CEE 437 Lecture 2History of Geology

Geologic Time Plate Tectonics

Thomas Doe

Geology — Brief History

Origins in late 18th and early 19th CenturiesCatastrophism and Uniformitarianism

Age of EarthUniformity of Processes

Plate Tectonics Revolution (1950’s to 1980’s)Neo-Catastrophism

Siccar Point Unconformity

Rock Cycle

Metamorphic Rocks

Sedimentary Rocks

Igneous Rocks

Sediments

Lithification

Magma

Weathering, Erosion

Burial, metamorphism, recrystallization

Melting

Crystallization at depth or extrusion at surface

Burial, metamorphism, recrystallization

Relative Time

Principle of SuperpositionFossil EvidenceCross Cutting RelationshipsUnconformitiesAlterationFracture Termination

Geologic Time Scale — Eras

Precambrian — Minimal fossil recordEra, Period, EpochBased on major changes — extinctions, mountain building events

Paleozoic (Old Life) —Brachiopods, Trilobites, Fish

Periods based on English GeologyCambrian for Latin WalesOrdovician and Silurian for ancient Welsh TribesDevonian for DevonCarboniferous for Coal Measures (also Mississippian and Pennsylvanian in US)Permian for Perm Basin in Ukraine

Mesozoic (Middle Life) —Ammonites, Dinosaurs

Triassic based on distinctive three-layer stratigraphy in southern GermanyJurassic based on Jura Mountains in France and SwitzerlandCretaceous (Latin for Chalk) based on chalk unit that forms Dover’s cliffs

Cenozoic (Recent Life) —Mammals, Modern marine fauna

(foraminifera)

Periods are Tertiary (before Ice Ages) and Quaternary (ice ages)Primary and secondary have been long replacesRocks of western Washington are primarily Tertiary and Quaternary in age

Age of the Earth

Kelvin and a basis in heat flow (set at 20 million years)Problem of fitting all of evolution in this timeRutherford and the introduction radioactive decayAdded a head source, pushed ages back to 4.5 billion years

Absolute Time

Basis on radiometric dating Common dating tools

14C, K-Ar, Rb-Sr,Uranium decay series

Development of Plate Tectonics

Evidence from ocean floor magnetism and agesEvidence from seismicityEvidence from cross-continent correlations of rocks

Global Seismicity

Benioff Zone

Seafloor Spreading — Sediment Ages

Sea-floor Spreading

Mantle convection driven

Evolution of Spreading Sea Floor — Atlantic Analog

Convergent Margins

Ocean to ContinentContinent to Continent

Convergent Margin - Continental

Subduction Zone – Island Arc

Evolution of Continents — North American Craton

North American Accretion