Environmental Studies AS - Conditions for Life on Earth (The early…
Environmental Studies AS - Conditions for Life on Earth
Features of the Earth
How the features of the Earth create conditions that are suitable for life:
Gravitational attraction between Moon and Earth
Keeps the Earth's orbit nearly upright in relation to its movement around the sun.
Produces seasonal climatic changes.
Deflects harmful solar radiation.
Controls the force of gravity.
Strong enough to retain an atmosphere.
Speed of rotation
Prevents excessive temperature fluctuations.
Distance from Sun
Controls amount of insolation, and therefore temperature and presence of liquid water.
Effect of presence of life on environmental change
Atmospheric carbon dioxide
Carbon dioxide is naturally released into the atmosphere by volcanoes.
It's an essential GHG, helping to retain heat in the atmosphere.
Without carbon dioxide, it'd be too cold for life.
Excessive carbon dioxide causes too high temperatures for life.
Living organisms have helped maintain suitable atmospheric temperatures by removing carbon dioxide from the atmosphere and storing it in
The Sun's light output increases by
10% every billion years
It is now
since life first developed.
If carbon dioxide content remained constant, the Earth would have heated up and life would have died out.
The water cycle
Heat energy from absorbed sunlight causes sea water to evaporate.
This may fall as rain over land and flow back into the sea.
Most rain falls relatively close the coast, but
in places returns water vapour to the atmosphere to be blown further inland.
Transpiration from leaves is unavoidable as the moist stomata must be open to allow
Important in cooling plants and upward transport of dissolved minerals.
Individual Earth features and their inter-connections can be very complex.
Although interdependent, often easy to focus on one aspect at a time.
Continued presence relied on processes to continually replace it.
Small amount was released by the
photolysis of water
, then, much later,
gradually released larger amounts.
This oxygen absorbed UV light from the sun, causing molecules to split, producing
which reacted with
This allowed the
to develop, providing protection from UV light to living organisms.
Before this, abundant life was not possible on land so early organisms lived in the oceans where water protected them from UV light.
Oxygen is a reactive element.
Concentration declined as it reacted with other elements.
The early conditions on Earth
Large amounts of water
Most chemical reactions in cells take place dissolved in water.
Water is the solvent in blood and sap.
Transports oxygen, carbon dioxide, sugars, amino acids, waste products, mineral nutrients, etc.
Evaporation of water from the skin can be used to cool the body if too hot.
Heat can also be transported in the blood.
Functions in the wider environment
Provision of aquatic habitats
such as rivers, lakes and oceans.
Anomalous expansion on freezing
Ice separates the cold air above from the water below, preventing the water from cooling.
Prevents lakes in cold areas from freezing solid.
High specific heat capacity
Causes water to warm up and cool down slowly.
Helps moderate the rate and size of temperature changes.
Appropriate temperature range
Most areas of Earth have temperatures above 0°C, allowing presence of liquid water.
Most enzymes require liquid water as a solvent and denature at higher temperatures.
Therefore, most living organisms found within 0°C to 40°C range.
Suitable ambient gases
Suitable ambient gases for developing and sustaining life are:
Carbon dioxide - photosynthesis and climate control.
Nitrogen - protein synthesis.
Light and radiation from the sun
Conditions resulting from Earth's position and structure
Distance from Sun
Controls light levels and temperatures.
Controls day/night durations and temperature range.
Produces seasonal variations.
Produces magnetic field deflecting harmful radiation.
Conditions resulting from Earth's features
Provides energy for photosynthesis.
Heat production when absorbed
Energy source for the water cycle and Earth warming.
Little harmful ultraviolet (UV) and ionising radiation