CHAPTER 9 A VIEW OF EARTH’S PAST
I. GEOLOGIC TIME
- geologic time scale – a scale that outlines the development of Earth and of life on Earth
A. Geologic Column
1. 19th century scientists determined the relative ages of sedimentary rock in different areas around the world
a. studying fossils
b. applying Law of Superposition
2. no single area on Earth contained a record of all geologic time
3. scientists developed the geologic column
a. an ordered arrangement of rock layers that is based on the relative ages of the rocks and in which the oldest rocks are at bottom
b. rock layers are distinguished by the types of rocks
c. rock layers are distinguished by the kinds of fossils located
1c. fossils in the upper rock layers resemble modern plants and animals
2c. fossils in lower rock layers are of plants and animals that are different from those living today
3c. many fossils discovered in old layers are from species that are extinct
4. Using a Geologic Column
a. first columns developed estimated age or rocks by rate of deposition
b. radiometric dating allowed scientists to determine absolute age more accurately
c. scientists use more geologic columns to determine absolute age without radiometric dating by using index fossils
B. Divisions of Geologic Time
1. the geologic history of Earth is marked by major changes
a. Earth’s surface features
b. climate changes
c. types of organisms
2. geologists use the above indicators to divide the geologic time scale into smaller units
3. units of geologic time is generally characterized by fossils of a dominant life form (Table 1, page 213)
4. the abbreviation “Ma” stands for mega-annum
a. means “one million years”
b. used to better discuss geologic time
5. Eons and Eras
a. eon is the largest unit of geologic time
b. geologic time is divided into four eons
1b. Hadean Eon
2b. Archean Eon
3b. Proterozoic Eon
4b. Phanerozoic Eon
c. Precambrian Time
1c. contains the first three eons
2c. four billion years
3c. very few fossils (why?)
aa. organisms were very primitive
bb. much of the rock from that time is either igneous or metamorphic
d. eras
1d. a unit of geologic time that includes two or more periods
2d. smaller than an eon
3d. Phanerozoic Eon
aa. Paleozoic Era
1aa. first era of Phanerozoic Eon
2aa. lasted 291 million years
3aa. fossils were a wide variety of marine and terrestrial life forms
bb. Mesozoic Era
1bb. lasted 186 million years
2bb. fossils include early forms of birds and reptiles
cc. Cenozoic Era
1cc. present age
2cc. began 65 million years ago
3cc. fossils of mammals are common
6. Periods and Epochs
a. period
1a. a unit of geologic time that is longer than an epoch but shorter than an era
2a. characterized by specific fossils
3a. usually named for the location in which the fossils were first discovered
b. epoch
1b. a subdivision of time that is longer than an age but shorter than a period
2b. created by certain criteria
aa. rock record is most complete
bb. rock record is least deformed
cc. detailed fossil record
3b. ages
aa. subdivision of epoch
bb. defined by the occurrence of distinct fossils
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
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 and 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