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113 Cards in this Set
- Front
- Back
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dramatic geologic events
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Earthquakes
1906 San Francisco 1959 Yellowstone Park 1964 Alaskan 2004 Sumatran Earthquake [~800,000 quakes/year resulting in ~10,000 deaths/year] |
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subtle geologic events
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-plate tectonics
-deposition of sediments -erosion and weathering -climate change -glacial cycles and sea level changes (building and melting of ice sheets) -crustal changes (glacial rebound) |
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geologic rates
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fastest: 25,000 mm/yr-advance of the tigris euphrates river delta
10mm/yr-rise of scandinavia from glacial isostatic rebound 5mm/yr-post glacial rise of sea level 0.7mm/yr- cutting of the grand canyon slowest: 0.03 mm/yr-avg erosion rate of the continent |
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1 million seconds
1 billion seconds |
11.8 days
32 years |
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linear change
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rate of change remains constant over time, e.g. uplift rates
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nonlinear change
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rate of change increases exponentially, e.g. population growth
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nonrepeating change
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unidirectional change with irreversible alterations
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repeating changes (periodic or rhythmic)
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predictable changes such as tides and seasons
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episodic changes
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events that do not occur with regular time intervals, such as floods or meteorite impacts
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catastrophic view of change
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1654
Anglican archbishop Usher calculated earth created 10/23/4004 bc (at 9am) and flood at 2349 bc, earth could only be 6000 years old |
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Uniformitarianism
uniform view of change |
late 1700's and early 1800's
James Hutton (considered father of geology) floods, earthquakes and volcanic eruptions common events not catastrophic equilibrium-all geologic processes are competing with one another to produce a situation tending toward balance; due to Earth's dynamic nature, balance is rarely maintained for long spans of geologic time |
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major issues of historical geology
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1-rates of change and time (how do you convince someone Earth is older than 6000 years)
2-scientific method (how does it assist with reasoning, is it objective?) 3-belief vs scientific thought 4-respecting beliefs and avoiding paradigms |
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events with worldwide evidence
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bolide impact at KT boundary
-irridium found world wide in sediments large volcanoes -worldwide distribution of ash |
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what is a fossil
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preserved record of life that may include shells, teeth, skeletons, plant remains, burrows, trackways, ect...
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Body fossil
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– part of the living organism preserved in the rock record, e.g. skeleton, shell
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Trace fossil
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– markings left by an organism, eg. trackway.
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Skeletal Limestone
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[contains abundant fossils of coral, brachiopods, clams, and bryozoans; Knife is 9 cm long]
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Leonardo da Vinci (~1500 A.D.)
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Recognized fossils in sedimentary rocks associated with marine environments
Identified several discrete horizons of marine fossils – this suggests multiple events rather than one flood! |
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Steno
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principle of superposition, original horzontality, and lateral continuity
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Principle of Superposition
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– Sedimentary rock units are deposited in a sequence, with the oldest sedimentary rock layers on the bottom.
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Principle of Original Horizontality
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–Sedimentary layering that is not horizontal has been tilted or uplifted.
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Principle of Lateral Continuity
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– Sedimentary rocks are deposited in widespread depositional layers with a unique composition.
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John Woodward
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Published a map of mineral deposits in England in 1723.
Predictable distribution must be related to some natural process. |
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William Smith
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Canal builder that recognized that certain fossils occurred in particular layers of sedimentary rock; recognized a predictable pattern.
Published his first geologic map of England in 1815. |
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George Cuvier & Alexandre Brongniart (Brong-nee-are)
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Independent of Smith, used fossils to map the distribution of various strata in France
Published a geologic map of France in 1811. After ~1810, fossils in sedimentary rock strata are used to map the distribution of rock units in Europe. |
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Principle of Fossil Correlation
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– like assemblages of fossils are of like age, and therefore the strata containing them are also of like age.
