CHAPTER 20

“A Trip Through Geologic Time”

p. 613: 1. What are the 4 eras of geologic time?

Precambrian, Paleozoic, Mesozoic, and Cenozoic

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….

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.

4. Look at figure 20-3. 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)

Section 20-1: “The Geologic Time Scale”

1. 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.

Divisions

1. An ERA is the LARGEST division of the geologic time scale.

2. Eras are broken into small subdivisions called PERIODS.

3. Eras are of DIFFERENT lengths.

Pre-cambrian

Era

Paleozoic

Era

Mesozoic

Era

Cenozoic

Era

Early Earth History“Precambrian Era”

1. The LONGEST era lasting about 4 billion years.

2. Accounts for about 87% of Earth’s history.3. “The DAWN OF LIFE” 4. Rocky shorelines with no life on landClimate:Fiery and HOSTILE climate.POISONOUS gases in the atmosphere.

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

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.

Paleozoic Era

Life: Creatures of the Paleozoic seas: SHELLS, starfish, FISH, brachiopods, and TRILOBITES.

1st vertebrate is the FISHFossils 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 StatesIMPORTANT INDEX FOSSIL: TRILOBITE

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

2. REPTILES with tough skin, scales, leather eggs and hard plates develop.

3. Alligators, wasps, beetles exist

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

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.

Mesozoic Era

1. PANGAEA broke apart

2. Numerous earthquakes and VOLCANIC eruptions throughout this era.

3. Many mountains formed at this time:

Sierra Nevada, and the Rocky Mountains

Triassic Period

Life: Large reptiles that have lungs and breathe air have

returned to the SEASMAMMALS 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

Triassic Period Land and Climate

Land: 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 IndiaClimate: DROUGHT exists Hotter than ever before

Jurassic Period

Life: “Age of the DINOSAURS” Huge CYCADS and modern-looking evergreens

called CONIFERS make up the forests First BIRD - ArchaeopteryxClimate: Dry and WARMLand: “Supercontinent” Animals and plants are similar VOLCANOES active in the American West

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

Cretaceous Land and Climate

Land: 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

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 tallClimate: Mild climate throughout this periodLand: Himalaya Mountains rise; Grand canyon formed

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 beginsLife: First modern HUMAN BEINGS APPEAR, wooly mammoths die

out