CHAPTER 9 A VIEW OF EARTH’S PAST
II. PRECAMBRIAN TIME AND THE PALEOZOIC ERA
A. Evolution
1. fossils indicate the kinds of organisms that lived when rock formed
2. scientists have discovered evidence that species of living things have
changed over time
3. evolution – a heritable change in the characteristics within a
population from one generation to the next; the development of new
types of organisms from preexisting types of organisms over time
4. the theory of evolution by natural selection was proposed in 1859 by
Charles Darwin
5. Evolution of the Geologic Column
a. major geologic and climatic changed can affect the ability of
some organisms to survive
b. scientists try to determine how environmental changes affected
organisms in the past
1b. dramatic changes in sea level
2b. temperature changes
c. fossil records show some organisms survived while others
became extinct during environmental changes
d. study of fossils show why some survived and others became
extinct
B. Precambrian Time
1. Earth formed about 4.6 billion years ago
2. a large cloud (nebula) spun around until particles clumped together
to form Earth
3. formation of Earth took from 4.6 billion years ago to 542 million
years ago (approximately 4 billion years)
4. makes up 88% of Earth’s history
5. little is known about Precambrian time
6. Precambrian rocks
a. shields
1a. large areas of exposed Precambrian rocks
2a. exist on every continent
b. a result of several hundred million years of volcanic activity,
mountain building, sedimentation and metamorphism
c. nearly half of the valuable mineral deposits in the world occur
in rocks of Precambrian time
1c. nickel
2c. iron
3c. gold
4c. copper
7. Precambrian life
a. fossils are rare of Precambrian life forms
1a. no bones
2a. no shells
3a. no hard parts
4a. volcanic activity, erosion, crustal movements,
metamorphism
b. stromatolites
1b. reef-like deposits formed by blue-green algae
2b. form today in warm shallow water
3b. supports the idea that Precambrian rocks were covered
by water
c. imprints of marine worms, jellyfish and single-celled organisms
have been discovered in Precambrian rocks
C. The Paleozoic Era
1. 542 million years to 251 million years ago
2. beginning of Era, landmasses scattered
3. Pangaea (single landmass) formed at the end of the era
4. extensive fossil record
5. Divided into seven periods
a. The Cambrian Period
1a. first period
2a. warm shallow seas covered much of the Earth
3a. marine invertebrates thrived in the warm water
4a. trilobites are used as index fossils for this period
5a. brachiopods were the second most common invertebrate
6a. no plant life on land
b. The Ordovician Period
1b. population of trilobites began to shrink
2b. invertebrate graptolites flourished
3b. vertebrate animals began to appear
4b. no plant life on land
c. The Silurian Period
1c. vertebrate and invertebrate life forms flourished
2c. eurypterids existed (Fig. 6, Page 219)
3c. earliest land plants and scorpions evolved on land
d. The Devonian Period
1d. “Age of Fishes”
2d. first amphibians began to appear
3d. giant horsetails, ferns and seed bearing plants began to
develop
4d. brachiopods and mollusks continued to thrive
e. The Carboniferous Period
1e. Mississippian and Pennsylvanian Period
2e. very warm and extremely high humidity
3e. means “carbon bearing”
4e. large coal deposits of today are from this period
5e. vertebrates adapted to life on land resembling large
lizards
f. The Permian Period
1f. end of the Paleozoic Era
2f. a mass extinction occurred at the end of the Permian
Period
3f. Pangaea formed
4f. many species of marine invertebrates disappeared due to
retreating, shallow inland seas