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Index Fossil
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– useful for the correlation of strata from place to place. An index fossil must be:
easily recognizable widespread in occurrence restricted to a very limited thickness of strata |
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Catastrophism
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In 1811, George Cuvier recognized abrupt changes in fossil assemblages separated by unconformities within sedimentary rock strata. He proposed that widespread catastrophes resulted in the extinction of selected organisms (all organisms that ever lived were created first).
Cuvier also noted that fossils in younger strata were more like living organisms, so these extinctions eliminated prehistoric species. |
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Catastrophism
Alcide D’Orbignay (Door-ig-nay) |
postulated in 1859 that new species were created after each of the catastrophes rather than selective extinctions. Developed the theory, Catastrophism and Special Creations, which stated that there was little or no connection between the index fossils of successive groups of strata.
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Cosmogonists
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Establish all-encompassing hypotheses to explain the origin and development of the Earth. Cosmogonists assumed:
The Earth was originally hot and glowed like the sun As the earth cooled, a primitive, hard crust formed Water and atmosphere became segregated according to their relative densities Earth’s interior had a fiery core surrounded concentrically by solid material. |
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Cosmogonists
G. L. de Buffon |
In 1749 published Histoire Naturelle and challenged the literal “six days of creation” in the Bible.
Postulated that cooling of the Earth took place over six distinct epochs lasting approximately 75,000 years. His estimate was calculated from cooling experiments of steel balls as an analogue for the cooling of the Earth. |
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Cosmogonists
Giovanni Arduino (Are-dwee-no) |
In 1759, proposed three major subdivisions for rocks in northern Italy:
Primitive Mountains - unfossiliferous schists & altered sedimentary rocks in the high Alpine mountain core Secondary Mountains - limestones and shales containing fossils Tertiary Mountains - richly fossiliferous clay, sand, and limestone of the low hills Volcanic Rocks - Youngest |
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Neptunism
Abraham G. Werner |
In 1787, Werner published a general theory for the Earth’s crust that resulted from the precipitation from seawater.
Proposed that as the seas retreated, rocks were precipitated according to the following groupings: Primitive (granite, schist, gneiss), Transition (graywacke, slate, limestone with first organic fossils) Secondary (sandstone, limestone, coal, basalt) Alluvial (loose gravel, sand, peat) |
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Basalt Controversy
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Neptunists, especially Werner, suggested that basalt within sedimentary sequences had been precipitated from seawater of the universal ocean.
Basalt that resembled a lava flow within sedimentary sequences had been fused by combustion of adjacent coal seams. The linkage of basalt to volcanoes and lava flows instead of chemical precipitation from seawater resulted in the abandonment of this idea. |
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Plutonism
James Hutton |
Scottish gentleman farmer and geologist
Proposed the Earth was ever changing, “no vestige of a beginning, no prospect of an end.” Hypothesized the origin of granite & basalt from a molten magma that cooled slowly. This was also supported by experimentation by Sir James Hall who melted basalt between 800o and 1200oC, which produced glass upon rapidly cooling and basalt on slow cooling. |
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Upheaval of Mountains
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Hutton observed unconformities separating tilted rocks from overlying horizontal strata.
Hutton proposed rejuvenation of the Earth’s surface by repeated cycles of erosion and deposition followed by upheavals. Hutton published Theory of the Earth in 1795. These theories conflicted with the catastrophic views of the day; these concepts also conflicted with the literal interpretation of the Scriptures; “no science is valid unless it supports the Scriptures.” |
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Uniformitarianism
Charles Lyell |
Proposed that the same processes operating today acted for all of Earth’s History; Uniformitarianism – “the present is the key to the past”.
Published Principles of Geology, which was revised 12 times between 1830 and 1875. Lyell refined his views to suggest that the rock record and changes at the Earth’s surface occur gradually over long periods of time; this yielded the philosophy of Gradualism. |
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Scientific Method & Modern Geology
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Scientific approach revolutionized geology in the 19th century; observation, multiple working hypotheses, experimentation, and hypothesis refinement provided a foundation for the new science, geology.
