Geology Test Terms

Let's all manifest an 'A'.

cementation

The gluing together of sediment by new mineral crystals

Cementation can cause sediment grains to stick together, forming sedimentary rock.

compaction

The squeezing of sediment by the weight of overlying layers

Compaction can cause sediment grains to stick together, forming sedimentary rock.

continental crust

Crust that lies beneath a continent

Continental crust is about 25–70 km thick and is less dense than oceanic crust.

continental drift

The movement of continents around the surface of Earth

Continental drift theory was proposed by Alfred Wegener in 1912 but was widely accepted only in the 1960s.

convergent boundary

A place where two tectonic plates move towards each other

At convergent boundaries, mountain ranges, ocean trenches and volcanoes can form.

crust

The outermost layer of Earth

The crust is made of solid rock and is 5–70 km thick. It is thickest underneath the continents.

divergent boundary

A place where two tectonic plates move away from each other

At divergent boundaries, rift valleys and mid-ocean ridges can form.

earthquake

The sudden shaking of Earth's surface

An earthquake is a natural hazard that occurs when two slabs of rock suddenly slip against each other.

erosion

The wearing away and removal of rock

Eroded sediment is transported by wind, water or ice.

fossil

The remains or traces of an ancient organism preserved in rock

Fossils provide information about how life evolved and how Earth's surface has changed.

geologist

A scientist who studies the Earth

Geology is the scientific study of the processes that change the Earth and their history.

hotspot

An unusually hot part of the mantle where volcanoes can form

At hotspots, magma can rise through the crust to form volcanoes, even away from plate boundaries.

igneous rock

Any rock formed by the cooling of magma or lava

The size of the crystals in an igneous rock indicates the speed at which it cooled.

inner core

The innermost layer of Earth

The inner core is a solid mixture of iron and nickel at extreme pressures and temperatures.

lava

Hot liquid rock located above the Earth's surface

When magma rises up from underground and flows on the surface it is called lava.

lithosphere

The rigid outer part of Earth, made of the crust and upper mantle

The lithosphere is divided into slow-moving tectonic plates.

magma

Hot liquid rock located below the Earth's surface

Magma can rise to the surface to form volcanoes.

mantle

The thickest layer of Earth, between the core and the crust

The mantle is made of solid and partially melted rock. It can flow over very long timescales.

melting

A change of state from solid to liquid

When rock is heated deep underground, it melts to form magma.

metamorphic rock

Any rock that has been changed by intense heat and pressure

Heat and pressure can change the types of minerals and the size and shape of the crystals.

mid-ocean ridge

An underwater mountain system where new oceanic crust forms

Mid-ocean ridges form at divergent boundaries. New oceanic crust is formed from cooling lava.

mineral

A natural substance usually found as crystals in rocks

Minerals are the building blocks of rocks. Quartz is a common rock-forming mineral.

mitigation

An action that decreases the harmfulness of an event

An emergency evacuation plan is one way to mitigate the damage from natural disasters.

natural disaster

An event in the natural world that causes death and destruction

Natural disasters cause injuries, deaths and damage to buildings, roads and towns.

natural hazard

An event in the natural world that endangers living things

Natural hazards include volcanic eruptions, earthquakes and tsunamis.

ocean trench

A deep valley in the ocean floor formed at a convergent boundary

Ocean trenches form where one plate subducts beneath another.

oceanic crust

Crust that lies beneath an ocean

Oceanic crust is about 5–10 km thick and is made up of basalt, a dense volcanic rock.

outer core

The layer of Earth that lies between the mantle and inner core

The outer core is a liquid mixture of iron and nickel. Its flow generates Earth's magnetic field.

parent rock

The original rock from which a metamorphic rock formed

Parent rocks may be sedimentary, igneous or metamorphic.

plate boundary

A border between two neighbouring tectonic plates

Tectonic plates interact at plate boundaries. This can cause earthquakes and volcanic eruptions.

pressure

The amount of force applied over a certain area

Pressure can be measured in the units pascal (Pa) and gigapascal (GPa).

relative dating

A method to determine if one rock layer is older or younger than another layer

In a sequence of sedimentary rocks, the lowest layer has the oldest relative age.

rift valley

A long depression formed when a continent is pulled apart

Rift valleys form at divergent boundaries in continental crust.

rock cycle

The set of changes that turn one rock type into another

Rocks can change between igneous, sedimentary and metamorphic types over millions of years.

seafloor spreading

The formation of new oceanic crust at a mid-ocean ridge

The discovery of seafloor spreading provided new evidence for continental drift theory.

sediment

Small rock fragments such as mud, sand or gravel

Sediments form when rock is exposed to weathering and erosion.

sedimentary rock

Any rock formed when sediment is compacted or cemented

Sedimentary rocks can also form from the remains of living things.

solidification

A change of state from liquid to solid

When magma cools quickly, it solidifies to form a rock with small crystals.

subduction

The sinking of one tectonic plate beneath another

Subduction occurs at convergent boundaries. Denser crust sinks beneath less dense crust.

supercontinent

A single landmass made of smaller continents joined together

There have been many supercontinents in Earth's history. Pangaea existed 280 million years ago.

tectonic plate

A section of the crust and upper mantle

The movements of tectonic plates cause most earthquakes and volcanic eruptions.

transform boundary

A place where two tectonic plates slide past each other

At transform boundaries, earthquakes often occur as pressure along faults is suddenly released.

tsunami

A large ocean wave caused by an earthquake or coastal landslide

A tsunami is a natural hazard that can cause widespread damage to coastal towns and cities.

volcanic eruption

A release of magma at the Earth's surface

The eruption of hot liquid rock forms natural hazards such as lava flows and ash clouds.

weathering

The breakdown of rocks into small grains or soil

Rocks at the surface are weathered by wind, flowing water, heat and other processes.