Earth’s Water

How is water distributed on Earth?• remains fairly constant• 97% is saltwater –

unusable• most freshwater (69%) is

ice – polar ice caps, glaciers, etc.

• 30% of freshwater is groundwater

• .3% (of the 3%... that is .09% of all water) is surface water

• You are drinking water that dinosaurs could have swam in, drank, etc.

What is the hydrologic cycle?• the movement and storage of water in the

hydrosphere• http://www.epa.gov/safewater/kids/flash/flas

h_watercycle.html

How does water move through the cycle?

• Evaporation (includes transpiration)

• Condensation• Precipitation• Collection/

storage

How does water evaporate?1. Solar energy adds heat

energy.2. Water molecules absorb

heat energy.3. Heat energy speeds up the

molecules. 4. Water changes from a

liquid state into a gas state (vapor).

sweat

transpiration

What causes condensation?

1. Water vapor releases heat energy.

2. Water vapor molecules change from a gas state to a liquid state.

What causes precipitation?

Gravity!

How is water collected?

Surface Water• river systems

(watersheds)• oceans• runoff

Groundwater• infiltration/percolation• aquifers• can discharge to surface

water

What is groundwater?

permeable –allows water to pass through

pores in zone of aeration

water table – must drill below for water

Impermeable - bedrock