Mesozoic Era 251 m.y.a 65.5 m.y · •because resources and space were readily available, an ... –iridium is commonly found in meteorites; very uncommon in Earth rocks. Mesozoic

Mesozoic Cenozoic notes.notebook

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Day 3Mesozoic & Cenozoic

Mesozoic & Cenozoic251 m.y.a Present

• at the end of the Permian, 90% of marine organisms and more than 70% of land organisms died.

• because resources and space were readily available, an abundance of new lifeforms appeared


Mesozoic Era251 m.y.a 65.5 m.y.a

• the geologic era that lasted from 251 million to 65.5 million years ago; called Age of Reptiles> lizards> turtles> crocodiles> snakes> dinosaurs

• Pangaea broke apart causes other collisions such as those that formed Sierra Nevada in California and Andes in South America

• climate was warm and humid; land covered mostly by shallow seas and marshes


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Triassic Period251 m.y.a 200 m.y.a

• dinosaurs appear• most were about 45 m long• lush forests of cycads (conebearing treeslike palm trees)• ichthyosaurs lived in oceans• ammonite is index fossil• first mammals (small rodents) appear


Jurassic Period200 m.y.a 146 m.y.a

• dinosaurs become dominant life forms> ornithischians "birdhipped"

– herbivores: stegosaurus– flying reptiles: pterosaurs

> saurischians "lizardhipped"– herbivores: apatosaurus were some of largest – carnivores


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Cretaceous Period146 m.y.a 65.5 m.y.a

• Tyrannosaurus rex: 6m tall and had huge jaws with teeth up to 15cm long

• ankylosaurs: armored; ceratopsians (horned), hadrosaurs (duckbilled)

• flowering plants, angiosperms, such as magnolias, willows, maples, oaks and walnuts became dominant


CretaceousTertiary Mass Extinction

• no dinosaur fossils have been found in rocks that formed after the Cretaceous

• some scientists believe changes in environment due to moving continents and increased volcanic activity were to blame

• Impact hypothesis: 65 million years ago, a giant meteorite crashed into Earth; raised enough dust to block the sun's rays for many yearscaused cooler climates, plants died and animals became extinct> dust formed a layer of iridiumladen rock

– iridium is commonly found in meteorites; very uncommon in Earth rocks


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Cenozoic Era65.5 m.y.a Present

• current geologic era, which began 65.5 million years ago; also called Age of Mammals

• continents moved to present day positions• huge mountain ranges such as Alps and Himalayas formed• temperatures decreased during ice ages, new species adapted to life in cooler climatesmammals become dominant

• divided into two periods: Tertiary (time before last ice age) and Quaternary (began with last ice age and includes present time)


Paleocene & Eocene Epochs65.5 m.y.a 33.9 m.y.a

• many small rodents evolved; first primates such as tarsier which is the sole modern survivor of earlier Paleocene

• ancestor of horse evolved during Eocene; first whales, flying squirrels and bats appeared

• small reptiles flourished• World wide temps. dropped by about 4o C by end of Eocene


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Oligocene & Miocene Epochs33.9 m.y.a 5.3 m.y.a

• Indian subcontinent began to collide with Eurasian continent, causing uplifting of Himalayas

• climate became drier and cooler; favors grasses and conebearing and hardwood trees

• most early mammals become extinct; large species of deer, pigs, horses, camels, cats and dogs flourish

• clams and snails continue to flourish• circumpolar currents form around Antarctica• late Miocene, Mediterranean Sea dries up and

refills several times• largest known land mammals exist

(sabertoothed cats)


Pliocene Epoch5.3 m.y.a 1.8 m.y.a

• predators evolved into modern forms (bear, dog & cat families)• herbivores such as giant ground sloth flourished• modern horses appear• Virginia State fossil, Chesapecten jeffersonius, was from this epoch• continental ice sheets begin to spread; sea level fell

> Bering land bridge appears between Eurasia and North America


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Pleistocene Epoch1.8 m.y.a 0.0115 m.y.a

• ice sheets advanced and retreated several times; animals had characteristics allowing them to endure cold (thick fur that covered wooly mammoths and wooly rhinoceroses)

• giant ground sloths and dire wolves became extinct• earliest modern human fossils were found in sedimentary rock of this epoch; cave paintings found suggest they were hunters


Holocene Epoch0.0115 m.y.a Present

• Began 11500 years ago as last glacial period ended• ice sheets melted and sea level rose about 140m, coastlines took on their present shapes and Great Lakes formed

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Mesozoic Era 251 m.y.a 65.5 m.y · •because resources and space were readily available, an ... –iridium is commonly found in meteorites; very uncommon in Earth rocks. Mesozoic