CHAPTER 9 A VIEW OF EARTH’S PAST
III. THE MESOZOIC AND CENOZOIC ERAS
- 90% of marine and 70% of land organisms died at the end of the
Permian Period
- mass extinction – an episode during which large numbers of species
extinct
- an abundance of new life forms appeared
A. The Mesozoic Era
1. began 251 million years ago and ended 65 million years ago
2. “Age of Reptiles”
3. Sierra Nevada in California and the Andes in South America
formed
4. conditions favored the survival of reptiles
5. The Triassic Period
a. dinosaurs appeared
b. dinosaurs ranged in size from squirrels to as large as 15 tons
30m long
c. ammonites, a marine invertebrate, serve as an index fossil
d. first mammals appeared
6. The Jurassic Period
a. dinosaurs where dominant life form
b. two major groups
1b. saurischians
aa. “lizard-hipped”
bb. contained herbivores and carnivores
1bb. Apatosaurs
aaa. herbivore
bbb. known as Brontosaurs
ccc. weighed 50 tons and grew 25m long
2b. ornithischians
aa. “bird-hipped”
bb. stegosaurus
1bb. 9m long and 3m tall
c. fossils of earliest birds appeared
7. the Cretaceous Period
a. dinosaurs continued to dominate Earth
b. Tyrannosaurus rex stood 6m tall and was 15m long
c. earliest flowering plants (angiosperms) appeared
1c. magnolias
2c. willows
3c. maples
4c. oaks
5c. walnuts
8. The Cretaceous-Tertiary Mass Extinction
a. the Cretaceous period ended with a mass extinction
b. dinosaur fossils have never been found in rocks formed after
Cretaceous period
c. two beliefs to the mass extinction
1c. movement of continents and increased volcanic activity
2c. impact hypothesis
aa. 65 million years ago a meteorite crashed into Earth
bb. raised enough dust to block out sun’s rays
cc. Earth’s climate became colder and plant and animal
life began to die
dd. dust formed a layer of iridium-laden rock
1dd. iridium is uncommon in rock on Earth
2dd. iridium is common in meteorites
B. The Cenozoic Era
1. started 65 million years ago and includes the present period
2. continents moved to their current position
3. the Alps and Himalayas formed by the collisions of the plates
4. known as the Age of Mammals because mammals became the
dominant life form
5. The Quaternary and Tertiary Periods
a. the two periods of the Cenozoic Era
b. Tertiary Period
1b. 65.5 million years to 1.8 million years ago
2b. includes time before the last ice age
3b. contains the Paleocene, Eocene, Oligocene, Miocene and
Pliocene Epochs
c. Quaternary Period
1c. 1.8 million years ago to present
2c. began with the last ice age and includes the present
3c. contains the Pleistocene and Holocene Epochs
6. The Paleocene and Eocene Epochs
a. many new mammals evolved
b. first primates evolved
c. worldwide temperatures dropped by about 4°C at the end of
the Eocene Epoch
7. The Oligocene and Miocene Epoch
a. the Indian subcontinent began to collide with the Eurasian
continent causing the uplifting of the Himalayas
b. climate became significantly cooler and drier
c. grasses, cone bearing trees and hardwood trees flourished
d. many early mammals became extinct
e. modern Antarctic icecap began to form
f. largest known land mammals existed
8. The Pliocene Epoch
a. predators evolved into modern forms
1a. bear
2a. dog
3a. cat
b. herbivores flourished
c. toward the end, continental ice sheets began to spread
9. The Pleistocene Epoch
a. began 1.8 million years ago
b. fossils of earliest modern humans were discovered
c. ice sheets advanced and retreated several times
10. the Holocene Epoch
a. began about 11 500 years ago and includes the present
b. ice sheets melted, sea levels rose about 140m and coastlines
took on their present shape
c. modern humans developed agriculture and began to make and
use tools made of bronze and iron