GEOS 212 Lecture 2: Plate Tectonics and Ocean Crust

Vocabulary flashcards covering key definitions from GEOS 212 Lecture 2 Part 1 and Part 2 on plate tectonics, geochemical and physical layers of Earth, crustal composition, plate boundaries, spreading centers, hydrothermal vents, and ocean formation stages.

Plate

A large, rigid piece of Earth's lithosphere that moves over time.

Lithosphere

The rigid outer shell of Earth consisting of the crust and uppermost mantle.

Asthenosphere

A weaker, ductile part of the upper mantle that flows slowly over long time scales and allows tectonic plates to move.

Divergent boundary

A boundary where tectonic plates move apart from each other and new oceanic crust is created.

Convergent boundary

A boundary where tectonic plates move toward each other and one plate is subducted and destroyed in the mantle.

Transform boundary

A boundary where tectonic plates slide horizontally past each other, with crust neither created nor destroyed.

Spreading center

A mid-ocean ridge where magma rises from the mantle and new oceanic crust forms as plates pull apart.

Geochemical layers

Earth's internal layering system defined by composition (what Earth is made of), consisting of the crust, mantle, and core.

Physical layers

Earth's internal layering system defined by mechanical behavior, including the lithosphere, asthenosphere, lower mantle, outer core, and inner core.

Continental crust

Thicker ($30\text{--}35\text{ km}$), less dense ($2.7\text{ kg/L}$) crustal rock composed mainly of felsic granite.

Oceanic crust

Thinner ($7\text{ km}$), denser ($3.0\text{ kg/L}$) crustal rock composed mainly of mafic basalt.

Granite

Light-colored, felsic rock rich in silica with a density of $2.7\text{ kg/L}$ that primarily composes continental crust.

Basalt

Darker, mafic rock rich in iron and magnesium with a density of $3.0\text{ kg/L}$ that primarily composes oceanic crust.

Outer core

The physical layer composed of liquid iron-nickel located between $2{,}900\text{ km}$ and $5{,}150\text{ km}$ depth that flows to generate Earth's magnetic field.

Inner core

The physical layer composed of solid iron-nickel located from $5{,}150\text{ km}$ to $6{,}371\text{ km}$ depth, held solid by extreme pressure.

Hydrothermal vent

A deep-ocean hot spring along mid-ocean ridges where hot, mineral-rich fluid ($400^\text{o}\text{C}$) exits the seafloor.

Chemosynthesis

The process by which bacteria at hydrothermal vents produce food using chemical energy from molecules like hydrogen sulfide ($\text{H}_2\text{S}$) instead of sunlight.

Tube worms

Hydrothermal vent organisms that grow up to $2\text{ m}$ long, host symbiotic chemosynthetic bacteria, and appear bright red due to hemoglobin.

Pompeii worms

Heat-tolerant hydrothermal vent animals that can survive in fluids up to $80^\text{o}\text{C}$.

Mid-Atlantic Ridge

A global mid-ocean ridge with a slow spreading rate ($2\text{--}4\text{ cm/yr}$) extending $16{,}000\text{ km}$ from the Arctic to the Southern Ocean.

East Pacific Rise

A fast-spreading center in the eastern Pacific Ocean with a spreading rate of $15\text{--}17\text{ cm/yr}$.

East African Rift

A continental rift system (triple junction) where the African Plate is actively splitting into the Nubian and Somali plates.

Rift

The initial stretching and breaking of continental crust as tectonic plates begin to diverge.

Rift valley

A down-dropped valley formed by normal faults in a rifting region on land.

Linear sea

A narrow, elongated body of water, such as the Red Sea or Gulf of California, formed when seawater floods a rift valley.

Mature ocean

A wide, fully developed ocean basin with oceanic crust and an active mid-ocean ridge, such as the Atlantic Ocean.