Modern geology includes parts of each of these major philosophies from the 19th century. Actualism –modern doctrine of uniformity to the study of geology, which includes rapid and sudden events such as the formation of the Scablands of eastern Washington by catastrophic flooding, proposed by J. Harlen Bretz. |
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Actualism
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–modern doctrine of uniformity to the study of geology, which includes rapid and sudden events such as the formation of the Scablands of eastern Washington by catastrophic flooding, proposed by J. Harlen Bretz.
and meteor impacts |
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Classification of Biological Organism
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In 1749, George de Buffon published Histoire Naturelle. Species – produce viable offspring
Linnaeus in 1758 proposed biological classification of organisms based upon similar characteristics |
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Evolution & Lamarck (1744-1829)
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Coined the term biology
Inheritance of Acquired Characteristic Phylogeny – evolutionary history of an organism |
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Evolution
Charles Darwin |
Sailed on the H. M. S. Beagle from 1831-1836.
Explored the south Pacific and visited the Galápagos Islands In 1859, published Origin of Species by means of Natural Selection. Natural Selection – “survival of the fittest” – the best adapted, the more likely to be successful and produce offspring Evolution - continuous, unidirectional change |
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Evidence for Evolution
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Classification of Biological Organisms
Homology – similar structures among groups of organisms, e.g. bones in the arm of animals. Vestigial Structures – structures that no longer are used by an organism; relict to their evolutionary history, e.g., appendix & stunted tail in humans Embryonic History – the developmental stages of biological organisms are similar Biogeography – organisms on different continents belong to different groups |
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Genetics - 20th Century
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1930’s work with fruit flies established that changes in genes result in mutations, most of which are harmful or life threatening.
Large-scale changes from gene alterations are called macromutations – leading to new biological forms. Synthetic Theory of Evolution or Neo-Darwinism developed from genetic studies suggesting that natural selection could result in evolutionary change. |
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Genetics - Modern Genetics
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Genotype – populations of organisms vary because each member has a different genetic code
Genetic code – within the nucleus of every cell (DNA-deoxyribonucleic acid) Variations in genotype are reflected in physical characteristics of individual – phenotype (e.g. hair color, eye color) |
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Genetics - 19th Century
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Gregor Mendel (1822-1884) – developed the basic laws of heredity from studying pea plants
Mendel published his work in 1865, but the work was considered obscure – too much mathematical modeling! Mendel is considered the first true geneticist |
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Genetic Variations
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Strands of DNA become twisted, reversed, deleted, or duplicated resulting in new genetic code
Recombination – sexual reproduction and the combination of 2 genetic codes (must be the same species) Examples: Peppered moth of England (bird predation) Giraffes – natural selection through mutation |
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Ernst Mayr in the 1940’s
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Large populations – tend to be genetically stable; in contrast, small populations evolve rapidly, especially along the periphery of geographic range
Geographic Barrier (genetic isolation) – formation of a new ocean basin or uplift of mountain belts, isolating species of animals Allopatric – new species form when a larger population is spilt into subpopulations Sympatric – continually interbreeding with little chance to differentiate genetically |
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Sympatric
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– continually interbreeding with little chance to differentiate genetically
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Allopatric
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– new species form when a larger population is spilt into subpopulations
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Evolution in the Fossil Record
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Phyletic Gradualism – morphologic changes occur very slowly through time; no gigantic leaps in morphology.
Punctuated Equilibrium (Niles Elridge & Stephen J. Gould, 1972) – morphologic changes are rapid over short periods of time, and then remain more-or-less unchanged. |
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Evolution in the Fossil Record
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Divergence – organisms speciate and develop traits that differentiate them from their ancestors.
