Earth, Atmospheres and the Moon - Key Vocabulary

Vocabulary flashcards covering the formation of Earth, atmospheric evolution and layers, plate tectonics, and Lunar dynamics based on the lecture material.

Accretion

The process during early planet formation where lumps of rock pull in surrounding material via gravitational attraction, growing into larger bodies until a planet is formed.

Differentiation

The process approximately $4.6$\,Gya in which elements settling under gravity cause denser materials (like iron) to sink toward the core while lighter silicates float to the outside.

Giant Impact Hypothesis (The Big Splat)

The theory that Earth underwent a glancing collision with a Mars-sized planetesimal, vaporizing the impactor and ejecting Earth's outer mantle and crust to form the Moon.

Subduction

The process where older, cooler, and denser crust sinks into the underlying mantle, dragging attached sections of crust down with it.

Albedo

The fraction of solar radiation reflected by a body's surface, which increased during supercontinent eras due to polar ice caps and interior desertification, causing global cooling.

Outgassing

The release of trapped gases from Earth's interior through volcanic activity, which formed Earth's early atmosphere.

Banded Iron Formations (BIFs)

Sedimentary rock structures featuring alternating layers of grey un-oxidised iron and red oxidised iron, recording the emergence of photosynthetic cyanobacteria and seasonal oxygen release.

Homosphere

The layer of Earth's atmosphere below $80\,\text{km}$ altitude where gases are thoroughly mixed by convection and turbulence, consisting primarily of nitrogen, oxygen, and carbon dioxide.

Troposphere

The lowest atmospheric layer ($0-20\,\text{km}$) containing $80\%$ of total air mass and almost all water vapor, where all weather phenomena take place.

Stratosphere

The atmospheric layer extending from $10\,\text{km}$ to $50\,\text{km}$ containing the highest ozone concentration at $35\,\text{km}$ and experiencing warming temperatures above $30\,\text{km}$.

Mesosphere

The atmospheric layer from $50\,\text{km}$ to $80\,\text{km}$ where temperatures drop to around $-95\,^\circ\text{C}$ at the mesopause boundary.

Thermosphere

The atmospheric layer between $80\,\text{km}$ and $300\,\text{km}$ altitude where particles absorbing UV and X-ray photons reach temperatures around $1000\,^\circ\text{C}$ at $350\,\text{km}$.

Exosphere

The outermost region of the atmosphere ($300-10000\,\text{km}$) containing sparse molecular traces before merging into space.

Tidal Locking (Synchronous Rotation)

A condition caused by gravitational tidal friction slowing a body's spin until one side permanently faces the primary body it orbits.

Obliquity

The tilt angle of a planet's rotational spin axis relative to the line perpendicular to its orbital plane ($23.5^\circ$ for Earth).

Precession

The slow, circular tracing of Earth's rotational axis in space over a $26,000\text{-year}$ cycle, caused by gravitational forces pulling on its equatorial bulge.

Smoothed Particle Hydrodynamics (SPH)

A computational technique developed by Monash astrophysicists used to model high-velocity giant impact collisions between planetary bodies.

Mechanical Layers

The classification of Earth's interior into distinct physical layers based on physical properties, comprising the lithosphere, mesosphere, outer core, and inner core.