Earth and Sky

earth science

the study of Earth's structure and composition, as well as the processes that change Earth

solar system

the collection of objects that orbit a star

star

a celestial body that is held together by its own gravity and that releases light

planet

a large, spherical object that orbits a star

moon

a naturally formed object that orbits a planet

asteroids

very small, rocky bodies that orbit the sun

meteoroids

small fragments of asteroids less than tens of meters across

comets

relatively small, icy, dusty bodies that travel around the sun in elliptical orbits

axis of rotation

the imaginary line from the North Pole to the South Pole on which a planet rotates

crust

the outermost rocky shell at the surface of Earth

mantle

 the rocky layer beneath the crust, and the thickest layer of Earth

outer core

the metallic outside layer of Earth's core that is mainly composed of hot iron in a liquid state

inner core

the metallic inside layer of Earth's core that is composed of a solid ball of nickel-iron alloy under extreme pressure

weathering

the alteration or breakdown of rock or soil

physical weathering

weathering that is the result of mechanical processes such as changes in temperature or pressure

chemical weathering

weathering that is the result of chemical processes or reactions that cause a rock's composition to change

erosion

 the mechanism responsible for the transportation or removal of material

deposition

the process by which soil, sediment, or rocks are added to a landform

sand dunes

an example of the eolian process requiring the same three basic elements for formation: a large quantity of loose and unvegetated sand, wind, and an obstacle

river valleys

valleys produced by erosion that form when a river cuts down into the underlying bedrock in a steep V shape

river delta

 the result of the deposition of sediment carried by a river as the flow leaves its mouth and enters slower-moving or standing water such as an ocean or lake

meanders

curves in a river that form as the outer bank of a river erodes while the inner edge is deposited with sediment

glacier

a slowly moving mass of ice formed by the accumulation and compaction of snow

moraines

depositional features formed when glaciers plow up mounds of dirt and rock in front of them and along their sides

glacier valleys

valleys produced by erosion that form when a glacier flows over rock, cutting into it to form a broad U-shape

mineral

 a naturally occurring, solid, inorganic element or compound that is formed by natural processes, has a limited range of possible chemical composition, and has a definite arrangement of atoms

rock

 a heterogeneous mixture of one or more minerals

sedimentary rocks

rocks made up of weathered particles, such as sand, silt, clay, gravel, cobbles, or even occasionally boulders, that have been cemented together into hard rock

igneous rock

rocks formed by lava or magma; molten rock, or lava, cools quickly into rock when it erupts onto Earth's surface

metamorphic rocks

rocks that have been changed from their original form; typically occur when a rock is partially buried and exposed to elevated temperatures and pressures that are not extreme enough to melt the rock completely

rock cycle

the various processes that change rocks from one form to another

atmosphere

 the layer of gases surrounding Earth and other planets

troposphere

the lowest and densest layer of Earth's atmosphere, where weather occurs

stratosphere

the layer of Earth's atmosphere that contains the ozone layer

ozone layer

the layer of Earth's atmosphere that protects it from harmful sun radiation

mesosphere

the middle layer of the atmosphere, where meteor showers can occur

thermosphere

the layer of Earth's atmosphere where the auroras occur and objects like the International Space Station are in orbit

exosphere

the layer of Earth's atmosphere where the atmosphere thins and merges with outer space

air mass

a large volume of warm or cold air that has approximately uniform temperature, humidity, and pressure over hundreds or thousands of miles horizontally and up to about 16 km vertically

air density

 the amount of air present in a given volume

air pressure

the force that an air mass pushes on the surrounding area

front

a boundary between two or more air masses

warm front

 the leading edge of a moving mass of warm air that pushes into a mass of cold air

cold front

the leading edge of a moving mass of cold air that pushes into an area of warm air

high pressure system

an area that has a pressure higher than the surrounding air masses

low pressure system

 an area that has a pressure lower than the surrounding air masses