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Earth’s Past
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The Geologic Time ScaleEarth’s history is divided different sections
of time The sections are determined by the living
things and the rock recordThe geologic time scale is broken up into
eons, eras, periods, and sometimes epochs
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Epochs – Divide
periods
Periods – Divide eras
Eras – Divide eons
Eons – Longest segment
of geologic time
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ChangesEarth has changed dramatically over timeEarth atmosphere initially comprised of
CO2, Sulfur Dioxide, Water Vapor, and Nitrogen
Liquid Oceans DevelopedOxygen (O2) entered the atmosphere with
the appearance of photosynthetic organisms, such as algae
Living things have evolved and mass extinctions have occurred
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EvolutionSince appearing on Earth, animals and plants
have been changing in appearance, size, and structure
This change is called evolution.In the 1800’s, Charles Darwin called the
process of the species that survive due to traits better suited to the environment natural selection
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The Precambrian (4.5-543 mya)
Precambrian time includes all geologic time before the Cambrian period in the Paleozoic era.
This is the combination of the Hadean ArcheanProterozoic
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The PrecambrianHadean●Archean●ProterozoicHadean Eon
The Formation of EarthMeteor ImpactsNo LifeVolcanic ActivityFormation of Early AtmosphereCooling of Water Vapor to Form Oceans
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The PrecambrianHadean●Archean●ProterozoicArchean Eon (3.8-2.5 bya)
Started with the formation of the crust and first rocks (3.8 bya)
The Cratons are the oldest Archean
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The PrecambrianHadean●Archean●ProterozoicThe first evidence of life
is found in Archean rocks Simple bacteria (3.8
bya)Cyanobacteria – simple
single celled organisms (3.5 bya) Trapped in sediment they
form structures called stromatolites
Photosynthesis began ~3 bya
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The PrecambrianHadean●Archean●Proterozoic
Proterozoic Eon (2.5 bya -543 mya)
Abundant volcanic activity
No life on landAll organisms had
soft bodiesMulticellular life
began (2.1 bya)Taxa such as
jellyfish and worms appear at the end of the Proterozoic (1 bya)
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Paleozoic Era (543-290 mya)
This era is the beginning of an abundant fossil record
It is broken up into six periodsCambrianOrdovicianSilurianDevonianCarboniferousPermian
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PaleozoicCambrian●Ordovician●Silurian●Devonian● Carboniferous●PermianCambrian Period (543-490mya)
The most commonly preserved Cambrian animal is the trilobite, a crablike invertebrate.
Very little mountain building Warm oceansAll life in waterCambrian ExplosionHard Shells evolved leaving a
better fossil record
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PaleozoicCambrian●Ordovician●Silurian●Devonian● Carboniferous●Permian
Ordovician Period (490-443mya)The graptolite is a useful
index fossil of the Ordovician.
Appalachian Mountains formed as tectonic plates crashed into one another
All life in water
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PaleozoicCambrian●Ordovician●Silurian●Devonian● Carboniferous●Permian
Silurian Period (443-417 mya)The eurypterid is sometimes
called a sea scorpion is a good index fossil .
Evolution of terrestrial (land)The first land animals
included distant relatives of spiders, millipedes, and scorpions.
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The geologic time scale is broken up into…
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1. Centuries, scores, decades, years, and months
2. Eons, eras, periods, and sometimes epochs
3. Units4. Pounds and ounces
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Which statement is true?
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1. An epoch is bigger than a period
2. An era is bigger than an eon
3. An epoch is bigger than an eon
4. An era is bigger than a period
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What gave the earth the great majority of its oxygen in the atmosphere?
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1. Aliens2. Pollution3. Plants like algae4. Comets5. It was there in the
first place
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What is evolution?
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1. Mass extinction of plants and/or animals
2. Plants/animals changing and adapting to better suit their environment
3. A time period4. An awesome band
name \m/
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What is the oldest time period in Earth’s history?
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1. Proterozoic2. Archean3. Hadean4. Jurassic5. Cretaceous
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When was the first evidence of life found?
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1. Proterozoic2. Archean3. Hadean4. Jurassic5. Cretaceous6. Silurian
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When was the first evidence of life on land found?
