Revision notes - origins of life on Earth, chemistry of life

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8.4.1 Origin of life Identify the r/ship between the conditions on early Earth and the origin of organic molecules

  • Early earth contained no ozone layer → large amounts of UV radiation reached the earth
  • Little free oxygen (anoxic) therefore no ozone layer.
  • The volcanic emissions filled the atmosphere with methane (CH4), ammonia (NH3), H, CO2, CO and small amounts of water vapour.
  • The violent electrical storms and acidic rain formed the present warm and mineral-rich oceans.
  • There are only two possible ways organic molecules could have formed either - formed on earth from simpler molecules (Abiogenesis)
            - arrived from the cosmos (Panspermia) Discuss the implications of the existence of organic molecules in the cosmos for the origin of life on Earth


  • Elements found in space (H, He, C, O, N, P) can combine to form organic molecules.
  • Some of these compounds including amino acids have been found in meteors that have struck the earth’s surface.
  • Panspermia proposes that living organisms were seeded on earth as passengers on comets and meteors (ie. Life evolved elsewhere and travelled to earth) Describe two scientific theories relating to the evolution of the chemicals of life and discuss their significance in understanding the origin of life


  • Formation of complex organic molecules on earth via undersea thermal vents (black smokers)
  • Life may have evolved in these areas using chemical energy available from vents.

Abiogenesis (Urey-Miller)

  • Life on earth arose from organic molecules existing on the primitive earth (amino acids – basic building blocks of life)


  • Suggests either very primitive organisms or complex organic compounds travelled to earth from space.

In each theory, before life could have originate/evolve complex organic compounds first had to be formed. Theories differ in how these precursors formed → shallow oceans (Urey-Miller); formation of chem. rich compounds (vents); complex molecules in space (panspermia). Discuss the significance of Urey and Miller's experiments in the debate on the composition of the primitive atmosphere

  • Urey and Miller set up simulation of primitive earth.
  • A mixture of H2, ammonia (NH3), and methane (CH4) in the form of steam was continuously electrically discharged (lightening) for a week.
  • Resulted in a solution containing amino acids and hydroxy acids → vital components for living things.
  • Urey and Miller’s experiment supported Oparin and Haldane’s theories on the origin of life, which showed that organic material could be formed by raw materials. Identify changes in technology that have assisted in the development of an increased understanding of the origin of life and evolution of living things

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Radiometric Dating

  • Radioisotopes decay at a predictable rate
  • By measuring the amount of radiation present now, and knowing the ‘half-life’ (the time it takes for the radiation to drop to half the previous level) of the isotope, the age can be calculated.
  • This is how we know the age of the earth
  • Carbon-14 dating

Electron Microscope

  • Allows scientists to study ancient fossil cells in rocks and to make comparisons with ‘primitive’ cells that exist today
  • Provides info about how ancient life forms lived and evolved

Biochemical Analysis and DNA technology

  • Used ...

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This is a very well detailed set of notes about early life and classification. It is wirrten in easy to digest bullet points and is reasonably well explained. It is very comprehensive Overall this set of notes is 5 stars out of 5.