FAQs about Geology

FAQs about Geology

What is science?

Science refers to the various processes through which knowledge is gained through reproducible observation or experimentation. An observation that is not reproducible is not a scientific observation. In the context of geology, we seek knowledge of the natural world, both now and throughout its history.

Science is a data-driven enterprise. In the absence of reproducibly obtained data, there is no science. We do not develop scientific hypotheses simply through deductive reasoning from supposed "first principles," in the manner that some ancient Greek philosophers sought to understand the world. Rather, we reproducibly collect data, and those data define and constrain our ideas of how the natural world actually works.

Quantitative scientific observations are always reported with an associated error estimate, either explicitly by stating a confidence interval or implicitly through an appropriate choice of significant figures. For example, the age of a volcanic ash bed might be reported to a 95% confidence interval as 138.4 +/- 0.2 million years, which means that we would expect that the average of a very large number of duplicate analyses of that ash to fall between 138.2 and 138.6 million years. Formal statistical procedures exist for obtaining reliable error estimates, and for choosing the appropriate number of significant figures.

The reproducible observations constitute the "facts" that are related to one another through the development of hypotheses and models. Relationships among the primary data are generally expressed mathematically. The defining characteristic of a scientific hypothesis is that it must be testable or falsifiable using reproducible observations. An idea that cannot be tested is not a scientific hypothesis.

Scientific hypotheses are developed to fit data; data are not collected to fit or support hypotheses post facto. Rather, data are collected to test or disprove hypotheses.

References and suggested reading:

  • Ben-Ari, Moti, 2005, Just a theory -- exploring the nature of science: Amherst, New York, Prometheus Books, 237 p., ISBN 1-59102-285-1.
  • Bridgman, P.W., 1927, The logic of modern physics: New York, Arno Press [reprinted 1980], 228 p., ISBN 0-405-12594-1.
  • Bronowski, J., 1965, Science and human values: New York, Harper and Row, 119 p., ISBN 0-06-097281-5.
  • Bronowski, J., 1978, The common sense of science: Cambridge, Massachusetts, Harvard University Press, 154 p., ISBN 0-674-14651-4.
  • Lee, J.A., 2000, The scientific endeavor -- a primer on scientific principles and practice: San Francisco, California, Benjamin Cummings, 186 p., ISBN 0-8053-4596-5.
  • Morrison, P., and Morrison, P., 1987, The ring of truth -- an inquiry into how we know what we know: New York, Random House, 307 p., ISBN 0-394-55663-1.
  • Scott, E.C., 2004, Evolution vs. creationism -- an introduction: Berkeley, University of California Press, 272 p., ISBN 0-520-24650-0. Chapter 1, Science: "truth without certainty," is particularly relevant.
  • Snow, C.P., 1959, The two cultures: Cambridge, UK, Cambridge University Press, 107 p., ISBN 0-521-45730-0 (Canto edition, 1993).
  • Wolpert, L., 1992, The unnatural nature of science -- why science does not make (common) sense: Cambridge, Massachusetts, Harvard University Press, 191 p., ISBN 0-674-92980-2.

What is geology?

Geology is a very broad area of the natural sciences that is primarily concerned with the materials, physical/chemical processes, and developmental history of the Earth and its major systems: biosphere, atmosphere, hydrosphere, lithosphere, and deep interior. Through the fields of planetary and space science, geology includes the rest of the Solar System and beyond within its sphere of interest.

Geology is an integrative field of science that utilizes or overlaps with other primary fields of quantitative inquiry such as physics, chemistry, biology, mathematics, atmospheric sciences, and engineering (materials science, civil engineering, ceramics, et cetera).

Geology has many inter-related subdisciplines, including mineralogy and crystallography, geophysics (seismology, potential fields, remote sensing, et cetera), geochemistry, paleontology (vertebrate, invertebrate, micropaleontology, palynology, paleoenvironmental research, et cetera), petrology (igneous, metamorphic, sedimentary), volcanology, glaciology, stratigraphy, structural geology, geochronology, geomorphology, soil science, engineering geology, hydrogeology, surface-water hydrology, geodynamics and plate tectonics, economic geology, petroleum geology, planetary geology, and oceanography.