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1. Proterozoic2. Archean3. Hadean4. Jurassic5. Cretaceous6. Silurian
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PaleozoicCambrian●Ordovician●Silurian●Devonian● Carboniferous●Permian
Devonian Period (417-354 mya)“Age of the Fish”Lung fish first appeared
(ancestor to amphibians)First appearance of
forests consisting of ferns, giant rushes, and primitive conifers.
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PaleozoicCambrian●Ordovician●Silurian●Devonian● Carboniferous●Permian
Carboniferous PeriodAKA: Mississippian and
Pennsylvanian PeriodsMississippian Period:Crinoids, which look
like plants, are actually invertebrate animals related to sea stars.
Foraminifera are one-celled organisms with tiny calcite shells.
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PaleozoicCambrian●Ordovician●Silurian●Devonian● Carboniferous●Permian
Pennsylvanian PeriodFirst appearance of
reptiles, the first true land vertebrates (with backbone)
Large insects including early ancestors of the cockroach
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PaleozoicCambrian●Ordovician●Silurian●Devonian● Carboniferous●Permian
Permian PeriodDry climateWidespread mountain building caused by continental
collisionsMass extinction ended the period and the Paleozoic EraMarine cephalopods and reptiles were among the survivors
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Mesozoic Era (248-65 mya)The Mesozoic Era “Age of the Reptiles”
Triassic PeriodJurassic PeriodCretaceous Period
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MesozoicTriassic●Jurassic●Cretaceous
Triassic Period (248-206 mya)Dinosaurs made their
first appearance on land.Some of the first
dinosaurs were about the size of a cat.
Cephalopods called ammonites are an important index fossil.
During most of the Triassic, almost all of Earth’s land was joined as the supercontinent Pangaea.
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MesozoicTriassic●Jurassic●Cretaceous
Jurassic PeriodMany larger
dinosaurs, including brachiosaurus and Allosaurus
Morphing insects like flies and caterpillars appeared
First birds appeared
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MesozoicTriassic●Jurassic●Cretaceous
Cretaceous PeriodThe largest dinosaurs
lived during this period, often exceeding 25 meters in length. (T-rex, Brachiosaurs)
The appearance of flowering plants is perhaps the greatest event.
Modern trees developed. Ex. oak, maple, birch.
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MesozoicTriassic●Jurassic●CretaceousContinents appeared much
as they do today.Evidence supports asteroid
collision caused mass extinction at end of period
This ended the Mesozoic Era (183 million years of dinosaur domination)
Mammals survived the mass extinction
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Cenozoic Era (65 mya -present)
Regarded as Earth’s recent history“The Age of the Mammals”Divided into three periods:
PaleogeneNeogeneQuaternary
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CenozoicPaleogene●Neogene●Quaternary
Paleogene PeriodModern Mountain
Ranges:Rockies, the Alps, Himalayas,
Introduction of mammals
Global climate cooled
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CenozoicPaleogene●Neogene●QuaternaryNeogene Period
Appearance of grasses lead to explosion of grazing animals such as sheep and cows
Modern forms of the horse, camel, and elephant debuted here
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CenozoicPaleogene●Neogene●Quaternary
Quaternary PeriodGreat temperature fluctuations from
warm to cold, leading to increased rates of extinction and evolution
First appearance of humans
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What period did crinoids appear?
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1. Cambrian2. Ordovician3. Silurian4. Devonian5. Carboniferous6. Permian
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What period did reptiles first appear?
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1. Cambrian2. Ordovician3. Silurian4. Devonian5. Carboniferous6. Permian
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What period did forests appear on land?
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1. Cambrian2. Ordovician3. Silurian4. Devonian5. Carboniferous6. Permian
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What was the Mesozoic Era most known for?
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1. First appearance of life
2. First appearance of oxygen in the atmosphere
3. First appearance of land dinosaurs
4. First appearance of humans
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Which period saw the largest dinosaurs?
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1. Cambrian2. Ordovician3. Silurian4. Triassic5. Jurassic6. Cretaceous7. Hadean8. Mississippian
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What period did mammals first appear?
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1. Paleogene2. Neogene3. Quaternary4. Triassic5. Jurassic6. Cretaceous7. Hadean8. Mississippian
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What period did humans first appear?
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1. Paleogene2. Neogene3. Quaternary4. Triassic5. Jurassic6. Cretaceous7. Hadean8. Mississippian