A. Geologic EventsA. Geologic Events
The history of the changing Earth is told inThe history of the changing Earth is told in
EarthEarth’s’s geologic eventsgeologic events..
The interpretation of these geologic eventsThe interpretation of these geologic events
is a form ofis a form of puzzle solvingpuzzle solving ..
Earth HistoryEarth History
I.I. Fossils andFossils and
the Pastthe Past
a. A fossil is:a. A fossil is: thethe
remains orremains or
the evidencethe evidence
of a livingof a living
thing, usuallything, usually
preserved inpreserved in
b. Formation of Fossils:b. Formation of Fossils:
1. a. Most fossils are1. a. Most fossils are incompleteincomplete becausebecause
usuallyusually only the hard parts of a plant oronly the hard parts of a plant or
animalanimal become fossils.become fossils.
b.b. The soft flesh of deadThe soft flesh of dead
organisms was usually eatenorganisms was usually eaten
by animals or decayed beforeby animals or decayed before
it could form into a fossil.it could form into a fossil.
2.2. a. Most fossils forma. Most fossils form when organismswhen organisms
are buried in sedimentsare buried in sediments..
b. Sediments oftenb. Sediments often harden and changeharden and change
into rockinto rock. When this happens, organisms. When this happens, organisms
may be trapped in the rock. Most fossilsmay be trapped in the rock. Most fossils
are found inare found in sedimentarysedimentary rocks.rocks.
Copy the steps in your notes for
#1 - #6 according to the diagram!
swimming in water.
Animal dies and is
eaten by other
animals or bacteria
Soft tissues quickly
decompose leaving the
hard bones or shells
Over time sediment builds
over the top and hardens
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
Why are fossils seldom found inWhy are fossils seldom found in
other rock types?other rock types?
Fossils are almost never found inFossils are almost never found in igneousigneous
rocksrocks because magma is found deep withinbecause magma is found deep within
Earth where no living things exist, and lava atEarth where no living things exist, and lava at
the surface of the Earththe surface of the Earth burns/meltsburns/melts
organismsorganisms before fossils can form.before fossils can form.
Fossils are rarely found inFossils are rarely found in metamorphicmetamorphic
rocksrocks becausebecause heat, pressure and/orheat, pressure and/or
chemical activitychemical activity that causes a rock tothat 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 andand
2.2. ImprintsImprints – occur when leaves and feathers– occur when leaves and feathers
leave an impression in soft sediment (mud) thatleave 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) thatbecome embedded in resin (tree sap) that
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 LaBreatrapped 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 originalin 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 ofin the tissues of the organisms leave a residue of
thin carbon on sediment which then hardens intothin carbon on sediment which then hardens into
d. Interpreting Fossilsd. Interpreting Fossils
1. Fossils indicate that1. Fossils indicate that
many different kindsmany different kinds
of life forms existedof life forms existed
at different times inat 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 thatthey show that certain living things havecertain living things have
changed or evolved over timechanged or evolved over time..
3. Fossils indicate how3. 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 areorganisms can be found in rocks that are
presently high above sea level.presently high above sea level.
•Green River Formation
•Eocene (50 myrs)
•Excellent fossil preservation
•fish, insects, reptiles, birds
•Large Carniverous fish
•15 - 30 inches long
4. Fossils give clues to4. Fossils give clues to
EarthEarth’s past climate’s past climate
5. Fossils tell about the5. Fossils tell about the appearance andappearance and
activities of past life.activities of past life. For example, fossil teethFor example, fossil teeth
give clues about the kind of food the animal ate.give clues about the kind of food the animal ate.
II. Relative DatingII. Relative Dating
NO! Not that kind of
A.A. Relative Age –Relative Age – thethe
age of somethingage of something
compared tocompared to
something elsesomething else..