References and suggested reading:

  • Brown, G.C., Hawkesworth, C.J., and Wilson, R.C.L., [editors], 1992, Understanding the Earth, a new synthesis: Cambridge, UK, Cambridge University Press, 551 p., ISBN 0-521-42740-1.
  • Duff, D., [editor], 1993, Holmes' Principles of physical geology [4th edition]: London, Chapman and Hall, 791 p., ISBN 0-412-40320-X.
  • Emiliani, C., 1992, Planet Earth -- cosmology, geology, and the evolution of life and environment: Cambridge, UK, Cambridge University Press, 719 p., ISBN 0-521-40949-7.
  • Ernst, W.G., [editor], 2000, Earth systems processes and issues: Cambridge, UK, Cambridge University Press, 566 p., ISBN 0-521-47895-2.
  • Jacobson, M.C., Charlson, R.J., Rodhe, H., and Orians, G.H., 2000, Earth system science from biogeochemical cycles to global change: San Diego, California, Academic Press, 527 p., ISBN 0-12-379370-X.
  • Mathez, E.A., and Webster, J.D., 2004, The Earth machine -- the science of a dynamic planet: New York, Columbia University Press, 335 p., ISBN 0-231-12578-X.
  • Verhoogen, J., Turner, F.J., Weiss, L.E., Wahrhaftig, C., and Fyfe, W.S., 1970, The Earth -- an introduction to physical geology: New York, Holt Rinehart and Winston, 748 p., SBN 03-079655-5.

How old is the Earth?

The current best estimate for the age of the Earth-Moon-meteorite system is 4.51 to 4.55 billion years, with a confidence of 1% or better (Dalrymple, 2001).

The solar nebula cooled to the point at which solid matter could condense by ~4.566 billion years, after which the Earth grew through accretion of these solid particles, the Earth's core developed, and the Moon formed by ~4.51 billion years (Dalrymple, 2001; Allegre and others, 1995; Halliday and Lee, 1999; Tera and Carlson, 1999; Tera, 1981; Patterson, 1956).

The age of the Earth has been known reasonably well since the 1950s, when geochemist Clair Cameron Patterson of CalTech determined it to be 4.550 billion years +/- 70 million years. This age was based on isotopic dating of 5 meteorites and a representative sample of modern Earth lead from a Pacific deep-sea sediment, all of which plot along a linear isochron on a graph of 207Pb/204Pb versus 206Pb/204Pb (Patterson, 1956). Patterson built upon earlier work by Arthur Holmes, E.K. Gerling and F.G. Houtermans (see Dalrymple, 2001; Lewis, 2000). More recent work has generated ages within Patterson's margin of error.

References and suggested reading:

  • Allegre, C.J., Manhes, G., and Gopel, C., 1995, The age of the Earth: Geochimica et Cosmochimica Acta, v. 59, p. 1445-1456.
  • Dalrymple, G.B., 1991, The age of the Earth: Stanford, California, Stanford University Press, 474 p., ISBN 0-8047-2331-1.
  • Dalrymple, G.B., 2001, The age of the Earth in the twentieth century -- a problem (mostly) solved, in Lewis, C.L.E., and Knell, S.J., [editors], The age of the Earth -- from 4004 BC to AD 2002: The Geological Society, London, Special Publication 190, p. 205-221, ISBN 1-86239-093-2.
  • Dalrymple, G.B., 2004, Ancient Earth, ancient skies -- the age of Earth and its cosmic surroundings: Stanford, California, Stanford University Press, ISBN 0-8047-4933-7.
  • Faure, G., 1986, Principles of isotope geology [2nd edition]: New York, John Wiley & Sons, 589 p., ISBN 0-471-86412-9.
  • Halliday, A.N., and Lee, D.C., 1999, Tungsten isotopes and the early development of the Earth and Moon: Geochimica et Cosmochimica Acta, v. 63, p. 4157-4179.
  • Lewis, C., 2000, The dating game -- One man's search for the age of the Earth: Cambridge, UK, Cambridge University Press, 253 p., ISBN 0-521-79051-4.
  • Lewis, C.L.E., and Knell, S.J., [editors], 2001, The age of the Earth -- from 4004 BC to AD 2002: The Geological Society, London, Special Publication 190, 288 p., ISBN 1-86239-093-2.
  • Patterson, C.C., 1956, Age of meteorites and the Earth: Geochimica et Cosmochimica Acta, v. 10, p. 230-237, http://thermo.gg.utk.edu/courses/Ge475/Patterson.html
  • Richardson, S.M., and McSween, H.Y., Jr., 1989, Geochemistry -- pathways and processes: Englewood Cliffs, New Jersey, Prentice-Hall, 488 p., ISBN 0-13-351073-5.
  • Tera, F., 1981, Aspects of isochronism in Pb isotope systematics -- application to planetary evolution: Geochimica et Cosmochimica Acta, v. 45, p. 1439-1448.
  • Tera, F., and Carlson, R.W., 1999, Assessment of the Pb-Pb and U-Pb chronometry of the early Solar System: Geochimica et Cosmochimica Acta, v. 63, p. 1877-1889.

