the boundary between air masses of different densities and usually different temperatures

in the orbit of a planet or other body in the solar system, the point that is farthest from the sun

the quality of a rock that is based on the sizes, shapes, and positions of the rock's grains

the movement or trembling of the ground that is caused by a sudden release of energy when rocks along a fault move

the water that is beneath Earth's surface

the standard method used to divide Earth's long natural history into manageable parts

any method of determining whether an event or object is older or younger than other events or objects

stress that occurs when forces act to stretch an object

the moment when the sun appears to cross the celestial equator

describes something that uses Earth as the reference point