aim: how do we divide geologic time? geological time scale paleontologists have divided earth’s...
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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