geolgy

Continental Drift Hypothesis

Proposed by Alfred Wegener, the idea that landmasses move over geological time, supported by evidence like matching coastlines, fossil distributions, coal deposits, glacial formations, and mountain range distributions.

Continental Fit Boundary

The true boundaries where South America and Africa match up across the Atlantic Ocean, located $900\,m$ below sea level.

Seafloor Spreading

The process at oceanic ridges (like the Mid-Atlantic Ridge) where new oceanic crust is created, resulting in the oldest oceanic crust being located farthest from the ridge along continental coasts.

Lithosphere

The rigid outer layer of Earth made of continental crust, oceanic crust, and the uppermost mantle, which floats on the asthenosphere.

Asthenosphere

A solid layer of the upper mantle below the lithosphere that is capable of flowing under high temperature and pressure.

Earth's Core

The innermost region of the planet, divided into a liquid outer section and a solid inner section.

Subduction Zone

A convergent plate boundary where an oceanic plate sinks beneath another plate because it is denser, generating deep earthquakes and chains of volcanic mountains.

Continental Rift Zone

A tectonic setting where landmasses pull apart, forming features like linear seas.

Transform Boundary

A tectonic plate boundary where plates slide side-to-side horizontally past one another, exemplified by the San Andreas Fault.

Continental-Continental Collision

A convergent boundary where two landmasses collide, forming mountain ranges like the Himalayas.

Hotspot

An area of upwelling mantle (mantle plume) not located at a plate boundary that produces volcanism and volcanic chains like Hawaii.

Active Margin

A coastal region near a tectonic plate boundary characterized by high earthquake and volcanic activity.

Mineral

A naturally occurring, inorganic solid with an ordered internal atomic structure and a definite chemical composition.

Mineral Formation Processes

The main pathways by which inorganic crystalline solids originate: precipitating from aqueous solutions, precipitating by organisms, or crystallizing from magma.

Cation

A positively charged ion formed when an atom loses one or more electrons.

Anion

A negatively charged ion formed when an atom gains one or more electrons.

Ionic Bonding

Chemical bonding characterized by the transfer of electrons between atoms.

Covalent Bonding

Chemical bonding characterized by the sharing of electrons between atoms.

Metallic Bonding

Chemical bonding where valence electrons move freely among a lattice of metal atoms.

Van der Waals Bonding

Weak chemical bonds that hold together carbon sheets in graphite, whereas strong covalent bonds hold carbon together in diamond.

Oxygen and Silicon

The two most abundant elements in Earth's crust, together comprising about $84\%$ of crustal atoms.

Silica Tetrahedron

The fundamental building block of silicate minerals, composed of $1$ silicon atom surrounded by $4$ oxygen atoms.

Quartz

A light-colored silicate mineral composed of pure silica ($SiO_2$) with a 3-D framework tetrahedra arrangement.

Mafic Silicates

Dark-colored silicate minerals (black and green) rich in iron and magnesium.

Felsic Silicates

Light-colored silicate minerals (like quartz and feldspar) rich in silica and aluminum.

Native Elements

Minerals that consist of a single element uncombined with other elements.

Cleavage and Fracture

Physical properties of minerals describing how they break along planes of weakness versus breaking irregularly.

Igneous Rock

Rock formed from the cooling and solidification of molten rock (magma inside the Earth or lava on the surface).

Plutonic (Intrusive) Rock

Rock formed deep below Earth's surface from slow-cooling magma, resulting in coarse-grained (phaneritic) textures.

Volcanic (Extrusive) Rock

Rock formed on or near Earth's surface from fast-cooling lava, resulting in fine-grained (aphanitic) or glassy textures.

Vesicular Texture

An igneous rock texture containing holes formed by gas bubbles trapped in cooling lava.

Porphyritic Texture

An igneous rock texture with large crystals (phenocrysts) embedded in a fine-grained groundmass, caused by a two-stage cooling history.

Geothermal Gradient

The rate at which temperature increases with depth inside the Earth.

Xenolith

A piece of surrounding country rock that becomes enclosed within a magma body without melting.

Assimilation

The process where rising magma melts and incorporates surrounding country rock, altering the magma's chemical composition.

Fractional Crystallization

The removal and segregation of early-formed crystals from magma, causing the remaining liquid magma to become progressively more silica-rich (felsic).

Magma Generation Mechanisms

The processes by which molten rock forms in the subsurface: decompression melting (reducing pressure), flux melting (adding volatiles), or heat transfer from upwelling mantle.

Bowen's Reaction Series

A model predicting the order in which minerals crystallize from cooling magma, starting with olivine at high temperatures and ending with quartz at low temperatures.

Dike

A sheet-like igneous intrusion that cuts vertically or steeply across existing rock layers.

Sill

A sheet-like igneous intrusion that injects horizontally between pre-existing rock layers.

Mauna Loa

The largest volcano on Earth, categorized as a shield volcano built from low-viscosity effusive eruptions.

Viscosity

A fluid's resistance to flow; silica-rich magmas have higher values, trapping gases and driving explosive volcanic eruptions.

Lahar

A destructive volcanic hazard consisting of a mudflow of water, ash, and rock debris.

Pyroclastic Flow

A fast-moving, high-temperature cloud of ash, rock fragments, and gas rushing down a volcano's slopes during an explosive eruption.