B.B. The GeologicThe Geologic
ColumnColumn – an ideal– an ideal
sequence of rocksequence of rock
layers created bylayers created by
combining data fromcombining data from
all known rockall known rock
sequences at varioussequences at various
c. Principle of Superposition –c. Principle of Superposition – In undisturbedIn undisturbed
sedimentary rock layers (strata), the oldestsedimentary rock layers (strata), the oldest
rock is at the bottom.rock is at the bottom.
D. Disturbed Rock Layers and Relative DatingD. Disturbed Rock Layers and Relative Dating
1. A fault is
YOUNGER than the
rock layers it cuts
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 ofA "missing layer of
rock" or a gap in therock" or a gap in the
record. Simply put,record. Simply put,
it is a "buriedit is a "buried
erosional surface."erosional surface." ..
In order for erosion to
UPLIFT had to happen first
to put it at the surface!!!
F. Index Fossils –F. Index Fossils – a fossil that is used to datea 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
2. Must have a
•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 ofa layer of
volcanic dust covering rocks over a large areavolcanic dust covering rocks over a large area
(maybe the world).(maybe the world).
When a violent eruption of a volcano occurs itWhen a violent eruption of a volcano occurs it
may send dust high into the atmosphere where itmay send dust high into the atmosphere where it
can spread over the entire planet. It settles outcan spread over the entire planet. It settles out
of the air and forms a layer over wide regions atof 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 ofExample: the layer that marks the extinction of
dinosaurs has characteristics of an asteroiddinosaurs has characteristics of an asteroid
III. Geologic TimeIII. Geologic Time
Up till now we have determined relative ages by:Up till now we have determined relative ages by:
Superposition andSuperposition and fossil recordfossil record
Deformation andDeformation and unconformitiesunconformities
Cross-cutting relationshipsCross-cutting relationships
A.A. TheThe Geologic Time ScaleGeologic Time Scale divides Earthdivides Earth’s’s
history into sections of time.history into sections of time.
B. Geologic time began when Earth first formed
about 4,600 million years ago or 4.6 billion
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 19thth
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 establishedsimilar to present day. Oxygen in the atmosphere established
resulting in iron formations, multicellular organism developed inresulting 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 intervalsD. 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 – DinosaursTertiary Period boundary – Dinosaurs
become extinctbecome extinct
2.2. Appearance of a new life formAppearance of a new life form
3.3. Major climate changesMajor climate changes –– Ex: boundaryEx: boundary
between Pleistocene and Holocenebetween Pleistocene and Holocene
Epochs marked by last major ice age.Epochs marked by last major ice age.
~90% of life
~ 50% of life
IV. Absolute Age –IV. Absolute Age – identifies the exactidentifies 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 differentto change spontaneously into a different
element byelement 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 = anelement = an
atom that has an unstable nucleus thatatom that has an unstable nucleus that
changes spontaneously orchanges spontaneously or “decays”.“decays”.
2.2. Decay or DaughterDecay or Daughter element = the stableelement = the stable
element that is the result of theelement that is the result of the
spontaneous change in a radioactivespontaneous change in a radioactive
3.3. Half-life =Half-life = the time it takes for ½ of athe time it takes for ½ of a
radioactive element to change into aradioactive element to change into a
decay or stable element.decay or stable element.
4.4. The rate of decay (half-life) is NOTThe rate of decay (half-life) is NOT
affected by any outside condition suchaffected by any outside condition such
3.3. Chemical actionChemical action
Key points of Radioactive Decay:Key points of Radioactive Decay:
A ratio between the original material (parentA ratio between the original material (parent
material) and the decay product (daughtermaterial) and the decay product (daughter
material) can be used to determine how manymaterial) 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 - lifeThe 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 oldEx: 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,
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 continuingand 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 memberswithin a species may provide some members
of that species with a higher probability ofof that species with a higher probability of
3.3. Rock record indicates thatRock record indicates that older rockolder rock
formations contain more simple and marine lifeformations contain more simple and marine life
forms, while theforms, while the younger rock formationsyounger rock formations
have more complex organisms.have more complex organisms.