Geologic time is divided into eons, eras, periods, and epochs based on fossils and lifeforms. The document then discusses evolution, natural selection, trilobites from the Ordovician Period, Precambrian life like cyanobacteria, the Paleozoic Era which saw evolution of amphibians and reptiles, the Mesozoic Era of dinosaurs and the rise of mammals and flowering plants, and the ongoing Cenozoic Era of continuing mammalian evolution and the emergence of humans.

1. Geologic TimeGeologic Time

2. Geologic TimeGeologic Time
 Geologic Time – Earth’s history dividedGeologic Time – Earth’s history divided
into time units that make up a geologic timeinto time units that make up a geologic time
scalescale
 Time units on the scale are based on theTime units on the scale are based on the
appearance or disappearance of types ofappearance or disappearance of types of
organisms such as trilobites, index fossils thatorganisms such as trilobites, index fossils that
lived during specific time periodslived during specific time periods

3. Geologic TimeGeologic Time
 Geologic time is divided into four majorGeologic time is divided into four major
subdivisionssubdivisions
 EonsEons – longest subdivision; based on abundance of– longest subdivision; based on abundance of
fossilsfossils
 ErasEras – marked by significant worldwide changes in the– marked by significant worldwide changes in the
types of fossils present in rocktypes of fossils present in rock
 PeriodsPeriods – based on types of life existing worldwide at a– based on types of life existing worldwide at a
particular timeparticular time
 EpochsEpochs – characterized by differences in life-forms, but– characterized by differences in life-forms, but
differences can be regional rather than globaldifferences can be regional rather than global

4. EvolutionEvolution
 OrganicOrganic evolution – organisms have changed overevolution – organisms have changed over
time, most likely because of environmentaltime, most likely because of environmental
changeschanges
 SpeciesSpecies – organisms that normally reproduce only with– organisms that normally reproduce only with
other members of their groupother members of their group
 Darwin’s theory ofDarwin’s theory of natural selectionnatural selection – organisms more– organisms more
adapted to an environment are more likely toadapted to an environment are more likely to
reproducereproduce
 Natural selection within a species occurs only ifNatural selection within a species occurs only if
characteristics present in some numbers increase theircharacteristics present in some numbers increase their
survivalsurvival
 ArtificialArtificial selection – breeding individuals with desiredselection – breeding individuals with desired
characteristics; humans use this type of selection whencharacteristics; humans use this type of selection when
breeding domestic animalsbreeding domestic animals
 NewNew species can evolve from natural selectionspecies can evolve from natural selection

5. Ordovician Period 485-444 mya
Volkhov River, Russia

6. TrilobitesTrilobites
 Trilobites – have an exoskeleton with three lobes;Trilobites – have an exoskeleton with three lobes;
lived in oceans for more than 200 million yearslived in oceans for more than 200 million years
 TrilobiteTrilobite eyeeye position changed as the species adapted toposition changed as the species adapted to
various environmentsvarious environments
 Trilobite bodies andTrilobite bodies and tailstails changed in response tochanged in response to
changing environmentschanging environments
 Continental collisions formed the giant landmassContinental collisions formed the giant landmass
PangeaPangea near the end of the Paleozoic Era. Thesenear the end of the Paleozoic Era. These
collisions may have dropped sea levels, causing thecollisions may have dropped sea levels, causing the
extinction of trilobites.extinction of trilobites.

7. Precambrian TimePrecambrian Time
 4 billion to about 544 million years ago4 billion to about 544 million years ago
 Very few fossils remainVery few fossils remain
 Precambrian rocks are deeply buried causingPrecambrian rocks are deeply buried causing
the fossils to be changed by heat and pressurethe fossils to be changed by heat and pressure
 Most Precambrian organisms lacked hard partsMost Precambrian organisms lacked hard parts
 Cyanobacteria are blue-green algeaCyanobacteria are blue-green algea
 One of earliest life forms to appearOne of earliest life forms to appear
 Added oxygen to atmosphere throughAdded oxygen to atmosphere through
photosynthesisphotosynthesis
 Invertebrates and Ediacaran animalsInvertebrates and Ediacaran animals
appeared late in Precambrian timeappeared late in Precambrian time

9. Paleozoic EraPaleozoic Era
 544 million years ago to about 245 million years544 million years ago to about 245 million years
agoago
 Many organisms with shells and vertebratesMany organisms with shells and vertebrates
evolved in the warm, shallow seaevolved in the warm, shallow sea
 Amphibians evolved to survive in water and onAmphibians evolved to survive in water and on
landland
 Might have evolved from fishMight have evolved from fish
 Could obtain oxygen from gills or lungsCould obtain oxygen from gills or lungs
 Reptiles evolved from amphibians to surviveReptiles evolved from amphibians to survive
farther from waterfarther from water
 Several mountain-building episodes occurredSeveral mountain-building episodes occurred
 Most marine and land species became extinct atMost marine and land species became extinct at
the endthe end

11. Mesozoic EraMesozoic Era
 245 to 65 million years ago245 to 65 million years ago
 Pangea separated into continents and climate became drierPangea separated into continents and climate became drier
 Dinosaurs evolved; they might have been warm-blooded,Dinosaurs evolved; they might have been warm-blooded,
traveled in herds, and nurtured their youngtraveled in herds, and nurtured their young
 Birds, which probably evolved from meat-eatingBirds, which probably evolved from meat-eating
dinosaurs, appeared during the Jurassic Perioddinosaurs, appeared during the Jurassic Period
 Small, mouse-like mammals, warm-blooded vertebratesSmall, mouse-like mammals, warm-blooded vertebrates
with hair and milk to feed their young appear in Triassicwith hair and milk to feed their young appear in Triassic
PeriodPeriod
 Angiosperms, flowering plants, appeared during theAngiosperms, flowering plants, appeared during the
Cretaceous PeriodCretaceous Period
 A great extinction, perhaps caused by a comet or asteroidA great extinction, perhaps caused by a comet or asteroid
collision, occurred about 65 million years ago, marking thecollision, occurred about 65 million years ago, marking the
end of the Mesozoic Eraend of the Mesozoic Era

13. Cenozoic EraCenozoic Era
 65 million years ago and continues today65 million years ago and continues today
 Many mountain ranges formed, perhapsMany mountain ranges formed, perhaps
creating cooler climates worldwidecreating cooler climates worldwide
 Mammals continued to evolvedMammals continued to evolved
 Many species became isolated as the continentsMany species became isolated as the continents
continued to separatecontinued to separate
 Homo sapiensHomo sapiens, or humans, appeared about, or humans, appeared about
400,000 years ago400,000 years ago