How old is the universe?

The current best estimate for the age of the universe is 13.7 billion years (13,700,000,000 years), with margin of error reported by NASA to be close to 1%. In other words, the team of astrophysicists who published this estimate in 2003 are confident that the universe is between ~13.5 and ~13.9 billion years old, based on their interpretation of reproducibly obtained observational data.

This age was determined through analysis of data obtained by NASA's Wilkinson Microwave Anisotropy Probe (WMAP), a satellite containing sensitive radiation detectors (radiometers) that is orbiting Earth at a distance of ~1 million miles. The radiometers on this satellite measure the cosmic background radiation (CBR): the radiant heat energy emitted as a result of the Big Bang. The CBR is the oldest light in the universe, emitted ~379,000 years after the Big Bang. The WMAP data reproduces and enhances data sets developed using telescope-based systems at the South Pole, at the Mauna Kea Observatories in Hawai'i, as well as data from the COBE satellite and the balloon-borne BOOMERanG radiometers.

Information about how this age was computed can be obtained directly from the WMAP program via their web site. Web sources for other information about the CMB are listed below.

References and suggested reading:

  • Balloon Observations Of Millimetric Extragalactic Radiation ANd Geophysics (BOOMERanG) home page (http://cmb.phys.cwru.edu/boomerang/)
  • Caltech Observational Cosmology Group home page (http://www.astro.caltech.edu/~lgg/), which includes information about BOOMERanG and other projects associated with the study of the birth and evolution of the universe, including measurement and characterization of the cosmic background radiation
  • NASA's Legacy Archive for Microwave Background Data Analysis (LAMBDA) home page (http://lambda.gsfc.nasa.gov/), with links to active web resources for WMAP, COBE, and other projects and data sets related to the measurement and characterization of the cosmic background radiation.
  • Penrose, R., 2005, The road to reality -- a complete guide to the laws of the universe: New York, Knopf, 1099 p., ISBN 0-679-45443-8
  • Raymo, Chet, 2001, An intimate look at the night sky: New York, Walker and Company, 242 p., ISBN 0-8027-7670-1
  • Smoot, G.F., and others, 1991, Preliminary results from the COBE differential microwave radiometers -- large-angular-scale isotropy of the Cosmic Microwave Background: Astrophysics Journal, v. 371, L1.
  • Spergel, D.N., and others, 2003, First year Wilkinson Microwave Anisotropy Probe (WMAP) observations -- determination of cosmological parameters: Astrophysics Journal Supplement, v. 148, p. 175.
  • Weinberg, S., 1988, The first three minutes -- a modern view of the origin of the universe [updated edition]: New York, Basic Books, 198 p., ISBN 0-465-02436-X.

Are decay constants actually constant?

The question commonly arises whether the decay constants used in the isotopic dating of geological materials are actually constant, or do they vary in response to some external force?

The answer is that the decay constants used in the dating of geological materials are effectively constant and invariant to external forces.

The behavior of radioactive isotopes has been the focus of international scientific study since they were first recognized by Henri Becquerel in the late Nineteenth Century, and that behavior is now well understood.

