The Earth Through Time
Chapter 6—Life on Earth: What Do Fossils Reveal?
CHAPTER OUTLINE FOR TEACHING
I. Modes of Preservation
A. Permineralization
B. Replacement
C. Carbonization
D. Molds and Casts
E. Soft Tissue Preservation (for example, in amber)
F. Trace Fossils
1. Tracks and trails
2. Burrows
3. Borings
II. Nature of Fossil Record
A. Hard versus Soft Parts
B. Rapid versus Slow Burial (Favorable and Unfavorable Places)
III. Rank and Order (Linnaean taxonomy, c. 1750)
A. Concept of a species as fundamental unit
1. Biologic concept
2. Paleontologic concept
B. Taxonomic Order (Hierarchy)
1. Kingdom
2. Phylum
3. Class
4. Order
5. Family
6. Genus
7. Species
C. Taxonomy of the Three Domains
1. Domain Archaea – methane-producing bacteria and bacteria capable of living in extreme conditions
2. Domain Bacteria – cyanobacteria and many other prokaryotes
3. Domain Eukarya
a. Kingdom Protista (mostly single-celled organisms)
(1) heterotrophs – food devourers
(2) autotrophs – photosynthesizers
(3) saphrophytes – decomposers
b. Kingdom Fungi (multicellular eukaryotes, many of which are saprophytes)
c. Kingdom Plantae (autotrophic multicellular eukaryotes)
d. Kingdom Animalia (heterotrophic multicellular organisms)
IV. Organic Evolution
A. Lamarck’s Theory (c. 1815)
1. All species descended from others
2. New structures appear out of “need” or “want”
3. Once acquired, structures can be passed on
B. Darwin’s Mechanism of Natural Selection (1859)
1. Cause of variation was not known
2. Variations in a population are common
3. Favorable ariations in population allow survival
C. Mendelian Principles of Inheritance (1865)
1. Cause of variation was not known
2. Variation documented experimentally
D. Modern Genetics
1. Genes are determiners
2. DNA molecule active in hereditary transmission
3. Genes as part of DNA
4. Chromosomes as links within DNA
E. Cell Division and Reproduction
1. Chromosomes kind and numbers are constant for a species
2. Diploid cells – cells with paired homologous chromosomes
3. Mitosis – regeneration of new cells in organisms
4. Meiosis – occurs in sexual reproduction when gametes are formed
5. Haploid cells – reproductive cells without paired chromosomes
6. Variation in offspring
a. mixing parental chromosomes
b. crossing over (exchange of severed segments during chromosome division)
F. Mutation as the Source of Variation
1. Mutation can occur spontaneously (without specific cause)
2. Mutation via UV-light, cosmic rays, gamma-rays, chemicals
3. Sex cell mutation strongly affects evolution
G. Modern Organic Evolution
1. Change due to: mutation, natural selection
2. Concept of population
3. Concept of gene pool
4. Speciation is origin of species
5. Concept of reproductive or geographic barriers
6. Adaptive radiation
7. Gradual versus punctuated equilibrium
a. phyletic gradualism
b. punctuated equilibrium
8. Phylogeny and phylogenetic trees
a. phylogenetic tree
b. cladogram
9. Evidence of evolution
a. paleontologic
b. biologic (homologous structures, vestigial organs)
c. DNA sequences
V. Fossils and Stratigraphy: establishing age equivalence of strata using fossils
A. Key Findings
1. Principle of fossil succession
2. Life has changed through time
3. Principle of superposition
4. Extinction: permanent loss of a species
5. Similar fossils in similar environments of same age
B. Correlation by Fossils
1. Key fossils – correlative value based on geologic range
a. first occurrence (oldest)
b. last occurrence (youngest)
2. Assemblages of fossils – also have correlative value
3. Index (guide) fossils – abundant, widely dispersed, lived short time
4. Reworked fossils – fossils from a older interval
5. Biostratigraphic zones (biozones)
a. range zone
b. concurrent range zone
c. assemblage zone
VI. Ancient Environments and Fossils (Paleoecology)
A. Marine Realms
1. Pelagic (Neritic and Oceanic)
a. floaters (plankton and phytoplankton)
b. swimmers (nekton – such as crustaceans, cephalopods, and vertebrates)
2. Benthic: supratidal, littoral, sublittoral, bathyal, abyssal, hadal
a. bioturbation – animal-sediment interaction on seafloor
b. oozes – siliceous and calcareous bioclastic material on seafloor
c. carbonate compensation depth – depth at which carbonate dissolves on seafloor (about 4-5 km)
B. Environmental Reconstruction (Paleogeography)
1. Land bridges, isolation, and migration
2. Species diversity and geography
3. Biofacies analysis
C. Ancient Climatic Reconstruction (Paleoclimatology)
1. Distribution of key plants and animals
2. Oxygen-16/Oxygen-18 isotopic ratios
VII. Overview of History of Life
A. Precambrian
1. First one billion years — no fossil record
2. More than 3.5 billion to 700 million years ago—bacteria, algae, cyannobacteria (stromatolites)
3. 700 million years ago—fossil metazoans (worms, arthropods, and relatives of the corals and jellyfish) first appear
B. Phanerozoic
1. Evolution of plants
a. Late Ordovician – land plants appeared
b. Earliest Cretaceous – flowering plants appeared
2. Evolution of animals
a. Paleozoic: marine invertebrates, first vertebrates
b. Mesozoic: more marine invertebrates, land vertebrates
c. Cenozoic: more marine invertebrates and vertebrates; modern mammals
C. Mass Extinctions
1. End of Ordovician
2. Late Devonian
3. End of Permian
4. Late Triassic
5. End of Cretaceous
VIII. Life on Other Planets
A. Life as We Know It: places to look
1. Mars
2. Jupiter’s satellites (Europa and Io)
3. Saturn’s satellite (Titan)
B. Life on other planets: there may be as many as 1000 or more planets in the numerous other solar systems of the universe where there may be life as we define it.
