GEOL 106 Midterm Study Materials Flashcards

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Uniformitarianism

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The idea that geological processes operating today also operated in the past, allowing modern observations to be used to interpret ancient rocks. It emphasizes gradual processes but does not exclude rare catastrophic events that leave a rock record.

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Principle of Actualism

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A refinement of uniformitarianism stating natural laws are constant through time, though rates and intensities of processes may differ. Actualism allows for both slow processes and episodic catastrophic events in Earth history.

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End-Permian Extinction

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A mass extinction event around 252 Ma that eliminated roughly 81% of marine and 70% of terrestrial species. It is linked to Siberian flood basalt volcanism, massive CO2 release, and a global temperature rise estimated at ~8°C.

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Lord Kelvin's Age Estimate

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A 19th-century thermodynamic calculation that estimated Earth's age at ~98 million years by modeling cooling of a molten Earth. It was incorrect because it ignored internal heat generation and convective heat transfer in Earth's interior.

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Arthur Holmes

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A geologist who pioneered the use of radioactive decay for dating rocks, laying groundwork for modern geochronology. Holmes demonstrated that radiogenic isotopes provide numerical ages far older than Kelvin's estimates.

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Radiogenic Isotopes

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Isotopes that decay spontaneously into daughter isotopes at a known rate, characterized by a half-life. By measuring parent:daughter ratios in minerals, geologists can calculate the time since the mineral closed to isotopic exchange.

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Acasta Gneiss

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A metamorphic rock in Canada dated to about 4.031 billion years, currently recognized as one of Earth's oldest known rocks. It provides evidence for early continental crust formation in the Hadean/early Archean.

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Detrital Zircon Grains

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Zircon mineral grains eroded from ancient rocks and preserved in younger sediments; the oldest known are ~4.36 billion years old. They are valuable because zircon resists weathering and can retain U-Pb ages through multiple cycles.

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Stratigraphy

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The study of rock layers (strata) and their relationships, used to interpret the sequence and relative timing of geological events. It pairs with numerical geochronology to reconstruct Earth's history.

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Fossils vs Subfossils

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Fossils are remains or traces of ancient life older than ~11,700 years, whereas subfossils are younger remains that have not fully lithified. Preservation is biased toward marine environments and specific conditions of burial and diagenesis.

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Taphonomy

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The study of processes that govern an organism's transition from death to fossilization, including decay, transport, burial, and chemical alteration. Taphonomy explains biases in the fossil record and modes of preservation.

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Hadean Eon

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The earliest interval of Earth's history characterized by a hot, volatile surface, frequent impacts, and the formation of the primitive crust and atmosphere. It predates abundant rock records and transitions into the Archean.

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Magnetic Field Origin

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Earth's magnetic field is generated by convection of molten iron in the outer core (the geodynamo). It shields the surface from solar wind and its past behavior is recorded by remanent magnetization in rocks.

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Milankovitch Cycles

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Orbital variations—eccentricity, obliquity, and precession—that change Earth's insolation patterns on timescales of tens to hundreds of thousands of years. They drive long-term climate cycles such as glacial–interglacial periods.

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Great Oxygenation Event (GOE)

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A major rise in atmospheric oxygen around 2.4–2.0 Ga driven by biological activity (e.g., photosynthetic microbes), which transformed redox conditions and enabled aerobic life. It left signatures like banded iron formations and oxidized minerals.

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Banded Iron Formations (BIFs)

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Layered sedimentary rocks of alternating iron-rich and silica-rich bands formed primarily in the Precambrian when oxygen produced by microbes oxidized dissolved iron. BIFs record changes in ocean chemistry and atmospheric oxygenation.

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Stromatolites

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Layered, laminated structures produced by microbial mats (often cyanobacteria) that trap and bind sediments; they are among the oldest macroscopic evidence of life. Stromatolites are important in studying early biospheric activity and oxygen production.

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Closure Temperature

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The temperature below which a mineral becomes a closed system for a particular isotopic decay chain, meaning daughter isotopes are retained. Closure temperature controls the age recorded by radiometric dating of that mineral.

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Komatiite

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An ultramafic volcanic rock common in the Archean produced by very high-temperature magmas; it is rare in modern volcanism. Komatiite indicates hotter mantle conditions in Earth's early history.

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Study Materials Overview

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Two primary sets are available: compressed lecture notes/slides and a midterm exam review file outlining topics to touch. Use the slides for factual detail and the review file to prioritize topics for the exam.

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Midterm Review Scope

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The review emphasizes Precambrian geology, radiometric dating, major extinction events, stratigraphy, and fossilization processes. Focus study sessions on geochronology methods, Milankovitch cycles, GOE, and key ancient rock examples.