Pangaea - the name of the single landmass that began to break apart 200 million years ago and gave rise to today’s continents

Fossil - the preserved remains or traces of an organism that lived in the past

Plate- a section of the lithosphere that slowly moves over the asthenosphere, carrying pieces of continental and oceanic crust

Fault -a break in Earth’s crust along which rocks move

Compression - Stress that squeezes rock until it folds or breaks

Earthquake - The shaking that results from the movement of rock beneath the Earth’s surface

Epicenter - The point on Earth’s surface directly above an earthquake’s focus

Focus - The point beneath Earth’s surface where rock first breaks under stress and causes an earthquake

P wave - A type of seismic wave that compresses and expands the ground

S wave - A type of seismic wave in which the shaking is perpendicular to the direction of the wave

Seismograph - A device that records ground movements caused by seismic waves as they move through Earth

Shearing - Stress that pushes masses of rock in opposite directions, in a sideways movement

Stress - A force that acts on a rock to change its shape or volume

Surface wave - A type of seismic wave that forms when P waves and S waves reach Earth’s surface

Tension - Stress that stretches rock so that it becomes thinner in the middle

Abrasion - the grinding away of rock by other rock particles carried in water, ice, or wind

Bedrock - rock that makes up Earth’s crust; also the solid rock layer beneath the soil

Erosion - the process by which water, ice, wind, or gravity moves weathered particles of rock and soil

Humus - dark-colored organic material in the soil

Loam - rich, fertile soil that is made up of about equal parts of clay, sand, and silt

Oxidation - a chemical change in which a substance combines with oxygen, as when iron oxidizes, forming rust

Permeable - characteristic of a material that contains connected air spaces, or pores, that water can seep through easily

Soil - the loose, weathered material on Earth’s surface in which plants can grow

Weathering - the chemical and mechanical processes that break down rock and other substances

Deposition - the process in which sediment is laid down in new locations

Erosion - the process by which water, ice, wind, or gravity moves weathered particles of rock and soil

Runoff - water that flows over the ground surface rather than soaking into the ground

Sediment- small, solid pieces of material that come from rocks or the remains of organisms; earth materials deposited by erosion

Geologic time scale - a record of the geologic events and life forms in Earth’s history

Era - one of the three long units of geologic time between the Precambrian and the present

Period - one of the units of geologic time into which geologists divide eras