Formation of the Earth & Plate Tectonics – Key Vocabulary

Vocabulary flashcards covering cosmological origins, Earth’s formation and differentiation, early geodynamic theories, continental drift evidence, and modern plate tectonics with major and secondary plates.

Big Bang Theory

Explains that the universe began ~13.8 billion years ago from an infinitely hot, dense singularity that expanded to create space, time, and matter.

Singularity (Cosmology)

An infinitely dense, hot point from which the Big Bang expansion began.

Nebular Hypothesis

Model stating the Solar System formed 4.6 billion years ago from the gravitational collapse of a giant molecular cloud, producing the Sun and a protoplanetary disk.

Solar Nebula

The rotating cloud of gas and dust left over from the Sun’s formation in which planetesimals and ultimately the planets formed.

Planetesimal

Kilometre-scale solid bodies formed by dust collision and sticking; building blocks of planets.

Accretion (Planetary)

Growth of a planetary body by the gradual accumulation of planetesimals and smaller particles.

Hadean Eon

Earliest geologic eon (starting ~4.6 Ga) marked by intense bombardment and a newly solidifying crust.

Differentiation (Planetary)

Process by which a molten planet separates into layers of different density, forming core, mantle, and crust.

Earth’s Core

Dense metallic inner region (solid inner core + liquid outer core) composed chiefly of iron and nickel; source of the magnetic field.

Mantle

Thick silicate layer above the core; convection within it drives plate tectonics.

Crust

Earth’s outermost solid layer, divided into continental and oceanic types where most surface geology occurs.

Contracting Earth Theory

Early 20th-century idea that Earth cooled and shrank, causing the crust to buckle into mountains and ocean basins (like a drying grape).

Isostasy

Concept that Earth’s lithosphere floats in gravitational equilibrium on the ductile asthenosphere, balancing mass differences.

Continental Drift

Hypothesis that continents move horizontally over geologic time relative to each other and ocean basins.

Alfred Wegener

German meteorologist who proposed continental drift and the supercontinent Pangea in 1912.

Pangea

Wegener’s proposed single supercontinent that existed until the Triassic, later fragmenting into present continents.

Fossil Correlation

Evidence for continental drift: identical fossils (e.g., Mesosaurus, Glossopteris) found on continents now separated by oceans.

Continental Fit

Matching coastlines (especially South America–Africa) supporting past continental connection.

Paleoclimate Evidence

Past climate indicators (e.g., glacial deposits, coal beds) aligning when continents are reassembled, backing drift theory.

Plate Tectonics Theory

Modern framework stating Earth’s lithosphere is broken into moving plates whose interactions cause seismic and volcanic activity.

Lithosphere

Rigid outer shell comprising crust plus uppermost mantle; broken into tectonic plates.

Primary (Major) Plates

Seven largest crustal plates: Pacific, North American, Eurasian, African, Antarctic, Indo-Australian, South American.

Secondary Plates

Intermediate-sized plates such as Arabian, Caribbean, Cocos, Indian, Juan de Fuca, Philippine Sea, Scotia, and Nazca.

Pacific Plate

Largest tectonic plate underlying the Pacific Ocean; hosts the Ring of Fire and Hawaiian hotspot.

North American Plate

Plate including North America, part of the Atlantic, Greenland, and parts of Siberia and Japan; contains a 4 Ga craton.

Eurasian Plate

Plate spanning Europe and most of Asia; diverges from North America at the Mid-Atlantic Ridge and splits Iceland.

African Plate

Plate containing Africa and adjacent Atlantic seafloor; rifting in the east is creating the Somali Plate.

Antarctic Plate

Plate encompassing Antarctica and surrounding oceans; separated from Gondwana ~100 Ma ago, moves ~1 cm/yr.

Indo-Australian Plate

Composite plate of Indian and Australian sections; once part of Gondwana, converges with the Pacific Plate to the NE.

South American Plate

Plate with South America and adjoining Atlantic floor; converges with the Nazca Plate forming the Andes.

Nazca Plate

Young oceanic plate subducting beneath South America along the Peru–Chile Trench, driving Andean orogeny.

Juan de Fuca Plate

Small oceanic plate off the Pacific NW of North America; site of Cascadia subduction zone.

Andean Orogeny

Mountain-building event along western South America caused by Nazca Plate subduction.

Ring of Fire

Zone of frequent earthquakes and volcanoes encircling the Pacific Plate’s boundaries.

Mid-Ocean Ridge

Elevated, volcanic divergent boundary where new oceanic crust forms (e.g., Mid-Atlantic Ridge).

Convergent Boundary

Plate boundary where plates move toward each other, often causing subduction or continental collision.

Divergent Boundary

Plate boundary where plates move apart, creating new lithosphere at mid-ocean ridges or rift valleys.

Transform Boundary

Plate boundary where plates slide horizontally past each other, exemplified by the San Andreas Fault.

Continental Plate

Thick, buoyant lithospheric plate composed mainly of granitic rocks.

Oceanic Plate

Thinner, denser lithospheric plate composed chiefly of basalt and gabbro.