1. “A Trip Through Geologic Time”
CHAPTER 20
“A Trip Through Geologic Time”

2. p. 613: 1. What are the 4 eras of geologic time?
Precambrian, Paleozoic, Mesozoic, and Cenozoic

3. 2. How is a geologic period different from an era?
An era is the longest division of geologic time. It is broken down in to smaller divisions called periods.
Much like a year is broken down into small divisions called months….and months are broken down into small divisions called days….

4. 3. What occurred on Earth 4.6 billion years ago?
(This is the beginning of Earth as we know it).
Earth was a planet of very hot, molten rock with many volcanic eruptions. The atmosphere consisted mainly of poisonous gases. This was the beginning of the Precambrian era.

5. 4. Look at figure What seems to be the major trend in development of life forms during geologic time?
The life forms develop from very simple (jellyfish, corals, clams) to more complex (wooly mammoths…man)

6. Section 20-1: “The Geologic Time Scale”
Scientists have established the geologic time scale to divide geologic time into
workable units.
2. Earth’s history is divided into 4 geologic eras: PRECAMBRIAN ERA, PALEOZOIC ERA, MESOZOIC ERA and CENOZOIC ERA.

7. Divisions An ERA is the LARGEST division of the geologic time scale.
Eras are broken into small subdivisions called PERIODS.
Eras are of DIFFERENT lengths.
Pre-cambrian Era
Paleozoic
Era
Mesozoic
Cenozoic

8. Early Earth History “Precambrian Era”
The LONGEST era lasting about 4 billion years.
Accounts for about 87% of Earth’s history.
“The DAWN OF LIFE”
Rocky shorelines with no life on land
Climate:
Fiery and HOSTILE climate.
POISONOUS gases in the atmosphere.

9. Precambrian (continued)
Life:
Found only in the SEAS AND TIDEPOOLS
Earliest living organisms are: BACTERIA and BLUE-GREEN ALGAE
First fossils ever found were of BACTERIA
First animal life found at the end of this era: Invertebrates like JELLYFISH and WORMS, SPONGES and CORALS

10. Precambrian Land Land: IGNEOUS rocks
Mountain building – granite mountain ranges
“SHIELDS” are the oldest rocks on earth
Half of our mineral deposits are found near these mountain ranges: IRON, COPPER, NICKEL, GOLD AND SILVER.

11. Paleozoic Era
Life: Creatures of the Paleozoic seas: SHELLS, starfish, FISH, brachiopods, and TRILOBITES.
1st vertebrate is the FISH
Fossils found (exoskeletons, vertebrates)
Life comes ashore – Life on land:
Huge forests of ferns and sago palm
CYCADS are among the first seed plants.
These forests formed the huge COAL deposits in the United States
IMPORTANT INDEX FOSSIL: TRILOBITE

12. Paleozoic Era “Life continues”
1.AMPHIBIANS the first land vertebrates. Means “ living a DOUBLE-LIFE spending early lives in water and then moves to land
Example: is the Eryop
REPTILES with tough skin, scales, leather eggs and hard plates develop.
Alligators, wasps, beetles exist

13. Paleozoic Land Climate:
Warm and HUMID at the beginning of the era; flooding often.
Climate cools later
Land:
Mountains rising in parts of North America (Appalachian mountains), Norway, Scotland and Greenland

14. 20-3: Middle and Recent Earth History
Mesozoic divided into 3 PERIODS.
1. TRIASSIC
2. JURASSIC
3. CRETACEOUS
This era is a period of many CHANGES both in the land and in the living things that inhabit the earth.

15. Mesozoic Era PANGAEA broke apart
Numerous earthquakes and VOLCANIC eruptions throughout this era.
Many mountains formed at this time:
Sierra Nevada, and the Rocky Mountains

16. Triassic Period
Life:
Large reptiles that have lungs and breathe air have returned to the SEAS
MAMMALS appear: have fur, offspring do not hatch from eggs; young grow and mature in mom’s body before birth
Ferns and seeds still common. Cycads are now BIGGER.
Very first small DINOSAURS (no bigger than chickens) appear

17. Triassic Period Land and Climate
North and South America begin to SEPARATE FROM AFRICA
Narrow sea opens between North America,
and Europe known as the ATLANTIC OCEAN
Southern lands still joined: Africa, South America, Antarctica and India
Climate:
DROUGHT exists
Hotter than ever before

18. Jurassic Period Life: “Age of the DINOSAURS”
Huge CYCADS and modern-looking evergreens called CONIFERS make up the forests
First BIRD - Archaeopteryx
Climate:
Dry and WARM
Land:
“Supercontinent” Animals and plants are similar
VOLCANOES active in the American West

19. Cretaceous Period Time of rapid “ ______________” Life:
Dinosaurs __________(Tyrannosaurus, Triceratops)
Herbivores and ____________
Only crocodiles, turtles, lizards and ________ survived from earlier periods.
__________ plants appeared (magnolia, oak, fig, poplar, and elm)
Most of the great tree ferns and cycads ______________
Mass _________________ occurred at end of period

20. Cretaceous Land and Climate
Time of widespread FLOODING.
Continents continue to spread APART
North America and Europe are still joined
At end of period – sea levels dropped;
rivers and flood plains dried up.
Climate: Why was there a mass extinction of life?
Drastic change:
CLIMATE change
Disease
Gigantic ASTEROID crashed into Earth

21. Cenozoic Era This is the era in which we live today
Divided into 2 periods (Tertiary and Quaternary)
Tertiary Life:
Grassy meadows; groups of REDWOODS, oaks and cedar trees.
Birds singing; “Unita beasts” (ancient rhino)
First HUMAN LIKE creatures begin walking upright on the African plains. “Lucy” – 1 meter tall
Climate:
Mild climate throughout this period
Land:
Himalaya Mountains rise; Grand canyon formed

22. Quarternary Period Climate: Sharply colder; ICE Age
Great sheets of ice from Arctic and Antarctic advance and cover one-FOURTH of the land on earth
Last ice age ended 11,0000 years ago
World warms; FARMING becomes widespread and modern civilization begins
Life:
First modern HUMAN BEINGS APPEAR, wooly mammoths die out