Chapter 6—Life on Earth: What do Fossils Reveal?
CHAPTER 6—LIFE ON EARTH: WHAT DO FOSSILS REVEAL?
CHAPTER OVERVIEW
This chapter discusses what fossils are and how they are preserved. It also reflects some of the earliest
findings and history providing support for organic evolution by laying the foundation for paleontology, i.e.
Lamark’s theory, Darwin’s theory of natural selection, Mendelian principles of inheritance, while providing
newer views on mutations and their importance. A clear case supporting evolution is made using
paleontological evidence. The final sections of the chapter illustrate how fossils are used to correlate rock
units and establish index fossils. In addition, there is detailed discussion regarding how fossils are used to
indicate paleogeography, past climates, and give us some clues to the history of life on Earth.
LEARNING OBJECTIVES
By reading and completing information within this chapter, you should gain an understanding of the
following concepts:




Explain the processes by which fossils are preserved, i.e. permineralization, replacement
carbonization, etc.
Discuss the purpose and use of biological classification in understanding the concept of
organic evolution.
Discuss how natural selection, inheritance, and mutation can be used in explaining
organic evolution.
Discuss how fossils may be used to define and correlate paleoecological zones, and as
indicators of past environmental conditions.
CHAPTER OUTLINE
I.
Fossils: Surviving Records of Past Life
A. How Does Life of the Past Become Preserved
1. Three Common Preservation Processes
2. Molds and Casts
B. Sometimes Only Traces Remain
C. Why Are Some Fossils Rare, Yet Others Abundant
II.
Figuring Out How Life Is Organized
A. Linnaeus Leads the Way
B. What Is a Species?
C. What Is Taxonomy?
III.
Evolution: Continuous Changes in Life
A. Lamark’s Flawed Hypothesis
B. Darwin’s Theory of Natural Selection
C. Inheritance, Genes, and DNA
D. Cell Division and Reproduction: Bringing Variety to Offspring
E. Mutation: Source of Variations
F. Species, Population, and Gene Pool
G. How New Species Arise and Adaptively Radiate
H. Gradual or Sporadic Evolution
I. Phylogeny: Depicting How Ancestors Relate to Their Descendants
IV.
The Case for Evolution
A. Evidence from Paleontology
B. Evidence from Biology
V.
Fossils and Stratigraphy
A. How Do Fossils Reveal the Age of Strata?
B. The Geologic Range of Fossils: From First Appearance to Last
Chapter 6—Life on Earth: What do Fossils Reveal?
C. Using Fossils to Correlate Rock Units
D. Pitfalls of Correlating With Fossils
E. Index Fossils Especially Useful
VI.
Fossils Indicate Past Environments
A. Ecology of the Past: Paleoecology
B. The Marine Ecosystem: Diverse Habitats for Diverse Organisms
1. Pelagic Realm (Ocean Water)
2. Benthic Realm (Seafloor)
3. Benthic Life and Oozes in Deeper Water
4. Carbonate Compensation Depth
VII.
How Fossils Indicate Paleogeography
A. Paleogeographic Mapping
B. Land Bridges, Isolation, and Migration
C. Species Diversity and Geography
VIII.
How Fossils Indicate Past Climates
A. How the Oxygen-16/Oxygen-18 Isotope Ratio Indicates Ancient Seawater Temperature
IX.
An Overview of the History of Life
A. The Earliest Traces
B. The History of Plants
C. The History of Animals
D. Mass Extinctions
X.
Life on Other Planets: Are We Alone
A. Life in Our Solar System
B. Life in the Universe
Chapter 6—Life on Earth: What do Fossils Reveal?
KEY TERMS
(Pages 119–159)
abyssal marine environment (148): Environment located below 4000 meters in the oceans. There are
low temperatures, little or no light, and high pressures.
adaptation (133): A modification of an organism that better fits it for existence in its present environment
or enables it to live in a somewhat different environment.
adaptive radiation (132): The diversity that develops among species as each adapts to a different set of
environmental conditions.
Animalia (126): One of the five kingdoms in the classification system. Includes heterotrophs.
Archaea (127): The domain that includes thermophylic (heat-dependent), halophylic (salt-dependent),
methane-producing, and sulfur-producing bacteria. (The remaining two domains are the Bacteria and
Eurkarya.)
Archaebacteria (126): A member of Superkingdom Prokaryota that include the only methane producing
bacteria that are capable of living under extreme conditions of temperature or salinity are called
“extremophiles.”
assemblage zone (143): Biostratic zones which can be identified due to the occurrence of particular
fossils or genera known to exist within that certain zone.
