Explains the importance of water for life on Earth, the water cycle as a system, stores in the global water cycle (e.g. the atmosphere, oceans, ice caps, aquifer systems), and the drainage basin water cycle and the flows of this. Also includes an explanation of flood hydrographs and the water balan...
Earth’s Life Support Systems SG1
The Water Cycle – An Introduction
The Importance of Water for Life on Earth
Why is Earth the only planet that can support life in all its forms?
We have water – clouds, oceans, water vapour
- All life on Earth relies on liquid water
‘Goldilocks Zone’ – habitable zone
- Not too hot or cold
- Water
Clouds, water vapour and oceans regulate temperature
- Clouds reflect 1/5 incoming solar radiation – high albedo
- Water vapour absorbs long wave radiation from Earth
- Ocean currents transfer heat
Liquid water is important for it is essential for life on earth – for the climate, people, flora and fauna:
People Flora
● Water is essential for economic activity – ● Plants need water to photosynthesise. They need
generating electricity, growing crops, manufacturing to photosynthesise, to make glucose and starches to
etc. grow.
● We need water in our bodies so we can sweat and ● Plants need water for rigidity.
cool ourselves down. ● Transport nutrients from the soil.
● Used for chemical reactions in the body and the ● Transpiration
circulation of oxygen and nutrients. ● Growth and reproduction
● Respiration ● Metabolic function
● Drinking
● Metabolic function
● Growth and reproduction
Fauna Climate
● Used for chemical reactions in the body and the ● Oceans absorb, store and release heat slowly =
circulation of oxygen and nutrients. regulate temps around the year.
● Animals need water in our bodies so they can ● Clouds reflect 1/5th of incoming solar radiation
pant to cool themselves down – evaporate cooling and lower surface temperatures.
● Respiration ● Water vapour absorbs long-wave radiation
● Reproduction and growth helping to maintain average global temperatures.
● Metabolic function ● Ground water
● Chemical reactions ● Precipitation
● Evaporation
The Water Cycle as a System
The global water system is a The global water system
ATMOSPHERE
closed system as it consists of three stores:
only transfers energy, Precipitation ● Atmosphere
not matter, Evaporation Evapotranspiration ● Land
between the ● Oceans
sun and Earth.
Precipitation LAND
OCEAN Run off/ groundwater
, Stores in the Global Water Cycle
Stores or stocks – the total amount of the material of interest held within a part of the system.
Stocks – expressed in units of mass
Stores – measured in thousands of cubic kilometres (x 10 3 km3)
Key Term Definition
The rigid outer part of the earth, consisting of the crust
Lithosphere
and upper mantle. It is divided into tectonic plates.
The space at the Earth’s surface and within the
Biosphere
atmosphere occupied by living organisms.
All the waters on the Earth’s surface, for example lakes
Hydrosphere
and seas.
The frozen part of the Earth’s surface, including the
Cryosphere polar ice caps, continual ice sheets, glaciers, sea ice and
permafrost.
Atmosphere The envelope of gases surrounding the planet.
Represents all of Earth’s water. It has a diameter of 860 miles. This includes water in lakes,
oceans, ice caps, rivers, groundwater and atmospheric water.
This represents the world’s liquid fresh water (groundwater, lakes, swamp water and rivers). It
has a diameter of 169.5 miles. 99% of the groundwater is not accessible to humans.
This represents the freshwater in the lakes and rivers on earth. It has a diameter of 34.9 miles. Most
of the water used by people, plant and animals need comes from these surface water sources.
LAND: <3% ATMOSPHERE: <0.1% OCEAN: 97%
Store % of global water Residence time – how long the
water is stored there
Oceans 97% 3,600 years
Polar ice and glaciers 2% 15,000 years
Groundwater (aquifers) 0.6% Up to 10,000 years
Lakes 0.01% 2 weeks – 10 years
Soils 0.005% 2 – 50 weeks
Atmosphere 0.001% 10 days
Rivers 0.0001% 2 weeks – 10 years
Biosphere 0.00004% 2 – 50 weeks
20% of all freshwater is stored in rocks below the ground surface, as underground reservoirs called
aquifers.
Aquifers mainly form in rocks such as chalk and sandstone, which are porous and permeable. This
causes uneven distribution.
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