Adaptive Radiation – evolutionary “explosion” of organisms that fill and “fit” into every niche; Convergence – unrelated organisms that have independently converged on the same body form and fill a similar ecological niche Iterative evolution – the development of a particular morphology several times in the geologic record by different organisms |
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Iterative evolution
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– the development of a particular morphology several times in the geologic record by different organisms
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Adaptive Radiation
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– evolutionary “explosion” of organisms that fill and “fit” into every niche;
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Convergence
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– unrelated organisms that have independently converged on the same body form and fill a similar ecological niche
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Relative Age Dating
Basic Principles |
Superposition
Original Horizontality Lateral Continuity Cross-Cutting Relationships (Corollary to Superposition) Inclusions (Corollary to Superposition) Fossil Succession |
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Relative Age Dating
Basic Sedimentary Rock Relationships |
Facies Change (Intertonguing)
Unconformities Thickness Variations |
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methods to describe geologic structures in the field
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rock type
1- color 2-attitude (how is the sedimentary layer oriented?) 3-minerals (hand specimen, can often be finished in the lab) 4- fossils 5- location all of which allows outcrops to be correlated (or not) with outcrops in other areas |
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Relative Age Dating
Missing time from the rock record |
Bedding Plane – separates each layer of sedimentary rock; interlude between depositional events.
Hiatus – an extended period of nondeposition Unconformity – large intervals of missing time with erosional truncation (angular unconformity, nonconformity, disconformity) |
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Unconformity
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– large intervals of missing time with erosional truncation (angular unconformity, nonconformity, disconformity)
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Hiatus
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– an extended period of nondeposition
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Bedding Plane
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– separates each layer of sedimentary rock; interlude between depositional events.
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Basic units of the sedimentary rock record
Formation |
– Local to regional, mappable sedimentary rock unit distinguished by one or more characteristic properties (lithology) typically named for a geographic region
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Basic units of the sedimentary rock record
Sedimentary Facies |
– lateral variations within a formation, each facies has a unique set of characteristics such as sedimentary structures or fossils.
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Migration of shorelines
Transgressive facies pattern |
– encroachment of the sea resulting in a shift of depositional systems landward.
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Migration of shorelines
Regressive facies pattern |
– shifting of depositional environments seaward either by a sea level drop or by progradation (deposition) of sediments.
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Sedimentary Facies and Fossils
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Fossils permit the correlation of age equivalent strata, even if the two are completely different sedimentary facies.
Organisms that are swimmers or floaters are the most widespread and may be included among numerous sedimentary facies, permitting correlation from one formation to the next. |
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Unconformity Types
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nonconformity
disconformity angular unconformity |
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Nonconformity
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– sedimentary rocks overlying metamorphic or igneous rocks
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Disconformity
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– little or no angular discordance between sedimentary rocks above and below the erosional surface
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Angular Unconformity
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– Sedimentary rocks meet the overlying sedimentary strata at an angle along the erosional surface.
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Radiometric Age Dating
Basic Principles: |
Radioactive Decay
Parent Radioactive Isotope Stable Daughter Isotope Decay Rate Half-life |
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Types of Radioactive Decay
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alpha, beta, electron capture
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Alpha decay
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– loss of 2 neutrons & 2 protons (alpha particle) from the nucleus of a radioactive isotope
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Beta decay
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– loss of an electron from the nucleus of the radioactive isotope
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Electron capture
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– nucleus of the radioactive isotope receives an electron;
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Radiometric Age Dating
Daughter-Isotope Ratios |
Daughter isotopes are formed at different rates, therefore their ratios change in a mathematically predictable way.
