Geological Time ScalePaleontologists have divided Earth’s history into time units based on the life-forms that lived during certain periods

4 Major subdivisions:1. Eons

Longest subdivison Based upon abundance of

certain fossils

2. Eras 2nd longest subdivision Marked by worldwide change in

types of fossils present Ex: Mesozoic Era-many

invertebrates became extinct3. Periods

Characterized by the types of life existing worldwide

4. Epochs Smaller than periods Characterized by differences in life

forms

Organic EvolutionSpecies have changed over geologic timeEnvironmental changes can affect an

organism’s survivalThose that don’t adapt to changes are

less likely to surviveSpecies- group of organism that normally

reproduce only with other members of their group

Offspring of 2 different species can not reproduce (sterile)

Natural SelectionCharles Darwin proposed this theorySailed around the world gathering

informationIs a process by which organisms with

characteristics that are suited to a certain environment have a better chance of surviving and reproducing than organisms that do not have these characteristics

Organisms compete with each other for resources (food and living space)

Organisms in the same species can show variations-could help or hurt the organism’s chance of surviving

Organisms suited for their environment-lived longer and better chance of producing offspring

Organisms poorly adapted to environment-produced few or no offspring

A new characteristic becomes common in a species only if:some members already possess that

characteristicThat trait increases the animal’s chance

of survival

TrilobitesStructure of the hard outer skeleton or

exoskeleton3 lobes that run the length of the bodyBody made up of

Head-cephalonSegmented middle-thoraxTail-pygidiumFigure 7-Pg 397

Lived in Earth’s oceans for more than 200 million years

During Paleozoic Era, some species of trilobites became extinct and new ones evolved

Showed different characteristics during the different periods of the era

Trilobite eyes-changed over time, tell us about where they lived

Trilobite bodies-changed over time tooOlenellus had an extremely segmented

body compared to other trilobites, thought to be primitive

Plate TectonicsEarth’s moving plates caused continents to

collide and separate many timesCollisions caused mountains and closed seasPangaea-supercontinent when the continents

came together (end of Paleozoic Era)Separation of continents caused wider and

deeper seas trilobites lived in oceans and their

environment changed or was destroyedOnly one explanation of the extinction of

trilobites

Precambrian TimeLongest part of Earth’s historyIncludes the Hadean, Archean and

Proterozoic EonsLasted from 4.5 billions years ago to 544

million years agoLittle is known about this time because

rocks have been so deeply buried they have been changed by heat and pressure

Many fossils can’t stand these conditions

Earth was a lifeless planet with many volcanoes

Stromatolites-layered mats formed by cyanobacteria

Cyanobacteria-blue green algae; one of the earliest life forms on EarthFirst appeared 3.5 billion years agoContain chlorophyllUsed photosynthesisProduced O2 which helped change Earth’s

atmosphereO2 became a major atmospheric gasOzone layer began to form

Invertebrates appeared toward the end of Precambrian time

The production of O2 made it possible for single-celled organisms to evolve into more complex organisms

Many of these fossils are trace fossilsEdicaran animals

Bottom dwellersMight have had tough outer coveringsLooked like modern jellyfish, worms and

soft corals

Paleozoic EraOrganisms with hard parts mark the

beginning of this eraBegan about 544 million years agoEnded 248 million years agoWarm, shallow seas covered large

parts of continentsMany life forms during this time were

marineTrilobites presentFossils shows many animals had shells

Invertebrates not the only animalsVertebrates evolved during this eraFirst vertebrates were armoured fish-had

very powerful jawsBy the end of Devonian Period forests

appeared and vertebrates adapted to landMany ancient fish had lungs and gills-

enabled fish to live in low O2 leveled water

Paleontologists believe amphibians evolved from panderichthys- leglike fins and lungs

By the Pennsylvanian Period reptiles evolvedProduced egg with a membrane that

protected it from drying out-reproduction takes place away from water

Have skin with hard scale that prevent loss of body fluids

Many mountains formed during this eraEx: Appalachian Mountains1.Ocean separating North America from

Europe and Africa closed2.Collision of volcanic islands generated

mountains3.African plate collided with the North

American plate

At the end of the era:90% of all marine species died off70% of all land species died offPossible reasons are climate change and

lowering of sea levelPangaea formed closing seas and

creating mountainsOrganisms were unable to adapt to

these changesVolcanoes were very activeA large asteroid may have hit Earth

Mesozoic EraStarted 243 million years agoEnded 65 million years agoMarked by rapid movement of Earth’s

platesAll continents joined (Pangaea)

Separated into 2 large landmasses (Laurasia and Gondwanaland)

These 2 land masses continued to break apart into the present day continents

Reptiles became the largest group of animals on land by the Triassic period

First small dinosaurs appeared during Triassic period

Larger dinosaurs appeared during the Jurassic and Cretaceous periods

Fossils indicated some dinosaurs might have been warm-blooded and fast moving animals like present day mammals and birds

Fossils indicated some dinosaurs nurtured their young and traveled in herdsEx: Maiasaura

Birds appeared during the Jurassic periodPaleontologists believed birds evolved

from small, meat-eating dinosaursEarliest bird-ArchaeopteryxMammals first appeared in the Triassic

periodEarliest mammals resembled today’s

mouseWarm-blooded vertebrates and produce

milk to feed youngThese 2 characteristics enables mammals

to survive in many changing environments

Gymnosperms dominated the Mesozoic Era-are plants that produce seeds, but not flowersMany are still around today

Angiosperms (flowering plants) first evolved during the Cretaceous PeriodCan live in many environmentsMost diverse and abundant land plants

todayEx: magnolia and oak trees

Ended with a major extinction of land and marine speciesDinosaurs disappearedScientists believe an asteroid or

comet collided with Earth blocking out the sun

Plants and those organisms that depended on plants died out

The animals you see today and descendants of those who survived this mass extinction

Cenozoic EraEra of recent lifeBegan 65 million years agoLiving in this era todayMany mountain ranges in North

America, South America and Europe formed during the beginning of the era

Ice age occurredDivided into 2 periods-Tertiary

Period and Quaternary Period, which began 1.8million years ago

Alps in Europe formedAndes in South America formedHimalya formed while India moved

northward and collided with Asia (highest mountain on Earth)

Many kinds of mammals became largerAs Australia and South America

separated from Antarctica many species became isolated

Evolved separately from life-forms in other parts of the world

Evidence of this is marsupialsHomo sapiens appeared about 140,000

years agoAppearance of humans could have led to

the extinction of many other mammals