geo 2

Ophiolites

Sections of oceanic crust and upper mantle that have been uplifted onto continental crust.

Wegener’s contributions to plate tectonics

Proposed continental drift theory; suggested continents move over time; used evidence like fossil distribution, rock types, and fit of continents.

Hess’ contributions to plate tectonics

Proposed seafloor spreading; suggested new oceanic crust forms at mid-ocean ridges and moves outward; key in modern plate tectonics.

Evidence supporting Wegener and Hess

Fossil correlation, matching rock types, paleoclimatic evidence, mid-ocean ridges, magnetic striping of seafloor, ages of oceanic crust.

Half-lives and calculating ages

Use the formula: N=N0(1/2)t/TN = N_0 (1/2)^{t/T}N=N0​(1/2)t/T to find remaining parent isotope; solve for time (t) using known half-life (T).

Dollo’s Law

Evolution is irreversible; once a complex structure is lost, it cannot re-evolve in the same form.

Transgressive facies stratigraphy

Sediments deposited as sea level rises; deeper-water facies overlie shallower-water facies.

Regressive facies stratigraphy

Sediments deposited as sea level falls; shallower-water facies overlie deeper-water facies.

Index fossils

Fossils that are widespread, abundant, and limited to a short geologic time interval; used for dating rocks.

Natural selection

Process where individuals with advantageous traits survive and reproduce more, passing traits to next generation.

Evolutionary radiation

Rapid diversification of a group of organisms into many forms filling different ecological niches.

Hot spots

Areas where plumes of hot mantle material rise to the surface, creating volcanoes independent of plate boundaries.

Subduction

Process where one tectonic plate moves under another and sinks into the mantle; associated with trenches and volcanic arcs.

Oxygen isotopes & oceans/glaciers

Ratio of O18/O16O^{18}/O^{16}O18/O16 in shells indicates past temperatures and ice volume; higher O18O^{18}O18 = more ice, cooler oceans.

Paleozoic atmospheric events

Examples: rise of oxygen in atmosphere (Late Ordovician), mass extinctions affecting air composition.

Rock cycle (no blue boxes)

Process showing how igneous, sedimentary, and metamorphic rocks form and transform through melting, cooling, erosion, deposition, and metamorphism.

Time scale (missing Precambrian/Paleozoic)

Know the sequence of geologic periods and approximate relative ages; use word bank to fill missing eras.

Walther’s Law

Vertical succession of facies reflects lateral changes in environment; transgressive/regressive sequences follow this principle.

Subduction zone (map view)

Map shows trench, volcanic arc, and overriding/descending plates; identify direction of subduction.

Subduction zone (cross-section)

Cross-section shows descending slab, mantle wedge, trench, and volcanic arc; explain process.

Cross-cutting relationships

Features that cut across others (faults, intrusions) are younger than what they cut through; principle used in relative dating.