Separate ratios of the three radiogenic lead isotopes to nonradiogenic 204Pb, when extrapolated back to their presumed primordial ratios, provide the best estimate of the total age of earth at 4.6 to 4.7 billion years. |
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Dating with carbon-14 (radiocarbon dating):
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Half-life of 5730 years
Used to date very recent events, last 60,000 years (Why?) Radiogenic 14C is produced by the interaction of cosmic radiation with nitrogen in the upper atmosphere Useful tool for anthropologists, archeologists, and geologists who study very recent Earth history |
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Radiometric Age Dating
Fission Track Dating |
Relative density of tracks resulting from radiation damage by passing fission particle
Density of tracks increases with age Typically measured in zircons |
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Radiometric Age Dating
Blocking Temperature |
– cooling threshold below which a given mineral becomes a closed chemical system:
Slow or delayed cooling – yield dates that may be younger than the initial time of crystallization Resetting of the isotopic clock – if the blocking temperature is exceeded, the stable daughter product may be released from the mineral grain |
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Radiometric Age Dating
Discordant Dates |
– results from disturbance of isotope ratios:
Leakage of daughter (gaseous Ar or He) Differential purging of daughter isotopes Healing of fission tracks |
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Radiometric Age Dating
Memorable Dates (from Prothero & Dott, 2004) |
(Millions of year)
Meteorites 4,300-4,600 Moon Rocks 3,500-4,200 Pb ratio dating of Earth 4,600-4,700 Oldest known crustal 3,900-4,400 Beginning of Phanerozoic Eon 540 Paleozoic-Mesozoic boundary 250 Mesozoic-Cenozoic boundary 66 |
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Radiometric Age Dating
Half-life |
Mathematical formula for the rate of change of the number of parent atoms (-dN/dt) can be used to calculate the half-life from the number of breakdowns per second in a sample of the nuclide.
Half-life equals the time it takes for ½ of the radioactive parent to decay to a stable daughter product. |
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Relative Age Dating
worldwide |
Widespread unconformities extending across continents can be used to subdivide the sedimentary rock record
These regional unconformities represent large regressions, exposing large areas of the continents. First identified by Larry Sloss in the 1960s. |
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Beginnings of the Earth
[Chapter 6] Basic Principles |
Solar Nebula
Condensation Temperatures Planetesimals to Planetoids to Planets Differentiation of elements on Earth Atmosphere & Ocean Evolution |
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Table 6.2: Possible time scale for Early Solar System Evolution during the First 1 billion years, beginning with contraction of an interstellar cloud. (Time zero is assumed to have been about 5 billion years ago). From Prothero & Dott (2004).
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0-Spinning nebula of dust, gas, and ices
10,000-Protosun separating from nebular cloud 100,000-Asteroid-sized planetesimals accreting 1,000,000-Inner four terrestrial planets 1,000,000,000-Last planetesimals swept up and large craters formed by the last major impacts; great volumes of basalt erupted in lowlands of terrestrial planets. |
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Table 6.5: Proposed Stages for the early evolution of the Earth. From Prothero & Dott (2004).
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4.7-4.5:The solar nebula condensed, and the sun and protoplanets began to form; earth’s core condenses from the mantle
4.5-4.4: Intense heating from gravitational contraction, radioactive decay, and meteorite bombardment; loss of gases from interior of the Earth; H & He escape the Earth 4.4-4.0: First crustal rocks formed, including silicic crustal materials, although they were largely remelted and recycled; meteorite bombardment reached a climax; liquid water on the surface of Earth 3.9:Meteorite bombardment declined abruptly as loose nebular debris has been swept up into planets and the sun; first stable continental crust. 3.8:Rapid build-up of silicic crustal material to form protocontinents 3.6-3.5:Stable but thin continental crust; first fossil evidence of cyanobacteria and stromatolites |
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Atmosphere & Oceans
Two hypothesis on the origin of Earth’s atmosphere & oceans: |
Outgassing and photochemical
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Outgassing
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– water vapor, carbon dioxide, sulfur dioxide were outgassed during volcanic eruptions. These gases accumulated in the atmosphere.
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Photochemical
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– In the very early stages of Earth’s history, the atmosphere was similar to that of Jupiter and the other gas giants. Gases changed by photochemical reactions.
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Atmosphere & Oceans
Photochemical Reactions |
2H2O + uv-light = 2H2 (removed) + O2
CH4 + 2O2 = CO2 + 2H2O 4NH3 + 3O2 = 2N2 + 6H2O What’s the source of the oxygen in Earth’s atmosphere? |
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Cryptozoic History
[Chapters 8] Basic Principles: |
Geologic provinces & continental accretion
Archean Greenstone & Gneiss Belts Continental Rifting in North America Build-up of oxygen in the atmosphere Snowball Earth |
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Archean (4.6 to 2.5 b.y.)
