareodus

•Large Carniverous fish

•15 - 30 inches long

                                                      

4. Fossils give clues to 4. Fossils give clues to EarthEarth’’s past climates past climate

5. Fossils tell about the 5. Fossils tell about the appearance and appearance and activities of past life.activities of past life. For example, fossil teeth For example, fossil teeth give clues about the kind of food the animal ate.give clues about the kind of food the animal ate.

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II. Relative DatingII. Relative Dating

NO! Not that kind of relative dating!!

A.A. Relative Age – Relative Age – the the age of something age of something compared to compared to something elsesomething else..

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

c. Principle of Superposition – c. Principle of Superposition – In undisturbed In undisturbed sedimentary rock layers (strata), the oldest sedimentary rock layers (strata), the oldest

rock is at the bottom.rock is at the bottom.

Oldest

Youngest

D. Disturbed Rock Layers and Relative DatingD. Disturbed Rock Layers and Relative Dating

1. A fault is YOUNGER than the

rock layers it cuts across.

Rules of Relative Dating

2. An igneous intrusion is younger than the rock layers it penetrates.

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

4. Unconformity4. Unconformity

A "missing layer of A "missing layer of rock" or a gap in the rock" or a gap in the record. Simply put, record. Simply put, it is a "buried it is a "buried erosional surface."erosional surface." . .

In order for erosion to occur…….

UPLIFT had to happen first to put it at the surface!!!

What happened here?

E. Rock CorrelationE. Rock Correlation

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

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

2. Must have a wide distribution geographically.

•Preservable Parts (hard parts) •Limited time in existence as a species

•Widespread distribution (to correlate rocks that are far apart)

G. Volcanic time markers - G. Volcanic time markers - a layer of a layer of volcanic dust covering rocks over a large area volcanic dust covering rocks over a large area (maybe the world).(maybe the world).

When a violent eruption of a volcano occurs it When a violent eruption of a volcano occurs it may send dust high into the atmosphere where it may send dust high into the atmosphere where it can spread over the entire planet. It settles out can spread over the entire planet. It settles out of the air and forms a layer over wide regions at of the air and forms a layer over wide regions at the same time. the same time.

Asteroid impacts can have the same effect. Asteroid impacts can have the same effect. Example: the layer that marks the extinction of Example: the layer that marks the extinction of dinosaurs has characteristics of an asteroid dinosaurs has characteristics of an asteroid impact.impact.

III. Geologic TimeIII. Geologic Time

Up till now we have determined relative ages by: Up till now we have determined relative ages by: Superposition and Superposition and fossil recordfossil record Deformation and Deformation and unconformitiesunconformities Cross-cutting relationshipsCross-cutting relationships

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

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B. Geologic time began when Earth first formed about 4,600 million years ago or 4.6 billion years ago.

C. The units or sections of geologic time include:C. The units or sections of geologic time include:

1.1. EONEON– largest division of Earth history– largest division of Earth history

Relative time scale started to be established in the 19Relative time scale started to be established in the 19 thth century. century.

Hadean eonHadean eon: Establishment of core, plate tectonic system and : Establishment of core, plate tectonic system and climate (climate (3.8 – 4.6 bya3.8 – 4.6 bya))

Archean eonArchean eon: earth oldest rocks were found. Core of continents : earth oldest rocks were found. Core of continents are formed, unicellular organisms originated. (are formed, unicellular organisms originated. (2.5 – 3.8 bya2.5 – 3.8 bya))

Proterozoic eonProterozoic eon: plate tectonic and climate geosystems became : plate tectonic and climate geosystems became similar to present day. Oxygen in the atmosphere established similar to present day. Oxygen in the atmosphere established resulting in iron formations, multicellular organism developed in resulting in iron formations, multicellular organism developed in later record. (later record. (540 mya – 2.5 bya540 mya – 2.5 bya))

Phanerozoic eonPhanerozoic eon: abundant life and multicellular organisms, rich : abundant life and multicellular organisms, rich fossil record (fossil record (540 mya – present540 mya – present))

2. Era – subdivisions of an eon

3. Period – subdivision of an era

4. Epoch – subdivisions of a period

Phanerozoic Eon is divided into 3 eras:

Paleozoic (old life)

Mesozoic (middle life)

Cenozoic (recent life)

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

1.1. Major extinctionsMajor extinctions – Ex: Cretaceous and – Ex: Cretaceous and Tertiary Period boundary – Dinosaurs Tertiary Period boundary – Dinosaurs become extinctbecome extinct

2.2. Appearance of a new life form Appearance of a new life form

3.3. Major climate changesMajor climate changes – – Ex: boundary Ex: boundary between Pleistocene and Holocene between Pleistocene and Holocene Epochs marked by last major ice age.Epochs marked by last major ice age.

Soft-bodied organisms

Emergence of vertebrates

Major extinction ~90% of life

Major Extinction

~ 50% of life

IV. Absolute Age – IV. Absolute Age – identifies the exact identifies the exact

date of an eventdate of an event..

A.A. RadioactivityRadioactivity – the ability of an element – the ability of an element to change spontaneously into a different to change spontaneously into a different element by element by losing or gaining matterlosing or gaining matter from the nucleus of an atom.from the nucleus of an atom.

B. Radioactive DecayB. Radioactive Decay

1.1. Radioactive or ParentRadioactive or Parent element = an element = an atom that has an unstable nucleus that atom that has an unstable nucleus that changes spontaneously or changes spontaneously or ““decaysdecays””..

2.2. Decay or DaughterDecay or Daughter element = the stable element = the stable element that is the result of the element that is the result of the spontaneous change in a radioactive spontaneous change in a radioactive element.element.

3.3. Half-life = Half-life = the time it takes for ½ of a the time it takes for ½ of a radioactive element to change into a radioactive element to change into a decay or stable element.decay or stable element.

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

1.1. HeatHeat2.2. PressurePressure3.3. Chemical actionChemical action

Key points of Radioactive Decay:Key points of Radioactive Decay: A ratio between the original material (parent A ratio between the original material (parent

material) and the decay product (daughter material) and the decay product (daughter material) can be used to determine how many material) can be used to determine how many half-lives the material has undergone. half-lives the material has undergone.

The radioisotope used should have a half - life The radioisotope used should have a half - life that is around the age of the object being dated. that is around the age of the object being dated. Ex: C14 is used for objects thousands of years old Ex: C14 is used for objects thousands of years old C14 can be used to date back to around 50,000 years. C14 can be used to date back to around 50,000 years.

5. Carbon 14 has a short half-life and is therefore used to date the remains of living things such as wood, bones, leather.

V. Evolutionary DevelopmentV. Evolutionary Development

1.1. SpeciesSpecies – organisms that are able to mate – organisms that are able to mate and produce offspring capable of continuing and produce offspring capable of continuing the same species.the same species.

2.2. Organic evolutionOrganic evolution – suggests that variations – suggests that variations within a species may provide some members within a species may provide some members of that species with a higher probability of of that species with a higher probability of survivalsurvival

3.3. Rock record indicates that Rock record indicates that older rockolder rock formations contain more simple and marine life formations contain more simple and marine life forms, while the forms, while the younger rock formationsyounger rock formations have more complex organisms.have more complex organisms.

Early HominidsEarly Hominids

Unlike Man – some organisms have

changed little in their design, like sharks!