The primary isotopes used to date rocks and minerals are given in the following table (Dalrymple, 1991, p. 80; Faure, 1986):

Parent
Isotope
Daughter
Isotope
Decay
Constant
Decay
Mechanism(s)
40K 40Ar 5.81x10-11 per year electron capture
87Rb 87Sr 1.42x10-11 per year beta decay
147Sm 143Nd 6.54x10-12 per year alpha decay
176Lu 176Hf 1.93x10-11 per year beta decay
187Re 187Os 1.612x10-11 per year beta decay
232Th 208Pb 4.948x10-11 per year alpha and beta decay in series
235U 207Pb 9.8485x10-10 per year alpha and beta decay in series
238U 206Pb 1.55125x10-10 per year alpha and beta decay in series

(K=potassium, Ar=argon, Rb=rubidium, Sr=strontium, Sm=samarium, Nd=neodymium, Lu=lutetium, Hf=hafnium, Re=rhenium, Os=osmium, Th=thorium, Pb=lead, U=uranium)

The mechanisms of radioactive decay that are relevant to the dating of geological materials include beta decay, electron capture and alpha decay. The effect of beta decay is that a neutron is converted to a proton within an atom's nucleus, accompanied by the ejection of an electron and an antineutrino from the atom. For a given atom, beta decay leads to an increase in atomic number by 1, and no change in the atomic mass number. Electron capture has the opposite effect, and occurs when an electron from the innermost orbital of an atom is captured by the nucleus, leading to the conversion of a proton into a neutron. For a given atom, electron capture leads to a decrease in atomic number by 1, and no change in the atomic mass number. Heavier radiogenic elements may undergo alpha decay, in which two protons and two neutrons are ejected from the nucleus, reducing the atomic number by 2 and the atomic mass number by 4.

The possible effects of changing temperature, pressure, chemical state, and electric or magnetic field strength on the three decay mechanisms relevant to geologic dating have been intensively studied, both theoretically and experimentally. These studies have shown that changing environmental conditions have either no measurable effect or a negligible effect (less than 1%, and that only for 7Be, which decays through electron capture) on the rate at which the decay processes occur (Dalrymple, 1991, p. 86-90). "There is no evidence that decay constants have changed as a function of time during the history of the solar system" (Faure, 1986, p. 41).

References and suggested reading:

  • Dalrymple, G.B., 1991, The age of the Earth: Stanford, California, Stanford University Press, 474 p., ISBN 0-8047-2331-1.
  • Dalrymple, G.B., 2004, Ancient Earth, ancient skies -- the age of Earth and its cosmic surroundings: Stanford, California, Stanford University Press, ISBN 0-8047-4933-7.
  • Emery, G.T., 1972, Perturbation of nuclear decay rates: Annual Reviews of Nuclear Science, v. 22, p. 165-202.
  • Faure, G., 1986, Principles of isotope geology [2nd edition]: New York, John Wiley & Sons, 589 p., ISBN 0-471-86412-9.
  • Hensley, W.K., Bassett, W.A., and Huizenta, J.R., 1973, Pressure dependence of the radioactive decay constant of beryllium-7: Science, v. 181, p. 1164-1165.
  • Hopke, P.K., 1974, Extranuclear effects on nuclear decay rates: Journal of Chemical Education, v. 51, p. 517-519.
  • Richardson, S.M., and McSween, H.Y., Jr., 1989, Geochemistry -- pathways and processes: Englewood Cliffs, New Jersey, Prentice-Hall, 488 p., ISBN 0-13-351073-5.

What is a fossil?

A fossil is a naturally occurring artifact of ancient life. (A bone from a recently deceased chicken found in your back yard would not be considered a fossil, nor would a footprint in concrete.)

Examples of types of fossils include:

  • entire organisms frozen in glaciers or in permafrost
  • shells and bones
  • casts or molds of hard parts
  • footprints, burrows, root casts
  • plant fossils, including wood replaced by silica precipitated from ground water
  • permineralized feces (coprolites)

Fossils range in size from quite large (e.g., fossil tree trunks and dinosaur bones) to microscopic fossils (microfossils) and pollen.

The most common types of fossils are marine invertebrates (animals with shells) and microfossils. Animals that lived on dry land are much less likely to be preserved as fossils.

