Earth’s Subsystems and Related Concepts

Vocabulary flashcards that cover key terms related to Earth’s subsystems, atmospheric layers, geosphere structure, hydrologic processes, and biological hierarchy.

Earth’s Subsystems

The four interacting parts of the planet—atmosphere, hydrosphere, geosphere, and biosphere—across whose boundaries matter and energy flow.

Atmosphere

The envelope of gases surrounding Earth, composed mainly of 78% nitrogen and 21% oxygen, providing UV protection and greenhouse warming.

Hydrosphere

All water on Earth in solid, liquid, and gaseous forms, covering ~71 % of the planet’s surface.

Geosphere (Lithosphere)

All the solid rock on Earth—from crustal grains of sand to the inner core—including mountains, mantle, and core layers.

Biosphere

The global sum of all living organisms and the zones in which they exist.

Troposphere

Lowest atmospheric layer containing ~75 % of the air and nearly all water vapor; weather occurs here and temperature drops 6.5 °C / km.

Stratosphere

Atmospheric layer above the troposphere; houses the ozone layer and shows temperature increase with altitude due to UV absorption.

Ozone Layer

Region in the stratosphere rich in O₃ molecules that absorb harmful ultraviolet radiation and protect living organisms.

Mesosphere

The coldest atmospheric layer (~ −100 °C) where meteoroids burn up; air is extremely thin and has little weather influence.

Thermosphere

Hottest atmospheric layer (200 – 500 °C) owing to strong solar radiation absorption; contains atomic O, N, and He.

Greenhouse Gases

Atmospheric gases such as water vapor and CO₂ that trap heat and keep Earth warm enough to sustain life.

Nitrogen (N₂)

Most abundant atmospheric gas (78 %) that is relatively inert under normal conditions.

Oxygen (O₂)

Second-most abundant atmospheric gas (21 %) essential for aerobic respiration.

Lithosphere

Rigid outer part of Earth comprising the crust and uppermost mantle.

Crust

Earth’s outermost solid shell; thinnest layer, composed mainly of oxygen, silicon, and aluminum.

Continental Crust

Older, thicker, less-dense portion of crust forming continents.

Oceanic Crust

Younger, thinner, denser crust beneath oceans.

Mantle

Thickest Earth layer (84 % volume) of mostly solid silicate rocks with semi-molten regions.

Asthenosphere

Plastic, partially molten upper mantle zone that allows tectonic plates to move.

Outer Core

Liquid iron–nickel layer generating Earth’s magnetic field; temperatures 4 500–5 500 °C.

Inner Core

Solid, dense ball of iron at ~5 200 °C; remains solid due to extreme pressure.

Hydrologic Cycle

Continuous movement of water among ocean, land, and atmosphere via evaporation, condensation, and precipitation.

Evaporation

Process where liquid water becomes vapor, driven mainly by solar energy and wind.

Condensation

Change of water vapor to liquid, forming clouds and fog around cloud-condensation nuclei.

Precipitation

Any liquid or solid water (rain, snow, hail) that falls from the atmosphere to Earth’s surface.

Runoff

Movement of liquid water across land toward streams and oceans.

Transpiration

Release of water vapor from plant stomata into the atmosphere.

Sublimation

Direct transition of solid water (ice) to vapor without becoming liquid.

Percolation

Downward movement of water through soil layers toward groundwater.

Infiltration

Process by which surface water soaks into the ground.

Atom

Smallest unit of an element that retains its chemical properties; starting level of biological hierarchy.

Molecule

Two or more atoms bonded together; building blocks of cells.

Cell

Basic unit of life; some organisms (e.g., bacteria) consist of a single cell.

Tissue

Group of similar cells performing a specific function.

Organ

Body part composed of different tissues working together (e.g., heart, leaf).

Organ System

Network of organs performing broad functions (e.g., circulatory system).

Organism

Individual living being in which all organ systems work as a whole.

Population

Group of individuals of the same species living and interacting in a shared area.

Community

Populations of different species that live and interact in the same place.

Ecosystem

Community of organisms plus the physical environment in which they interact.

Biome

Large region defined by climate, physical environment, and distinctive biological communities.