Topic 1 - Conditions for life on Earth

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Water (amount and form)

The early conditions on Earth

Large amounts of water

Water is essential to all living organisms, both for its physiological functions in living organisms and for the way it changes the wider environment. 

  • Physiological solvent - most chemical reactions in cells take place dissolved in water.
  • Transport - water is the solvent in blood and sap. It transports oxygen, carbon dioxide, sugars, amino acids, waste products, mineral nutrients etc.
  • Temperature control - the evaporation of water from the skin can be used to cool the body when it is too hot. Heat can also be transported in the blood, for instance from the core of the body to the skin to increse heat loss.
  • Anomalous expansion on freezing - because ice floats it keeps very cold air above the ice separate from the water below, which prevents the water from cooling as muvh as it would have without the ice. This prevents lakes in cold areas from freezing solid in winter.
  • High specific heat capacity - this causes water to warm up and cool down slowly, helping to moderate the rate and size of temperature changes.
  • Provision of aquatic habitats - such as rivers, lakes and oceans.
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Appropriate temperature range

The early conditions on Earth

Appropriate temperature range

  • Most areas of Earth have temperatures above 0°C, which allows liquid water to be present.
  • Most enzymes require liquid water as a solvent and denature at higher temperstures.
  • So most living organisms are found within the range 0°C to 40°C.
  • Some organisms, such as thermophilic bacteria, can withstand much higher temperatures, sometimes over 80°C.
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Suitable ambient gases

The early conditions on Earth

Suitable ambient gases

Suitable ambient gases for developing and sustaining life are:

  • Carbon dioxide (for photosynthesis and climate control)
  • Nitrogen (for protein synthesis)
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Light and radiation from the sun

The early conditions on Earth

Light and radiation from the sun

  • Sunlight - provides the energy for photosynthesis.
  • Heat production when absorbed - the source of energy for the water cycle and warming the Earth.
  • Little harmful ultraviolet and ionising radiation.

Some of these conditions are the result of the position of the Earth in the solar system, while others are the result of features of the Earth itself.

  • Distance from the Sun - controls light levels and temperatures.
  • Daily rotation - controls the duration of day and night, and therefore the range of temperatures.
  • Tilted axis - produces seasonal variations.
  • Molten layers beneath crust - produce the Earth's magnetic field which deflects harmful radiation coming from the Sun.
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