Bacteria (domain) (127): Unicellular, prokaryotic microorganisms belonging to the Kingdom Monera.
One of the three great domains of organisms that include also the Archaea and the Eukarya.
bathyal marine environment (148): Oceanic environment encountered from the edge of the continental
shelves to a depth of about 4000 meters. It is subjected to low temperature, little or no light, and high
pressures.
benthic marine realm (145, 147): A bottom-dwelling organism.
bioturbation (147): The process of churning and mixing sediment.
biozone (142): A body of rock that is identified strictly on the basis of its contained fossils.
calcareous ooze (148): A fine-grained pelagic sediment containing undissolved sand or silt-sized
calcareous skeletal remains of small marine organisms mixed with amorphous clay-sized material.
carbonate compensation depth (CCD) (149): The water depth at which calcium carbonate is dissolved
as fast as it falls from the upper water levels.
carbonization (121): The concentration of carbon during fossilization.
cast (122): A replica of an organic object, such as a fossil shell, formed when sediment fills a mold of that
object.
chromosome (130): Genes are linked together to form larger units termed chromosomes, the central
axis of which consists of a very long DNA molecule comprising hundreds of genes.
cladogram (135): A diagram that illustrates common characteristics and relationships of different groups
of living plants or animals by their closeness of relationships to each other.
class (taxonomic) (126): A group of related orders.
concurrent range zone (143): A biostratigraphic zone recognized by the overlapping ranges of two or
more taxa (sing. taxon).
Chapter 6—Life on Earth: What do Fossils Reveal?
crossing over (genetic) (131): During initial chromosome division while chromosomes are still paired,
they may break at corresponding places and exchange their severed segments in a process called
crossing over. It results in additional mixing of genes.
deoxyribonucleic acid (DNA) (130): Chemical units or segments of a nucleic acid. The DNA molecule is
conceived as two parallel strands twisted somewhat like the handrails of a spiral staircase. The strands
are made up of phosphate and sugar compounds and are linked with cross-members composed of
specific nitrogenous bases. It indirectly controls the production of proteins, the essential components of
many basic structures and organs.
diploid cell (130): Cells having two sets of chromosomes that form pairs, as in somatic cells.
domain (126): A major taxonomic division ranking higher than a kingdom. The three domains are the
Archaea, Bacteria, and Eukarya.
ecology (143): The study of the present relationships between organisms and their environments.
ecosystem (143): Any selected part of the physical environment together with the animals and plants in
it.
epifaunal (147): Organisms living on, as distinct from in, a particular body of sediment or another
organism. They live on top of the sediment that carpets the sea floor.
Eubacteria (126): Member of Prokaryota that live in water or soil or inside larger organisms. They include
cyanobacteria.
Eukarya (domain) (126, 127): Single or multi-celled organisms that have a distinct cell nucleus and cell
membrane. Includes Animalia, Plantae, Fungi, and Protista.
extremophiles (126): See Archaebacteria.
family (taxonomic) (126): A group of related genera.
fungi (126): A kingdom of multicellular eukaryotic organisms that feed on dead or decaying organic
material.
gamete (130): Either of two cells (male or female) that must unite in sexual reproduction to initiate the
development of a new individual.
gene (130): The part of the DNA molecule that is active in the transmission of hereditary traits. The unit of
heredity transmitted in the chromosome.
gene pool (132): The sum of all genes available within a breeding population.
geologic range (e.g., of fossil species) (140): The geologic time span between the first and last
appearance of an organism.
genus (taxonomic) (125, 126): The major subdivision of a taxonomic family or subfamily of plants or
animals, usually consisting of more than one species.
hadal marine environment (148): Refers to the oceanic environment which is found at extreme depths
in oceanic trenches.
haploid cell (130): One having a single set of chromosomes, as in gametes (see diploid).
homologous structures (137): Organs having structural and developmental similarities due to genetic
relationship. Basically similar structures in superficially dissimilar organisms are referred to as
homologous.
index fossil (=guide fossil) (142): Fossil with a wide geographical distribution but narrow stratigraphic
range and thus useful in correlating strata and for age determination.
Chapter 6—Life on Earth: What do Fossils Reveal?
infaunal (147): Organisms that live and feed within bottom sediments. They burrow into soft sediment for
food and protection.
