Transcript Chapter 13 Section 2 Paleozoic Era: Life Explodes

Chapter 13 Section 2
Paleozoic Era: Life Explodes
• Environmental changes that have affected
evolution on Earth:
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Formation & break up of continents
Mountain building
Volcanic activity
Changes in climate
Changes in sea level
• Mass extinction – when many types of living things
become extinct at the same time.
Cambrian Period
Many new groups of organisms evolved in a
relatively short period of time in an event called the
“Cambrian Explosion”
• Cambrian Earth
• Geologic changes contributed to Cambrian Explosion
• Supercontinent Rodinia broke up leaving many small
continents
• New environments formed in shallow seas between the
pieces of Rodinia
• Earth warmed coming out of an ice age
• Cambrian Life
• The number of different kinds of organisms increased
greatly in only 15 million years
• Cambrian organisms are well known because many
fossilized in the Burgess shale in the Canadian Rockies
• Most of these are several groups of invertebrates
(animals w/o backbones)
• Also had ancestors of vertebrates (animals w/backbones)
• Cambrian animals were first to evolve hard parts
• Shells for mollusks
• Arthropods evolved w/external skeleton of a protein called
chitin – modern arthropods include insects & crustaceans
• More than 600 types of trilobites evolved early in Cambrian
• Exoskeleton allows this scavenger to burrow through mud to find food
Ordovician Period
During Ordovician more complex
communities of organisms developed in the
oceans. First land dwelling plants evolved.
• Ordovician Earth
• Huge landmass of Gondwana was pushed south
• Gondwana was made of 5 of today’s continents –
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South America
Africa
Australia
Antarctica
Parts of Asia
Landmass collisions near equator made mountains in
eastern North America
• Ordovician Life
• Diversity of organisms in ocean increased
• Reef building invertebrates called bryozoans & early
corals evolved
• Trilobites were abundant
• Shelled organisms called brachiopods evolved
• Brachiopods – one of most widespread fossils of Paleozoic
• Vertebrates more common as jawless fish evolved
• Had bony, external covering
• Ancestors of later groups of fishes
• Evolution of land plants
• Small, primitive – such as liverworts
• Lived in moist areas & reproduced by spores
• Added oxygen to atmosphere
• Ice age caused mass extinction at end of Ordovician
Silurian Period
Time of reef building & evolution of fish. At the
end of this period plants & animals were becoming
widespread on land.
• Silurian Earth
• Main part of Gondwana was centered on South Pole
• In tropics, shallow seas covered plains of N. America
• Parts of continents can rise or sink below sea level if plates
upwarp or downwarp crust
• Some factors caused sea level to rise, flooding low-lying
areas
• Large barrier reef formed in these shallow seas
• Reefs restricted circulation between seas and open ocean
• Water evaporated leaving large quantities of rock salt &
gypsum
• Silurian Life
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Reef building corals evolved
Jawless fish survived developing thick armored plates
Jawed fish evolved
Strange looking arthropods appeared including eurypterids
– Land
• Small moss-like plants spread over moist low-lying areas
• Vascular plants evolved
– Vascular plants – plants with a stem containing thin tubes to carry
liquids within the plants
– These plants were leafless spikes about the size of an index finger
• Trace fossils showed arthropods were adapting to life on land
Devonian Period
Jawed fishes & sharks evolved. Plants, insects &
small arthropods colonized the land & amphibians
evolved.
• Devonian Earth
• Two large continents
• Gondwana occupied large part of s. hemisphere
• Laurasia, new large continent, formed in north included
• N. America
• Europe
• Parts of Asia
• Europe and N. America colliding formed what are now part
of the Appalachian Mountains
• Laurasia laid across the equator so western N. America had a
tropical climate & interior was hot & dry
• Devonian Life
– New types of jawed fishes w/bony skeletons
– Sharks w/cartilage skeletons
– Reefs formed by sponges & new types of coral
• Land plants
• First forests
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Large club mosses
Tree ferns
Horse tails
Fern-like plants cover ground
Wingless insects, spiders & centipedes
• Amphibians
• Four legged animal, w/lungs & can live on land, but lays eggs in
water
• Frogs, toads & salamanders are descendants
• Amphibians evolved from fishes
• Many types of amphibians evolved because they had no competition for
food
Carboniferous Period
The Carboniferous had great “coal swamp forests” in
wet, tropical areas. Amphibians & winged insects were
common and the first reptiles evolved.
• Carboniferous Earth
– Series of collisions between earth’s major landmasses
• Africa collides w/eastern edge of N. America
• This formed the southern Appalachian mountains
– Late in period landmasses began to merge to form the
supercontinent Pangaea
– Flat, low lying parts of continents flooded as sea levels
rose & fell
• Reef building organisms laid down huge deposits of calcium
carbonate
• Today these deposits form thick layers of limestone
• Carboniferous Life
– First reptiles
• Vertebrates with scaly skin that lays tough, leathery eggs that
can survive out of water
• Evolved from amphibians
• Could live in dry areas where amphibians could not live
– Vast swamps called coal swamp forests developed in wet
tropical areas
• Amphibians & winged insects lived in these swamps
• Plants & animals that died made thick layers that with time
(millions of years), pressure and heat made huge coal deposits
– Seed bearing plants evolved
• Adapted to drier areas
• Included first trees – a primitive type of conifer (cone bearing)
Permian Period
When the Permian Period began all the continents were joined to
form the supercontinent Pangaea. The evolution of life followed
the trends set by the Carboniferous. The Permian ended with the
greatest mass extinction in geologic history.
• Permian Earth
– Pangaea greatly changed earth’s environment
• Continental glaciers formed where Pangaea extended to the southern polar
region
• Ice ages ended as Pangaea drifted northward
• Warming trend
– Deserts formed in center of Pangaea
– Today huge deposits of red sandstone provide evidence of the deserts
• Many deserts dried up, however there were some in the southwestern U.S.
• Organic materials that built up from these seas, over millions of years
became oil deposits in West Texas and New Mexico
• Permian Life
– Life forms became more diverse on land & in ocean
• Conifers became more abundant
• New types of insects, amphibian, & reptiles evolved
• One type of reptiles was the mammal type reptiles
– The Permian Extinction
• 250 m.y.a. the Permian ended in a mass extinction
• Killed 96% of all species
– Ocean organisms that became extinct included most brachiopods, bryozoans &
all trilobites
– On land only a few mammal-like reptiles survived
• Cause of the extinction
– One hypothesis was that huge volcanic eruption in Siberia led to climate change
– Another hypothesis is a meteor struck in Antarctica making a weather change
and organisms could not adapt
– Another hypothesis for ocean organisms was that loss of coastline from the
formation of Pangaea made changes organisms could not adapt to