2. Origin of life

It is still a challenge for scientists and philosophers to define the term “life”, since it must include all life we are familiar with, but also not exclude life forms that might be fundamentally different from life on earth (= Aliens).

Life can be defined as:

• A network of regulatory mechanisms (negative feedbacks) inferior to the potential of expansion and reproduction (positive feedbacks).

• Things with the capacity for metabolism and motion

• Matter that can reproduce itself and evolve as survival dictates

• A way to hydrogenate carbon dioxide

• Living things that are self organizing and autopoietic (produce and maintain without help)

NASAs definition: Life is a self sustained chemical system capable of undergoing Darwinian evolution.

On the one hand life can be seen as a property of an ecological system rather than a single organism, on the other hand the Gaia theory states that life, functions as a single organism which maintains the environmental conditions necessary for it’s survival.

98% of life is built on CHNOPS: Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, Sulphur

• Water:

  • Reactant in many metabolic reactions

  • Starting point of photosynthesis

  • Habitat

  • Main components of all living being

  • Very good solvent for polar compounds

• Carbon:

  • life is obtained from carbohydrates or photosynthesis

  • Structural elements for life (RNA, DNA, cellulose)