Kingdom (taxonomic) (126): A large group of related phyla.
littoral zone (147): Seaward of the supralittoral zone is the area between high and low tide known as the
littoral zone.
mass extinction (156): Marked by times of sudden worldwide extinctions of large numbers of animal and
some plant populations.
meiosis (130): That kind of nuclear division, usually involving tow successive cell divisions, that result in
daughter cells having one-half the number of chromosomes that were in the original cell.
mitosis (130): The method of cell division by which each of the two daughter nuclei receives exactly the
same complement of chromosomes as had existed in the parent nucleus. This process of cell division
produces new diploid cells with exact replicas of the chromosomal components of the parent cells.
mold (121): An impression, or imprint, of an organism or part of an organism in the enclosing sediment.
mutation (131): A stable and inheritable change in a gene.
oceanic zone (145): A division of the pelagic realm (water mass above the ocean floor), which extends
seaward from the continental shelves.
order (taxonomic) (126): A group of related families.
natural selection (128): A mechanism for evolution proposed by Charles Darwin. Competition for food,
shelter, living space, and sexual partners among species with individual variations and surplus
reproductive capacity will inevitably result in elimination of the less well fitted and survival of those that
are better fitted to their environments.
nekton (147): True swimming animals. They are able to travel where they choose under their own power.
neritic (145): A division of the pelagic realm (water mass above the ocean floor) which extends seaward
from the continental shelves.
paleoecology (143): The study of the relationship of ancient organisms to their environment.
pelagic marine realm (145): Consists of the water mass lying above the ocean floor. It is divided into the
neritic zone, which overlies the continental shelves, and the oceanic zone, which extends seaward from
the shelves.
permineralization (120): A manner of fossilization in which voids in an organic structure (such as bone)
are filled with mineral matter.
petrifaction (120): A fossilization process whereby inorganic matter dissolved in water replaces the
original organic materials, converting them to a stony substance.
phenotypic trait (126): A trait that is the observable expression of an organism’s genes.
phyletic gradualism (134): Gradual progressive change. Phyletic refers to evolutionary pathways.
Proponents believe that change occurs by slow degrees along the evolutionary pathway of a lineage.
phylogenetic tree (135): A model for depicting styles of evolution. Various taxa are traced from
outermost branches (representing lower taxonomic division such as species, genera, or families) through
a succession of junctures downward (and backward in time) to the major trunks of the higher taxa.
phylogeny (135): The historical development of groups of organisms by phylum that can be shown by a
phyogentic tree or cladogram.
Chapter 6—Life on Earth: What do Fossils Reveal?
phylum (taxonomic) (126): A group of related classes.
phytoplankton (146): Microscopic marine planktonic plants, most of which are various forms of algae.
plankton (145): Minute, free-floating aquatic organisms (includes small animals and plants that float, drift,
or feebly swim).
Plantae (126): Multicellular eukaryotes that typically live on land and make their own food by the process
of photosynthesis. They are autotrophs.
population (genetic) (132): A group of individuals that live close enough together so that each individual
has an equal chance to mate with all members of the opposite sex within the group.
Prokaryota (126): Organisms that lack membrane-bounded nuclei and other membrane-bounded
organelles.
Protista (126): A varied group of mostly unicellular organisms that, unlike the Monera, have a cell
structure that includes a nucleus and organelles. They are eukaryotes. Include heterotrophs, autotrophs,
and saprophytes.
punctuated equilibrium (134): Term suggested for evolution that consists of fitful sudden advances that
punctuate long episodes of little evolutionary progress.
range zone (142): The rock body representing the total geologic life span of a distinct group of
organisms.
replacement (121): A fossilization process in which the original skeletal substance is replaced after burial
by inorganically precipitated mineral matter.
reworked fossils (142): Fossils that have been freed from their host rock by weathering and erosion and
then reworked into younger beds. Younger strata might be mistakenly assigned to an older geologic time.
siliceous ooze (148): An ooze composed of siliceous skeletal remains of organisms, such as
radiolatians.
speciation (132): The process by which new species originate.
sublitorral zone (147): Extends from low-tide levels to the edge of the continental shelf (about 200
meters deep). Benthic animals and plants are most abundant in the continuously submerged sublittoral
zone.
supratidal zone (147): Pertaining to the shore area immediately marginal to and above the high-tide
level.
taxonomy (126): The science of naming, describing, and classifying organisms.
trace fossil (123): Tracks, trails, burrows, and other markings made in now lithified sediments by ancient
animals.
vestigial organ or structure (138): An organ that is useless, small, or degenerate but representing a
structure that was more fully developed or functional in an ancestral organism.
zooplankton (147): Planktonic animals constitute zooplankton and include protests such as radiolaria,
foraminifers, certain tiny mollusks, small crustaceans, and the motile larva of many different families of
invertebrates that live the adult stage of their life cycles on the sea floor.
Chapter 6—Life on Earth: What do Fossils Reveal?
