Geologic TimeGeologic Time

Geologic TimeGeologic Time

Geologic Time – Earth’s history divided Geologic Time – Earth’s history divided into time units that make up a geologic time into time units that make up a geologic time scalescale Time units on the scale are based on the Time units on the scale are based on the

appearance or disappearance of types of appearance or disappearance of types of organisms such as trilobites, index fossils that organisms such as trilobites, index fossils that lived during specific time periodslived during specific time periods

Geologic TimeGeologic Time

Geologic time is divided into four major Geologic 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

EvolutionEvolution OrganicOrganic evolution – organisms have changed over evolution – organisms have changed over

time, most likely because of environmental time, 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 of Darwin’s theory of natural selectionnatural selection – organisms more – organisms more

adapted to an environment are more likely to adapted to an environment are more likely to reproducereproduce

Natural selection within a species occurs only if Natural selection within a species occurs only if characteristics present in some numbers increase their characteristics present in some numbers increase their survivalsurvival

ArtificialArtificial selection – breeding individuals with desired selection – breeding individuals with desired characteristics; humans use this type of selection when characteristics; humans use this type of selection when breeding domestic animalsbreeding domestic animals

NewNew species can evolve from natural selection species can evolve from natural selection

Ordovician Period 485-444 myaVolkhov River, Russia

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 Trilobite Trilobite eyeeye position changed as the species adapted to position changed as the species adapted to

various environmentsvarious environments Trilobite bodies and Trilobite bodies and tailstails changed in response to changed in response to

changing environmentschanging environments Continental collisions formed the giant landmass Continental collisions formed the giant landmass

PangeaPangea near the end of the Paleozoic Era. These near the end of the Paleozoic Era. These collisions may have dropped sea levels, causing the collisions may have dropped sea levels, causing the extinction of trilobites.extinction of trilobites.

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 causing Precambrian 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 through Added oxygen to atmosphere through

photosynthesisphotosynthesis Invertebrates and Ediacaran animals Invertebrates and Ediacaran animals

appeared late in Precambrian timeappeared late in Precambrian time

Paleozoic EraPaleozoic Era 544 million years ago to about 245 million years 544 million years ago to about 245 million years

agoago Many organisms with shells and vertebrates Many organisms with shells and vertebrates

evolved in the warm, shallow seaevolved in the warm, shallow sea Amphibians evolved to survive in water and on Amphibians 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 survive Reptiles 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 at Most marine and land species became extinct at

the endthe end

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-eating Birds, which probably evolved from meat-eating

dinosaurs, appeared during the Jurassic Perioddinosaurs, appeared during the Jurassic Period Small, mouse-like mammals, warm-blooded vertebrates Small, mouse-like mammals, warm-blooded vertebrates

with hair and milk to feed their young appear in Triassic with hair and milk to feed their young appear in Triassic PeriodPeriod

Angiosperms, flowering plants, appeared during the Angiosperms, flowering plants, appeared during the Cretaceous PeriodCretaceous Period

A great extinction, perhaps caused by a comet or asteroid A great extinction, perhaps caused by a comet or asteroid collision, occurred about 65 million years ago, marking the collision, occurred about 65 million years ago, marking the end of the Mesozoic Eraend of the Mesozoic Era

Cenozoic EraCenozoic Era

65 million years ago and continues today65 million years ago and continues today Many mountain ranges formed, perhaps Many mountain ranges formed, perhaps

creating cooler climates worldwidecreating cooler climates worldwide Mammals continued to evolvedMammals continued to evolved

Many species became isolated as the continents Many 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