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1. Greenstone belts
2. Gneiss belts |
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1. Greenstone belts
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– belts of mafic intrusive rocks such as basalt and komatiite associated with heterogeneous immature clastic sediments rich in feldspar and volcanic rock fragments.
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2. Gneiss belts
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– varied metamorphic rocks representing small continents. Limited development of continental crust before 2.5 billion years due to the increased radioactive heat of Earth’s interior.
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Cryptozoic of North America
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Transition of Continental Crust
Keweenawan Rifting Grenville Orogeny |
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Transition of Continental Crust
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– older greenstone belts are intruded by more felsic-rich materials; Algoman orogeny in North America (~2.5 Ga).
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Keweenawan Rifting
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- rifting event in the central part of North America; failed event; 1.3 to 1.1 Ga
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Grenville Orogeny
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– mountain building episode in eastern North America, 1.2 to 0.9 Ga
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Uniformity – “Present is the key to understanding the past”
Evidence of water |
Ripples – flowing water on the continents
Turbidites – evidence of relief along continental margins Mudcracks – sediments exposed to the atmosphere |
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Uniformity – “Present is the key to understanding the past”
Evidence of atmosphere |
Cross-bedding
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Evolution of Weathering & Sandstone Composition
Textural & Compositional Maturity of Sediments |
Precambrian sandstones are compositionally and texturally immature.
Oxygen-limited atmosphere results in reduced weathering rates which produce compositionally immature sandstones Increased oxygen results in alteration of most minerals; results in sandstones rich in quartz |
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Cryptozoic Oceans & Atmospheres
Increasing levels of oxygen |
Early: Any original oxygen is quickly consumed by hydrogen & carbon:
2H2 + O2 = 2H2O (water) C + O2 = CO2 (carbon dioxide) Later: With increasing oxygen available from photosynthesis: 4Fe + 3O2 = 2Fe2O3 (hematite) Ca + S + 2O2 = CaSO4 (anhydrite) Ca + CO3 = CaCO3 (limestone) |
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Build-up of Oxygen in Earth’s Atmosphere
Banded Iron Formations |
Oxygen produced by photosynthetic algae & bacteria immediately reacts with reduced iron & silica in seawater
Precipitation of iron oxides & quartz in the oceans BIFs occur in rocks 3.5 to 1.8 billion years old. |
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Consequence of Oxygen-Rich Atmosphere - Glaciation
Late Proterozoic |
Extensive glacial deposits: diamictites (tillites) & pebbly mudrocks (dropstones)
Glacial deposits extended into tropical latitudes; “Snowball Earth” hypothesis; associated with Rodinia supercontinent Implications for Cambrian “explosion of life”? |
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Plate Tectonics
[Chapters 7] Basic Principles |
Ocean Floor Topography
Paleomagnetism of the Ocean Floor Age of the Ocean Floor Plate Boundaries Divergent, Convergent, & Transform Margins |
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Subsidence & Sedimentary Basins
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Subsidence – the formation of space allowing for thick accumulations of sedimentary strata Subsidence mechanisms:
Subduction Cooling Subsidence Crustal thinning Sediment loading Thrust loading |
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basin type: trench
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fine sediments overlying ocean floor basalts deposited in deep marine environments
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basin type: forearc
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heterogeneous gravels, sands, muds derived from erosion of volcanic, metamorphic, and granitic rocks of the adjacent orogenic belt, deposited in continental to marine enverionments
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Basin type: foreland
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heterogeneous gravels, sands, muds derived from the orogenic belt and shed onto the continental craton; coal bearing, deposited in mostly river and deltaic environments
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Basin type: intracratonic
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homogenous quartz rich sands and limestones, but may include muds, evaporites, or coal at certain times, deposited in mostly shallow marine with some deltaic environments
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basin type: Passive margin
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quartz rich sands and limestones passing seaward to muds, deposited in shallow shelf to deep marine environments
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basin type: rift or aulocogen
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earliest rocks volcanic overlain by thick gravel and sand; younger rocks may include evaporites and limestones deposited in rivers and lakes changing to shallow marine
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