Key Terms

bar

a force of 100,000 Newtons acting on a surface area of 1 square meter; the average pressure of Earth’s atmosphere at sea level is 1.013 bars

basalt

igneous rock produced by the cooling of lava; makes up most of Earth’s oceanic crust and is found on other planets that have experienced extensive volcanic activity

convection

movement caused within a gas or liquid by the tendency of hotter, and therefore less dense material, to rise and colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat

core

the central part of the planet; consists of higher density material

crust

the outer layer of a terrestrial planet

fault

in geology, a crack or break in the crust of a planet along which slippage or movement can take place, accompanied by seismic activity

granite

a type of igneous silicate rock that makes up most of Earth’s continental crust

greenhouse effect

the blanketing (absorption) of infrared radiation near the surface of a planet—for example, by CO₂ in its atmosphere

greenhouse gas

a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range; on Earth, these atmospheric gases primarily include carbon dioxide, methane, and water vapor

igneous rock

rock produced by cooling from a molten state

magnetosphere

the region around a planet in which its intrinsic magnetic field dominates the interplanetary field carried by the solar wind; hence, the region within which charged particles can be trapped by the planetary magnetic field

mantle

the largest part of Earth’s interior; lies between the crust and the core

mass extinction

the sudden disappearance in the fossil record of a large number of species of life, to be replaced by fossils of new species in subsequent layers; mass extinctions are indicators of catastrophic changes in the environment, such as might be produced by a large impact on Earth

metamorphic rock

rock produced by physical and chemical alteration (without melting) under high temperature and pressure

ozone

(O₃) a heavy molecule of oxygen that contains three atoms rather than the more normal two

photosynthesis

a complex sequence of chemical reactions through which some living things can use sunlight to manufacture products that store energy (such as carbohydrates), releasing oxygen as one by-product

plate tectonics

the motion of segments or plates of the outer layer of a planet over the underlying mantle

primitive rock

rock that has not experienced great heat or pressure and therefore remains representative of the original condensed materials from the solar nebula

rift zone

in geology, a place where the crust is being torn apart by internal forces generally associated with the injection of new material from the mantle and with the slow separation of tectonic plates

sedimentary rock

rock formed by the deposition and cementing of fine grains of material, such as pieces of igneous rock or the shells of living things

seismic wave

a vibration that travels through the interior of Earth or any other object; on Earth, these are generally caused by earthquakes

stratosphere

the layer of Earth’s atmosphere above the troposphere and below the ionosphere

subduction

the sideways and downward movement of the edge of a plate of Earth’s crust into the mantle beneath another plate

troposphere

the lowest level of Earth’s atmosphere, where most weather takes place

volcano

a place where material from a planet’s mantle erupts on its surface