References and suggested reading:

  • Callomon, J.H., 2001, Fossils as geological clocks, in Lewis, C.L.E., and Knell, S.J., [editors], The age of the Earth -- from 4004 BC to AD 2002: The Geological Society, London, Special Publication 190, p. 237-252, ISBN 1-86239-093-2.
  • Clarkson, E., 1998, Invertebrate paleontology and evolution [4th edition]: Oxford, UK, Blackwell Science, 468 p., ISBN 0-632052384.Cooper, J.D., Miller, R.H., and Patterson, J., 1986, A trip through time -- principles of historical geology: Columbus, Ohio, Merrill Publishing Company, 469 p., ISBN 0-675-20140-3.
  • Prothero, D.R., 1997, Bringing fossils to life: an introduction to paleobiology: New York, McGraw-Hill, 480 p., ISBN 0-070521972.
  • Rudwick, M.J.S., 1976, The meaning of fossils -- episodes in the history of paleontology: Chicago, University of Chicago Press, 285 p., ISBN 0-226-73103-0.
  • Stanley, S.M., 1986, Earth and life through time: New York, W.H. Freeman and Company, 690 p., ISBN 0-7167-1677-1.

How old are the oldest fossils?

The metasedimentary rocks associated with the early Archaean-aged Itsaq Gneiss Complex on Akilia Island, southwestern Greenland, are reported to contain graphite microparticles that are depleted in 13C that have been interpreted to be the products of organic life (McGregor and Mason, 1977; Mojzsis and others, 1996; Nutman and others, 1996, 1997; Mojzsis and Harrison, 1999). The 13C-to-12C ratio in the graphite microparticles is essentially the same as in modern organisms (Stanley, 1986). These graphite particles were originally thought to be ~3.83-3.85 billion years in age (Nutman and others, 1997; Mojzsis and Harrison, 2002), but a recent review of the relevant geological and isotopic evidence by Kamber and others (2001) concludes that the graphite is contained in rock that is 3.65 to 3.70 billion years old.

A second occurrence of isotopically light graphite microparticles within graded beds in the Isua supracrustal belt of southwestern Greenland may provide better evidence of the earliest life on Earth, from ?3.7 billion years ago (Rosing, 1999; Lepland and others, 2005).

Other fossils reported from the Archean Eon, 4.6 to 2.5 billion years ago, include:

  • 3.5 billion year old filaments of cyanobacteria (blue-green algae) from the Warrawoona Group at North Pole, western Australia
  • 3.4-3.5 billion year old stromatolites composed of cyanobacteria and sediment from the Pilbara Shield of Australia
  • 3-3.4 billion year old spheroidal structures resembling cyanobacteria from the Fig Tree Group of the Barberton Mountain region of southern Africa
  • 3 billion year old stromatolites from the Pongola Supergroup of southern Africa
  • 2.8 billion year old stromatolites from the Bulawayan Group of Rhodesia

(after Stanley, 1986, p. 262-263, and Cooper and others, 1986, chapter 9).

The earliest life forms on Earth were simple procaryotes that could tolerate extreme environmental conditions and that reproduced asexually by cell division, similar to modern archaeobacteria. Cyanobacteria capable of photosynthesis were prevalent from 3.5 billion years, and persist today (Emiliani, 1992, chapter 19). Green algae -- the first eucaryotic organisms capable of sexual reproduction -- developed ~1.5 billion years ago, at least 2 billion years after the first procaryotes.

References and suggested reading:

