NCEA Level 2 Earth and Space Science flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Lithospheric plate

A rigid slab of Earth's crust and uppermost mantle that moves over the weaker asthenosphere, driven by mantle convection and slab pull, at rates of a few centimetres per year.

Divergent plate boundary

A boundary where plates move apart, such as a mid-ocean ridge or continental rift, allowing magma to rise and form new crust; characterised by shallow earthquakes and volcanism.

Subduction zone

A convergent boundary where one denser plate sinks beneath another into the mantle, producing deep earthquakes, volcanic arcs, ocean trenches and mountain belts such as the Andes.

Transform boundary

A boundary where two plates slide horizontally past each other without creating or destroying crust, producing shallow earthquakes; New Zealand's Alpine Fault is an example.

Seafloor spreading

The process where new oceanic crust forms at mid-ocean ridges and moves away on both sides; evidence includes matching magnetic striping, youngest crust at ridges and symmetric age patterns.

Superposition principle

In an undisturbed sequence of sedimentary rock layers, the lowest layer is the oldest and the highest is youngest, establishing relative age order without radiometric dating.

Half-life

The time taken for half the radioactive parent atoms in a sample to decay; after one half-life 50% remains, after two 25%, after three 12.5%.

Rock cycle

The continuous transformation among igneous, sedimentary and metamorphic rocks through melting, cooling, weathering, deposition, compaction, heat and pressure, without any fixed start or end.

S-wave shadow zone

A region where secondary seismic waves are not detected, showing that S-waves cannot travel through liquid; this provides evidence that Earth's outer core is liquid.

Weathering vs erosion

Weathering breaks down rock in place by physical, chemical or biological processes; erosion then transports the broken material by water, wind, ice or gravity to be deposited elsewhere.

Axial tilt and seasons

Earth's axis is tilted 23.5° from the perpendicular to its orbit, so each hemisphere receives more direct sunlight for half the year, producing opposite seasons without changing distance from the Sun.

Synodic month

The time between successive identical Moon phases, about 29.5 days, longer than the 27.3-day sidereal orbit because Earth also moves around the Sun during that period.

Solar eclipse

An alignment where the Moon passes between the Sun and Earth at new moon, casting a shadow on Earth; rare because the Moon's orbit is tilted about 5° from Earth's orbital plane.

Lunar eclipse

An alignment where Earth passes between the Sun and Moon at full moon, so Earth's shadow falls on the Moon; visible from the night side of Earth and can last over an hour.

Spring tide

An unusually large tidal range occurring at new and full moon, when the Sun and Moon pull in line so their gravitational effects add together, producing highest highs and lowest lows.

Neap tide

A small tidal range occurring at first and last quarter moon, when the Sun and Moon pull at right angles so their tidal effects partly cancel.

Kepler's third law

The square of a planet's orbital period is proportional to the cube of its semi-major axis (P² ∝ a³), linking orbital distance to orbital speed and period.

Hertzsprung-Russell diagram

A graph plotting star luminosity against surface temperature or spectral class; most stars lie on the main sequence, with giants, supergiants and white dwarfs in distinct regions.

Redshift

The stretching of light from receding objects toward longer wavelengths; greater redshift of distant galaxies indicates faster recession, supporting an expanding universe.

Light-year

The distance light travels in one vacuum year, about 9.46 × 10¹² km; used for interstellar and intergalactic distances because conventional units become unwieldy.

Main sequence star

A star fusing hydrogen into helium in its core, in stable equilibrium between gravity and radiation pressure; the Sun is a main-sequence star about halfway through its life.

Carbon cycle

The movement of carbon among the atmosphere, oceans, biosphere and rocks via photosynthesis, respiration, combustion, dissolving and weathering; human fossil-fuel burning adds carbon to the atmosphere.

Greenhouse effect

Atmospheric gases absorb outgoing infrared radiation and re-emit it in all directions, warming the surface and lower atmosphere; it is natural but enhanced by rising CO₂ and methane.

Albedo

The fraction of incoming solar radiation reflected by a surface; fresh snow and ice are high albedo, oceans and dark rock low, so changing ice cover alters Earth's energy balance.

Positive feedback

A process where a change amplifies itself, such as melting ice lowering albedo and causing more warming; positive feedbacks can accelerate climate change.

Negative feedback

A process that counteracts a change and stabilises the system, such as increased cloud cover reflecting sunlight; negative feedbacks tend to dampen climate change.

Thermohaline circulation

A global deep-ocean circulation driven by differences in temperature and salinity, carrying warm surface water poleward and cold dense water to the deep ocean, redistributing heat.

Ocean acidification

The decrease in ocean pH as seawater absorbs atmospheric CO₂, forming carbonic acid; it harms shell-forming organisms such as corals and shellfish.

Climate proxy

A preserved record such as ice cores, tree rings, corals or sediments used to reconstruct past temperature and atmospheric composition when direct measurements do not exist.

Mitigation

Action that reduces the causes of climate change, such as replacing fossil fuels with renewable energy, improving efficiency, or planting forests to absorb carbon dioxide.

Adaptation

Action that reduces vulnerability to climate impacts, such as building sea walls, developing drought-tolerant crops, or adjusting flood planning and land use.

Earth's energy balance

The balance between incoming solar radiation and outgoing reflected plus infrared radiation; when the balance shifts, the global mean temperature changes until equilibrium is restored.