MULTIPLE-CHOICE QUESTIONS
1.
The fossilization process involving a molecular exchange of the original substance by inorganic
matter of differing composition is
a. carbonization.
c. meiosis.
b. replacement.
d. mutation.
2.
An inheritable change in genetic material within cells is called
a. mutation.
c. meiosis.
b. mitosis.
d. diploid cells.
3.
Gradual progressive change is referred to as
a. punctuated equilibrium.
c. mutation.
b. peripheral isolation.
d. phyletic gradualism.
4.
Which taxonomy list—from largest to smallest—is correct?
a. order, species, family, genus, phylum, kingdom, class
b. species, genus, family, order, class, phylum, kingdom
c. kingdom, phylum, class, order, family, genus, species
d. species, order, genus, phylum, class, family, kingdom
5.
Organs that were utilized in earlier ancestral forms but whose importance has diminished with
changes in environment and habits are called
a. variable structures.
c. homologous.
b. mutations.
d. vestigial.
6.
The structures that are the result of variations and adaptations to particular environmental
conditions, but similarities indicate possible ancestry are called
a. variable structures.
c. adaptive positive structures.
b. vestigial structures.
d. homologous structures.
7.
Evolution that consists of fitful sudden advances after long episodes of little evolutionary progress is
termed
a. mutation.
c. adaptive radiation.
b. punctuated equilibrium.
d. adaptation.
8.
Darwin’s study of finches in the Galapagos determined that species of related ancestry evolved
differently because they adapted to different environments illustrates the concept of
a. convergent evolution.
c. phyletic gradualism.
b. parallel evolution.
d. adaptive radiation.
9.
The largest number of benthic (bottom dwelling) animals and plants live in the continuously
submerged zone known as
a. bathyal.
c. littoral.
b. sublittoral.
d. abyssal.
10.
The “supratidal zone” of the bottom (benthic) realm of the marine ecosystem is located
a. below the abyssal zone.
c. in a narrow zone above high tide.
b. at the deepest depths of the ocean floor. d. below the sublittoral zone.
11.
A type of zone that is recognized by the overlapping ranges of two or more taxa is called
a. concurrent range zone.
c. range zone.
b. assemblage zone.
d. endemic range.
12.
Fossils that are abundant, widely dispersed and derived from organisms that lived during a
relatively short span of geologic time are
a. reworked fossils.
c. haploid.
b. guide fossils.
d. trace fossils.
Chapter 6—Life on Earth: What do Fossils Reveal?
13.
The interval between the first and last appearance of a species constitutes the
a. geologic time.
c. geologic range.
b. rate of evolution.
d. relative geologic age.
14.
An animal or plant that is confined to a particular environmental area is said to be
a. species specific.
c. endemic.
b. vagile.
d. pelagic.
15.
Paleoecologists have two divisions of classification for oceanic environment. They are
a. phytoplankton and nekton.
c. littoral zone and sublittoral zone.
b. pelagic realm and benthic realm.
d. neritic zone and oceanic zone.
16.
The pelagic realm which consists of the water mass lying above the ocean floor can be further
divided into
a. nectonic zone and abyssal zone.
c. neritic zone and oceanic zone.
b. nectonic zone and hadal zone.
d. supralittoral zone and littoral zone.
17.
What is the process of cell division that produces new diploid cells with exact replicas of the
chromosomal components of the parent cells?
a. meiosis
c. mutation
b. fertilization
d. mitosis
18.
The realm of water mass lying immediately above the sea floor is known as the
a. oceanic realm.
c. pelagic realm.
b. supralittoral realm.
d. benthic realm.
19.
Which of the following is not a positive trait of an Index (Guide) fossil?
a. abundant
c. short geologic range
b. widely dispersed
d. long geologic range
20.
The benthic realm includes the following zones with the exception of this realm.
a. sublittoral zone
c. littoral zone
b. supratidal zone
d. neritic zone
Chapter 6—Life on Earth: What do Fossils Reveal?
FILL IN THE BLANK
1.
The type of fossilization that occurs when soft tissues are preserved as thin films of
carbon is ___________________
.
2.
The part of the DNA molecule that is active in the transmission of hereditary traits
is called _
.
3.
Organs that have the same pattern of embryological development, but different functions
are called ___________________.
4. During the initial chromosome division while chromosomes are still paired, they
may break at corresponding places and exchange their segments in a process
called
.
5.
A biostratigraphic zone recognized by the overlapping ranges of two or more taxa is
called _____________________________________
.
6.
The type of phylogeny used to describe organisms that are analyzed objectively on
the basis of characteristics they share in order to determine their ancestordescendant relationship is called
.
