The presence of water is an essential requirement for the formation of life

• The polarity of water will cause non-polar lipids to spontaneously form lipid bilayers when in solution

• The thermal properties of water will help to maintain a stable internal environment needed for homeostasis

• Water will dissolve any polar or charged substance, making it an excellent medium for metabolic reactions

• The assembly of complex organic molecules requires water as a reagent (condensation polymerisation)

Water on Earth

When the Earth was forming, the materials involved in its accretion would have contained a sizeable quantity of water vapour

• However, high temperatures would have prevented this water from condensing and low gravity would have resulted in most of the vapour being lost to space

Consequently,the large bodies of water on Earth are hypothesised to have instead originated from asteroids formed further from the Sun

• These asteroids formed at a distance from the Sun where the cooler temperatures would have allowed the water to be frozen as ice

• When the asteroids collided with Earth, the planet had achieved sufficient mass (and gravity) to retain the water and had cooled enough for it to condense

Extraplanetary Origins