  • Cairns-Smith, A.G., 1985, Seven clues to the origin of life: Cambridge, UK, Cambridge University Press (Canto edition, 1990), 131 p., ISBN 0-521-39828-2.
  • Callomon, J.H., 2001, Fossils as geological clocks, in Lewis, C.L.E., and Knell, S.J., [editors], The age of the Earth -- from 4004 BC to AD 2002: The Geological Society, London, Special Publication 190, p. 237-252, ISBN 1-86239-093-2.
  • Cooper, J.D., Miller, R.H., and Patterson, J., 1986, A trip through time -- principles of historical geology: Columbus, Ohio, Merrill Publishing Company, 469 p., ISBN 0-675-20140-3.
  • Dyson, F., 1999, Origins of life [2nd edition]: Cambridge, UK, Cambridge University Press, 100 p., ISBN 0-521-62668-4.
  • Emiliani, C., 1992, Planet Earth -- cosmology, geology, and the evolution of life and environment: Cambridge, UK, Cambridge University Press, 717 p., ISBN 0-521-40949-7.
  • Lepland, A., van Zuilen, M.A., Arrhenius, G., Whitehouse, M.J., and Fedo, C.M., 2005, Questioning the evidence for Earth's earliest life -- Akilia revisited: Geology, v. 33, p. 77-79.
  • McGregor, V.R., and Mason, B., 1977, Petrogenesis and geochemistry of metabasaltic and metasedimentary enclaves in the Amitsoq gneisses, west Greenland: American Mineralogist, v. 62, p. 887-904.
  • Mojzsis, S.J., and Harrison, T.M., 1999, Geochronological studies of the oldest known marine sediments, in Ninth Annual V. M. Goldschmidt Conference: Lunar and Planetary Institute, Houston, Contribution No. 971, p. 201-202.
  • Mojzsis, S.J., and Harrison, T.M., 2002, Establishment of a 3.83-Ga magmatic age for the Akilia tonalite (southern West Greenland): Earth and Planetary Science Letters, v. 202, p. 563-576.
  • Mojzsis, S.J., Arrhenius, G., McKeegan, K.D., Harrison, T.M., Nutman, A.P., and Friend, C.R.L., 1996, Evidence for life on Earth before 3800 million years ago: Nature, v. 384, p. 55-59.
  • Nutman, A.P., McGregor, V.R., Friend, C.R.L., Bennett, V.C., and Kinny, P.D., 1996, The Itsaq Gneiss Complex of southern west Greenland -- the world's most extensive record of early crustal evolution (3,900-3,600 Ma): Precambrian Research, v. 78, p. 1-39.
  • Nutman, A.P., Mojzsis, S.J., and Friend, C.R.L., 1997, Recognition of ?3850 Ma water-lain sediments in West Greenland and their significance for the early Archaean Earth: Geochimica et Cosmochimica Acta, v. 61, p. 2475-2484.
  • Rosing, M.T., 1999, 13C-depleted carbon microparticles in ?3700-Ma sea-floor sedimentary rocks from West Greenland: Science, v. 283, p. 674-676.
  • Stanley, S.M., 1986, Earth and life through time: New York, W.H. Freeman and Company, 690 p., ISBN 0-7167-1677-1.

What are mass extinctions, and when have they occurred?

A mass extinction is "an extinction of a significant proportion of the world's biota in a geologically insignificant period of time" (Hallam and Wignall, 1997).

The evidence of such an event is contained in the fossil record. If, for example, fossils of species A through Z are present in rocks just older than, say, 200 million years, but only fossils of species K and U are present in rocks younger than 200 million years, we would infer that the other 24 species had become extinct at ~200 million years.

The fossil record is most complete for the time interval known by geologists as the Phanerozoic, which extends from ~542 million years ago to the present. Organisms whose structure includes hard parts (either shells or bones) are first found in the fossil record at the beginning of the Phanerozoic, which is significant because hard parts are much more likely to leave their mark in the fossil record than the soft tissues of organisms.

The major mass extinction events of the Phanerozoic include the following (after Lucas, 2005; Raup and Sepkoski, 1982, 1984; Courtillot, 1999):

  • 450 Myr (Late Ordovician)
    • estimated 85% of marine species became extinct
  • 374 Myr (Late Devonian)
    • estimated 70-80% of marine species became extinct
  • 251 Myr (end of the Permian)
    • estimated 90% of all species became extinct, perhaps 99% of all animals -- the greatest mass extinction known in Earth history
  • 200 Myr (end of the Triassic)
    • most ammonites, half the genera of bivalves, many brachiopods and gastropods, 20% of foraminifera families, 80% of quadrupeds, and all conodonts became extinct
  • 65 Myr (end of the Cretaceous)
    • dinosaur extinction, along with ~2/3 of all species and perhaps 80% of all individual organisms

Many other less profound extinction events have been documented throughout the Phanerozoic, and these events commonly mark the boundaries between geological periods. Subsequent to extinction events, speciation (the development of new species from pre-existing forms) is typically enhanced as organisms adapted to the environmental niches left vacant by extinct species.