7.
Fossils used for age determination with a wide geographical distribution but narrow stratigraphic
range and thus useful in correlating strata are called
8.
9
Populations whose members can interbreed when they come into contact are grouped into that
larger biologic unit called a
.
The diversity that develops among species as each adapts to a different set of environmental
conditions is called
.
10.
The single most important contribution to the concept of organic evolution made by Charles Darwin
was his proposal of
.
11.
____________________________ means “to spread minerals throughout.”
12.
Clues to a creature’s appearance and how it lived can be obtained by examining ___________
__________ which are tracks, burrow, borings, and trails.
13.
A group of species that have close ancestral relationships is called a ______________.
14.
Structures that are basically useless and usually size-reduced in one species but useful and well
developed in a related species are called ________________ ________________.
15.
___________________ studies how ancient organisms interacted with one another and their
environments.
.
Chapter 6—Life on Earth: What do Fossils Reveal?
TRUE/FALSE
1.
In biologic classification, an order is lower in rank than in class, but higher than a family.
2.
Replacement is a process that involves a simultaneous exchange of the original substance of
part of a dead plant or animal with mineral matter of a different composition.
3.
In biological and paleontological classification, the basis for classifying organisms is shared
characteristics.
4.
Diploid cells result from the process of meiosis.
5.
A gene pool is represented by the individuals within a population that has its own particular
combination of genes.
6.
Cells with paired homologous chromosomes are called haploid cells.
7.
The benthic zone of the ocean ecosystem consists of the water mass lying above the ocean
floor.
8.
Vestigal structures have the same pattern of embryological development, but different
functions.
9.
Phylogeny refers to the historical development of groups of organisms. Phylogeny can be
depicted on a tree or bush like a diagram or as a cladogram.
10.
The five major episodes of mass extinction would include the end of the Ordovician, late
Devonion, late Silurian, end of the Permion, end of the Cretaceous.
Chapter 6—Life on Earth: What do Fossils Reveal?
ANSWER KEY
Multiple Choice
1. b
2. a
3. d
4. c
5. d
6. d
7. b
8. d
9. b
10. c
11. a
12. b
13. c
14. c
15. b
16. c
17. d
18. c
19. d
20. d
Fill Ins
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
carbonization
gene
homologous
crossing over
concurrent range zone
cladistic
guide fossils
species
adaptive radiation
natural selection
Permineralization
trace fossils
genus
vestigal organs
Paleoecology
True/False
1. T
2. T
3. T
4. F
5. T
6. F
7. F
8. F
9. T
10. F
Chapter 6—Life on Earth: What do Fossils Reveal?
RESPONSES TO QUESTIONS ACCOMPANYING
SELECTED FIGURES
FIGURE 6–3 (p. 121) Minerals other than pyrite that occur in fossil replacements are calcite,
dolomite, quartz, and hematite.
FIGURE 6–9 (p. 124) In the oxygen-deficient peat bog, there would be little free oxygen available
to combine with carbon in the soft tissue to cause loss of carbon as carbon dioxide. Hence, this
type of decay is minimized.
FIGURE 6–10 (p. 124) Because original grain orientation would have been destroyed by
burrowing worms, this rock would not be suitable for determining the current direction of the
depositing medium.
FIGURE 6–11 (p. 125) Because the tracks of the quadruped (Stegosaurus) cover those of the
biped (Allosaurus) near the center of the figure, the quadruped crossed the area at some time
after the biped did.
FIGURE 6–12 (p. 125) Both C and E would serve as “way up” or geopetal indicators. The 180°
loop or the tapered point of C indicates the downward direction, as do the downwardly directed
branches of the burrows in E.
FIGURE 6–24 (p. 135) Requires a sketch.
FIGURE 6–27 (p. 138) Overlapping arrangement of ulna and radius permits 180 degrees rotation
of the forearm.
FIGURE 6–37 (p. 134) If photosynthesis proceeds unchecked with sufficient sunlight no
component on this cycle will be depleted.
FIGURE 6–38 (p. 146) Pseudopodia in this planktonic foraminifer were used to catch food and
provided buoyancy.
FIGURE 6–39 (p. 147) Requires an arrow on each of the representative groups.
FIGURE 6–41 (p. 148) Diatoms are members of the kingdom Protoctista.
FIGURE 6–49 (p. 150) The boundaries of regions of erosion would be drawn around areas where
no rocks of Carboniferous age exist. Carboniferous rocks along the periphery of this margin
should exhibit abrupt truncation. Bedrock in the areas of no Carboniferous should be preCarboniferous age.