Answers to Discussion Questions
1. Factors in determining whether a fossil will be valuable and not as an indicator of age and for correlation include: cosmopolitan distribution of the fossil, good preservation, and having a relatively short span of existence.
2. a) Ordovician through Permian. b) Ordovician. c) Fossil A has the narrower age range, and is therefore the better guide fossil.
3. The different, coeval fossil assemblages can be accounted for by different, coeval environments and fossil assemblages of organisms sensitive to those environmental differences.
4. These older fossils (conodonts) may have been reworked by erosion of a Devonian unit, thus contributing fossil—containing detrital to the Permian unit.
5. During Paleozoic, vascular land plants such as psilopsida, lycopsida (scale trees), sphenopsida, pteropsida (tree ferns), pteridospermophyta (seed ferns), ginkophyta (ginkgoes), and coniferophyta (conifers) existed on land. This list includes all main groups of vascular land plants except angiosperms and cycads and cycadeoids.
6. a) Mitosis is the reproduction of exact copies of cells as in asexual reproduction and production of somatic cells in sexually reproducing organisms. Meiosis is reproduction unicellular or sexually reproducing multi-cellular organisms where in two divisions produce four haploid (daughter) cells without paired chromosomes. The haploid cells are sexual gametes which fuse during sexual reproduction. b) Cells without paired chromosomes are haploid; cells with paired homologous chromosomes are diploid. c) Gymnosperms are non-flowering plants that produce pollen or seeds; angiosperms are flowering plants that produce pollen or seeds. d) Cladograms like phylogentic trees show relationships between organisms, but the cladogram is completely objective and ignores the age relationships among organisms involved.
7. Adaptation is acquisition of heritable characteristics that are advantageous to an individual and a population. The honey creepers of Hawaii, displaying various adaptations of beak sizes and shapes, are a good example.
8. The theory of biologic evolution has been supported by the fossil succession record and extinction evidence. The paleontologic evidence is at least as important to reconstruction of past geographies as physical (sedimentologic evidence). The paleontologic evidence can be a detailed record of past climate change as in isotopic shell studies and coiling patterns of foraminifers, for example. Paleontologic evidence helps reconstruct ancient environments by using fossils as clues (e.g., the mode of life of a trace or body fossil suggests characteristics of ancient environments).
9. Darwin established natural selection as the driving force in macroevolution. Mendel discovered the fact that unknown but heritable factors (genes) were the cause of the variation Darwin observed.
10. The ranges of fossils are carefully documented in global correlation that has been studied for many decades.
11. Phyletic gradualism and punctuated equilibrium are opposite in that the former stresses slow, gradual change and the latter abrupt change, then stasis. A continuous core from the ocean would intuitively yield better samples for study of gradual versus punctuated events.
12. The sublittoral zone is continuously covered by sea water, but is shallow enough for light to penetrate readily to the seafloor. Light promotes the growth of algae and other marine plants, which are important parts of the food chain. Soft, oxygenated bottom sediments are good habitats for marine organisms that engage in bioturbation.
13. Heterotropic means that the organism has to consume something to make energy and it does not make energy from the Sun. Prokaryotic means that the cell lacks a nucleus. And, anerobic means that it does not require oxygen to survive.
14. e 15. b
CHAPTER ACTIVITIES
Student activities for in-depth learning:
1. There are many different types of trace fossils and these are made by various organisms interacting with the sediment during the time they lived. Take a look at the various types of trace fossils and make a list of all of them by looking that the Nova Scotia Museum page at http://museum.gov.ns.ca/mnh/nature/tracefossils/english/. Visit the “Whodunnit” section of this page and make a sketch of three different trace fossils and explain how the organism in question made each trace fossil.
2. Using your computer’s search engine, conduct a search for “stromatolites.” Take a look at images of both modern and ancient stromatolites. How and where do stromatolites form today and how and where did they form in the distant past? Just how far back in the geological record do we find stromatolites? Based on the field photographs you find on the web showing stromatolites, how would you recognize one yourself? Why do you suppose stromatolites have been alive so long on Earth? Use web resources and your textbook for answers.
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, for example, 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
The Case for Evolution
J. Evidence from Paleontology
K. Evidence from Biology
IV. 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
V. 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
VI. How Fossils Indicate Paleogeography
A. Paleogeographic Mapping
B. Land Bridges, Isolation, and Migration
C. Species Diversity and Geography
VII. How Fossils Indicate Past Climates
A. How the Oxygen-16/Oxygen-18 Isotope Ratio Indicates Ancient Seawater Temperature
VIII. An Overview of the History of Life
A. The Earliest Traces
B. The History of Plants
C. The History of Animals
D. Mass Extinctions
IX. Life on Other Planets: Are We Alone?
A. Life in Our Solar System
B. Life in the Universe
Key Terms (pages given in parentheses)
abyssal marine environment (153): Environment located below 4000 meters in the oceans. There are low temperatures, little or no light, and high pressures.
adaptation (137): 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 (137): The diversity that develops among species as each adapts to a different set of environmental conditions.
Animalia (132): One of the five kingdoms in the classification system. Includes heterotrophs.
Archaea (domain) (132): The domain of life that includes microscopic life that thrives in extreme enviroments
assemblage zone (150): Biostratigraphic zones which can be identified due to the occurrence of particular fossils or genera known to exist within that certain zone.
Bacteria (domain) (133): Unicellular, prokaryotic microorganisms belonging to the Kingdom Monera. One of the three great domains of organisms that include also the domains Archaea and Eukarya.