There is no single cause for all mass extinctions, and indeed many individual mass extinctions may be the result of an unfortunate combination of causes. Significant environmental changes worldwide (e.g., changes in the temperature or chemistry of the oceans or atmosphere, changes in the amount of solar radiation that reaches Earth) inevitably result in dramatic changes in Earth's biosphere. Some of the mechanisms that may result in such changes, and that have been discussed as contributors to mass extinction, include the following:

References and suggested reading:

  • Alvarez, L.W., Alvarez, W., Asaro, F., and Michel, H.V., 1980, Extraterrestrial Cause for the Cretaceous-Tertiary boundary: Science, v. 208, p. 1095-1108.
  • Callomon, J.H., 2001, Fossils as geological clocks, in Lewis, C.L.E., and Knell, S.J., [editors], The age of the Earth -- from 4004 BC to AD 2002: The Geological Society, London, Special Publication 190, p. 237-252, ISBN 1-86239-093-2.
  • Clarkson, E., 1998, Invertebrate paleontology and evolution [4th edition]: Oxford, UK, Blackwell Science, 468 p., ISBN 0-632052384.
  • Cooper, J.D., Miller, R.H., and Patterson, J., 1986, A trip through time -- principles of historical geology: Columbus, Ohio, Merrill Publishing Company, 469 p., ISBN 0-675-20140-3.
  • Courtillot, V., 1999, Evolutionary catastrophes -- the science of mass extinction: Cambridge, UK, Cambridge University Press, 173 p., ISBN 0-521-58392-6.
  • Hallam, A., and Wignall, P.B., 1997, Mass extinctions and their aftermath: Oxford, UK, Oxford University Press, 328 p., ISBN 0-198549164.
  • Lucas, S.G., 2005, 25 years of mass extinctions and impacts: Geotimes, February, p. 28-32.
  • Officer, C., and Page, J., 1996, The great dinosaur extinction controversy: Reading, Massachusetts, Addison-Wesley Publishing Company, 209 p., ISBN 0-201-48384-X.
  • Prothero, D.R., 1997, Bringing fossils to life: an introduction to paleobiology: New York, McGraw-Hill, 480 p., ISBN 0-070521972.
  • Raup, D., 1991, Extinction -- bad luck or bad genes: New York, W.W. Norton & Company, 210 p., ISBN 0-393-03008-3.
  • Raup, D. M. and Sepkoski, J. J., Jr., 1982, Mass extinctions in the marine fossil record: Science, v. 215, p. 1501-1503.
  • Raup, D.M., and Sepkoski, J.J., Jr., 1984, Periodicity of Extinctions in the Geologic Past: Proceedings of the National Academy of Sciences (USA), v. 81, p. 801-805.
  • Raup, D.M., and Sepkoski, J.J., Jr., 1986, Periodic Extinction of Families and Genera: Science, v. 231, p. 833-836.
  • Schwartz, J.H., 1999, Sudden origins -- fossils, genes, and the emergence of species: New York, John Wiley and Sons, 420 p.
  • Stanley, S.M., 1986, Earth and life through time: New York, W.H. Freeman and Company, 690 p., ISBN 0-7167-1677-1.
  • Ward, P.D., 1992, On Methuselah's trail -- living fossils and the great extinctions: New York, W.H. Freeman & Company, 212 p., ISBN 0-7167-2203-8.
    • massive volcanism (eruption of flood basalts) and consequent alteration in atmosphere/ocean chemistry
    • impact of meteorites
    • variations in sea level
    • significant glaciation
    • release of methane or carbon dioxide due to melting of gas hydrates
    • changes in the large scale circulation of ocean water as the shape/continuity of ocean basins change due to plate motion
    • radiation from a nearby supernova

Does the fossil record support the idea of biological change over time (biological evolution)?

Yes. The fossil record clearly indicates

  • a progression in complexity of organisms from very simple fossil forms in the oldest rocks (>3.5 billion years old) to a broad spectrum from simple to complex forms in younger rocks,
  • that some organisms that were once common are now extinct, and
  • that the living organisms inhabiting our world today are similar (but generally not the same) as organisms represented as fossils in young sedimentary deposits, which in turn have evolutionary ancestors represented as fossils in yet older rocks.

Mammals, for example, are prevalent today and can be traced back in the fossil record for approximately 200 million years, but are not present as mammals in the fossil record before that; however, fossil forms that have reasonably been interpreted to be associated with the evolutionary precursors to mammals are found in older rocks.

Whether biological evolution occurs has not been a matter of scientific debate for more than a century. It is considered a proven fact. The specific mechanisms of biological change over time continue to be a topic of active research, and include mechanisms proposed by Charles Darwin as well as more recently developed ideas based on our growing knowledge of genetics and molecular biology. Using the methods of modern science, our knowledge of the fundamental mechanisms of life has grown enormously since the initial characterization of the role of DNA in reproduction, inheritance and evolution in the mid-1950s.

