Chapter 6 Life on Earth: What Do Fossils Reveal?
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
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
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).
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.
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.
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.
Multiple-Choice Questions
1. The fossilization process involving a molecular exchange of the original substance by inorganic matter of differing composition is