Earth as a SystemChapter 3

I.General InfoA. System - a set of components that function together as a whole (e.g. human body, a city, etc.)

B. Earth is an interconnected system1. Comprised of many smaller, complex systems

that operate at multiple space and time scales2. Matter and energy flow through Earth’s systems3. Change in one part of the system affects one

or more other parts = environmental unity

C. Solutions to many environmental problems involve the study of systems and their rates of change

II.Basic System ConceptsA. Types of Systems

1. Open – matter and energy are exchanged with surroundings (e.g. ocean); most Earth systems are open

2. Closed – no exchange of matter or energy occurs (e.g. Biosphere 2)

B. Earth is an open system with regard to energy (sunlight), but a closed system with regard to matter

C. Systems respond to inputs and produce outputs

D. System States1. Steady (static) – fixed condition

where system stays constanta. Equilibrium - inputs equal outputs;

most natural systems exist in this condition

2. Dynamic – changes (often continually) over time (e.g. Missouri river)

Missouri River – Dynamic System

E. Feedback1. Most natural systems are in steady

state and can respond to inputs and outputs using feedbacks

2. Negative feedback loop – system responds to change by returning to its original state; increase in output leads to a decrease in output later (e.g. thermostat)

3. Positive feedback loop – amplifies changes; increase in output leads to increased output later (e.g. population growth, forest fires)

Mono Lake

A. Scientists study systems by measuring flows (inputs and ouputs) and storage to determine changes under various conditions

I = O ± ΔS

I = inputO = outputS = storage

III.Systems Analysis

B.Average residence time (ART)1. Measure of time a substance remains stored in a

system2. Use input-output analysis to derive ART3. Knowing ART for chemicals is important in

evaluating environmental problems (e.g. how long will a molecule of CO2 remain in the atmosphere)

Do “Working it Out 3.1” on page 47 in your CT journal

C.Models1. “Deliberately simplified construct of nature” (e.g.

computer simulation, pictorial or physical model, etc.)

2. Used by scientists to explain accumulated knowledge regarding accepted hypotheses (e.g. global warming) and to predict future change