Chapter 13 Section 2 Paleozoic Era: Life Explodes Environmental changes that have affected evolution on Earth: 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 Cambrian Earth 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 Ordovician Earth 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 – 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 Silurian Earth 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 Ocean Land 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 Devonian Earth 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 Land plants Amphibians New types of jawed fishes w/bony skeletons Sharks w/cartilage skeletons Reefs formed by sponges & new types of coral Land plants First forests 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 Two mass extinctions occurred during the last of the Devonian, the first affecting mainly ocean organisms

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 Permian Earth 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