Geology Midterm

A fossil species that was geographically widespread, easily identifiable, and existed for a short, well-defined geological duration, making it ideal for stratigraphical correlation.

An unconformity where younger sedimentary rocks were deposited directly on top of eroded, exposed crystalline igneous or metamorphic basement rocks.

The boundary surface separating two distinct sedimentary rock beds, representing a pause or change in sediment deposition.

An unconformity where older rock layers are tilted or folded, eroded, and overlain by younger layers deposited at a different angle, often horizontally.

Igneous rocks and metamorphic rocks

Atoms of the same chemical element that possess the same number of protons but varying numbers of neutrons, resulting in different atomic mass numbers.

Permian Period (approx. 299 to 252 million years ago).

Sediment consists of loose, unlithified mineralock fragments or chemical precipitates; sedimentary rock consists of sediment that has undergone lithification (compaction and cementation).

Approximately 541 to 542 million years ago (marked by the widespread appearance of hard-shelled organism fossils).

Convective movement and fluid motion of liquid iron-nickel metal within the outer core.

Phosphorite

A naturally occurring, inorganic solid with a highly-ordered atomic structure and a definable chemical composition. (Mnemonic: 'N-S-O-C' for Naturally-occurring, Solid, Ordered-structure, Composition).

Earth's original surface rocks have been recycled or destroyed by plate tectonics, erosion, and metamorphism, whereas meteorites remain unaltered primitive solar system materials.

Peridotite

The ancient, stable geological interior core of a continental landmass.

Felsic melt

A biochemical variety of limestone formed from the microscopic calcium carbonate shells of planktonic organisms.

Blueschist facies metamorphism

Ash → Lapilli → Volcanic Bomb

Sedimentary layers accumulate in continuous sheets extending laterally in all directions until they thin out or abut against a basin boundary.

Angular unconformity

3 half-lives (1 → 1/2 → 1/4 → 1/8).

Paleozoic Era → Mesozoic Era → Cenozoic Era

Soil is rock and sediment that has been chemically altered by organic matter, rainwater, and living organisms over time.

The foundational geological principle formulated by James Hutton stating that physical processes operating today operated similarly in the geological past ("The present is the key to the past").

A rock formed when pre-existing parent rock undergoes solid-state recrystallization due to changes in pressure (P), temperature (T), or chemical fluids without melting completely.

Metamorphism resulting predominantly from intense directional shearing stress along fault zones, occurring under high pressure (P) and low temperature (T).

Chert (flint)

Science is a way of thinking much more than it is a body of knowledge" — a systematic approach to acquiring and evaluating knowledge through empirical evidence.

1. Air (Atmosphere) 2. Water (Hydrosphere) 3. Land (Geosphere/Lithosphere) 4. Life (Biosphere)

A dike cuts across existing rock layers; a sill intrudes parallel to existing layers.

Graded bedding

Flux melting (addition of water lowers the melting temperature of mantle rocks).

Marble

The Principle of Cross-Cutting Relationships (dike D intrudes and cuts across rock layers E, C, and B).

Sylvite (KCl)

If a geological feature (such as a fault or igneous intrusion) cuts across another rock unit, it must be younger than the unit it cuts.

A continuous sequence of strata distinct enough in rock type to be recognized and mapped across a broad geographical region.

An erosional surface or non-depositional gap separating parallel, horizontally oriented sedimentary rock strata.

A group of interconnected, interacting physical and biological components (spheres) operating together under physical laws as a unified whole.

Shale

Any rock fragment (xenolith or clast) enclosed within another rock must be older than the host rock that contains it.

In an undeformed sequence of sedimentary rocks, each layer is younger than the layer below it and older than the layer above it.

The alteration of a rock's chemical composition caused by hot, ion-rich hydrothermal fluids flushing through it.

Nature is not compartmentalized into university departments; investigating natural systems requires integration across ancillary fields like chemistry, physics, and biology.

Thermal contact metamorphism occurs where hot igneous magma bakes pre-existing host rock; the baked host rock must be older than the intruding magma.

Approximately 4.56 to 4.57 billion years (4,567 Ma), determined via radiometric dating of meteorites.

Decompression melting (melting triggered by a decrease in pressure as hot mantle material ascends without heat loss).

The concept of geological time spanning billions of years (4.56 billion years), vast scales that dwarf human historical time.

2 half-lives (1 → 1/2 → 1/4).

Fossilized organisms succeed one another vertically in sedimentary strata in a definite, recognizable chronologic order over deep time.

Sediment layers are originally deposited horizontally under the action of gravity; steeply tilted strata must have been deformed by later tectonic events.

Mesozoic Era (comprising Triassic, Jurassic, and Cretaceous periods from ~252 to 66 Ma).

The fixed duration of time required for exactly 50\% (one half) of a radioactive parent isotope to decay into stable daughter products.

Widespread metamorphism driven by simultaneous high pressure (P) and high temperature (T) during major tectonic mountain-building collisions (e.g., the Himalaya orogeny).

Carbonate rock (such as limestone or dolomite).

A rock formed through the cooling and solidification of molten rock material (magma or lava). (Mnemonic: 'Ignite' = formed from heat/melt).

The giant-impact hypothesis: a Mars-sized body struck early Earth, and the debris eventually formed the Moon.

Radiocarbon has a short half-life (5,730 years) and can only date organic materials younger than about 50,000 to 70,000 years.

1. Naturally occurring 2. Solid state 3. Highly-ordered internal atomic structure 4. Definable chemical composition