EARTHSCI LESSON 3

earth as a system and its subsystems

Stages of Accretion

Accretion forms planetisimals, which form protoplanets. A protoplanet is a planetary embryo that consists of a collection of matter, from which a planet is formed.

Homogeneous Accretion

Earth accreted from materials of the same composition after condensation.

Heterogeneous Accretion

Earth accreted during condensation, forming a differentiated planet as it grew in size.

Gaia Hypothesis

Earth and its biological systems behave as one huge single entity with self-regulatory feedback loops keeping conditions favorable to life.

System

A set of interconnected components that are interacting to form a unified whole.

Earth as a Closed System

A closed system is one where there is only exchange of heat/energy and no exchange of matter.

Earth’s Four Major Subsystems

Atmosphere: thin membrane of air around planet; Hydrosphere: Earth’s water in liquid, ice, vapor; Geosphere: hot core, thick mantle, thin crust; Biosphere: includes parts of atmosphere, hydrosphere, geosphere.

Albedo

Property of absorbing or reflecting light; value from 0–1 (0 = absorbs, 1 = reflects).

The Sun

Earth’s main source of energy, powers planetary processes; plants depend on it for photosynthesis.

Solar Energy as Renewable

As long as the Sun shines, energy is available; environmentally friendly.

Earth’s Energy Budget

Balance of absorbed vs reflected energy; 30% of Sun’s energy is reflected/scattered by clouds, atmosphere, surfaces.

Atmosphere

Mixture of invisible gases surrounding Earth; extends ~500 km; most gases within 8–12 km.

Atmospheric Composition

78% nitrogen, 21% oxygen (~99% together); 0.9% argon; 0.1% trace gases; CO₂ and ozone essential for life.

Layers of the Atmosphere

Troposphere: lowest, weather, biosphere, ~12 km; Stratosphere: ozone layer, above troposphere; Mesosphere: meteorites burn, coldest; Thermosphere: extremely high temps; Exosphere: outermost, contact with space.

Atmospheric Circulation

Heat redistributed by circulation; constant heat/moisture exchange with hydrosphere via hydrologic cycle.

Energy Flow in Atmosphere

Solar radiation heats unevenly; cold air sinks, warm rises; convection distributes energy.

Atmosphere in Hydrologic Cycle

Atmosphere is reservoir of water, medium for moving it around the globe.

Geosphere

Solid Earth (continental, oceanic crust, interior layers); 94% of Earth is oxygen, silicon, magnesium; constantly changing surface; source of minerals; layers classified by composition & physical properties.

Hydrosphere

Origin hypotheses: from comets or trapped volatiles in magma; contains all water on Earth.

Water Properties

a) hydrogen bonds; b) liquid over wide range; c) stores heat; d) high energy to evaporate; e) dissolves compounds; f) filters UV; g) capillary action.

Water Distribution

97.5% saltwater, 2.5% freshwater.

Energy Flow in Hydrosphere

Sun heats ocean unevenly; temps vary equator–poles, decrease with depth; salinity & density cause convection currents distributing energy.

Biosphere

Living part of Earth; includes organisms & undecomposed organic matter; composed mainly of C, H, O, N; includes all ecosystems from rainforest to deep sea.

Chemosynthetic Organisms

Use energy from hydrothermal vents or methane seeps to produce sugars.

Earth System Science

Study of continual interactions among atmosphere, hydrosphere, geosphere, biosphere.