The American Geological Institute and The Paleontological Society, partnering with the most respected geoscience societies in America including the Geological Society of America, the American Geophysical Union, and the American Association of Petroleum Geologists (among others), have produced a booklet on evolution and the fossil record that can be downloaded as a PDF file. This booklet was written for the general public by people who have worked with the fossil record throughout their careers, and was thoroughly reviewed by other professional geologists and paleontologists.

DOWNLOAD the 1 MB PDF file Evolution and the Fossil Record by Pojeta and Springer.

Read the statement on evolution by the Baylor University Department of Biology.

View the web version of the report Science and Creationism: A View from the National Academy of Sciences, Second Edition (1999), published by the U.S. National Academy of Sciences (www.nap.edu/books/0309064066/html/25.html) or explore other resources about evolution from the National Academy's web site.

You can also access position statements and other web resources from the American Geological Institute, the Geological Society of America, the American Geophysical Union, and the American Association for the Advancement of Science.

References and suggested reading:

  • Cairns-Smith, A.G., 1985, Seven clues to the origin of life: Cambridge, UK, Cambridge University Press (Canto edition, 1990), 131 p., ISBN 0-521-39828-2.
  • Carroll, Sean B., 2005, Endless forms most beautiful: The new science of evo devo and the making of the animal kingdom: New York, W.W. Norton & Co., 350 p., ISBN 0-393-06016-0.
  • Cooper, J.D., Miller, R.H., and Patterson, J., 1986, A trip through time -- principles of historical geology: Columbus, Ohio, Merrill Publishing Company, 469 p., ISBN 0-675-20140-3.
  • Dawkins, R., 1995, River out of eden -- a Darwinian view of life: New York, Basic Books, 172 p., ISBN 0-465-01606-5.
  • Dyson, F., 1999, Origins of life [2nd edition]: Cambridge, UK, Cambridge University Press, 100 p., ISBN 0-521-62668-4.
  • Eldredge, N., 2000, The pattern of evolution: New York, W.H. Freeman and Company, 219 p., ISBN 0-7167-3963-1.
  • Emiliani, C., 1992, Planet Earth -- cosmology, geology, and the evolution of life and environment: Cambridge, UK, Cambridge University Press, 717 p., ISBN 0-521-40949-7.
  • Gould, S.J., 1989, Wonderful life -- the Burgess shale and the nature of history: New York, W.W. Norton & Company, 347 p., ISBN 0-393-02705-8.
  • Kardong, K.V., 2005, An introduction to biological evolution: New York, McGraw-Hill Higher Education, 322 p., ISBN 0-07-238579-0.
  • Lewin, R., and Foley, R.A., 2004, Principles of human evolution [2nd edition]: Oxford, UK, Blackwell Publishing, 555 p., ISBN 0-632-04704-6.
  • Marks, J., 2002, What it means to be 98% chimpanzee -- apes, people, and their genes: Berkeley, California, University of California Press, 312 p., ISBN 0-520-24064-2.
  • Miller, K., 2000, Finding Darwin's God: Harper Collins Publishers, 352 p., ISBN 0060930497
  • Olson, S., 2002, Mapping human history -- genes, race and our common origins: New York, Mariner Books, 292 p., ISBN 0-618-35210-4.
  • Pojeta, J., Jr., and Springer, D.A., 2001, Evolution and the fossil record: Alexandria, Virginia, American Geological Institute, 27 p., ISBN 0-922152-57-8, https://www.agiweb.org/news/evolution.pdf
  • Schwartz, J.H., 1999, Sudden origins -- fossils, genes, and the emergence of species: New York, John Wiley & Sons, 420 p., ISBN 0-471-37912-3.
  • Scott, E.C., 2004, Evolution vs. creationism -- an introduction: Berkeley, University of California Press, 272 p., ISBN 0-520-24650-0.
  • Stanley, S.M., 1986, Earth and life through time: New York, W.H. Freeman and Company, 690 p., ISBN 0-7167-1677-1.
  • Wells, S., 2002, The journey of man, a genetic odyssey: New Jersey, Princeton University Press, 224 p., ISBN 0-691-11532-X.

 

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