Stars and Planets » Earth Type Planets and Variations

Our Earth is often referred to as a 'Goldilocks World' because it has just the right conditions on which life can arise and evolve. Let us look at those parameters which seem to favour the existence of life on Earth.

  • The Earth is at the right distance from its star for liquid water to exist in the liquid state for very long periods of geological time.
  • Earth is massive enough to be able to prevent the escape from the atmosphere in large amounts of all gases except molecular hydrogen and helium. If its gravity pull as recognised by the escape velocity were too low causing the escape velocity to be low it would be like the Moon and Mercury with no atmosphere. It should also be noted that there is a limit to the mass since if it had a high enough gravity giving a high escape velocity then hydrogen and helium would be maintained in the atmosphere. Such a superearth would be likely to grow into a gas giant by sweeping in these gases from interplanetary space.
  • Plate Tectonics operates on the Earth and it is thought to be aided by the presence of water as a lubricant.
  • The presence of the Moon seems to favour the evolution of life because it prevents wild changes in the angle of tilt of the axis which could cause great instability in the climate.
  • The presence of a magnetosphere protects the surface from the worst ravages of the Solar Wind.
  • There is a good balance of chemical elements which favour the existence of life. The presence of large quantities of the chemical element OXYGEN gives us large quantities of water and silicate rocks.
  • Oxygen is far more abundant than nitrogen which militates against the formation of ammonia based biochemistry and life.
  • Oxygen is far more abundant than carbon. It has been suggested that earth-sized planets where oxygen was of low abundance and carbon much higher could give rise to rocks made of silicon carbide and carbon itself even in the form of mountains made of diamonds. A high carbon/oxygen ratio could give rise to carbon monoxide as the prevelent gas rather than dioxide. Also methane would predominate over water.

Ray Goodwin

Somewhere there are mountains
Glistening in the snow
Somewhere there are mountains
That we shall never know

Somewhere there are rivers
Flowing fast and free
Somewhere there are rivers
That we can never see

Somewhere there are oceans
And sun drenched island sands
Forests full of creatures
In vastly distant lands

Somewhere there’s a planet
Beneath an alien star
The people watch our tiny sun
And wonder where we are

One day perhaps we’ll find them
Across the void of space
Perhaps through ways as yet unknown
We’ll meet them face to face

The author of this web site Ray Goodwin holds B.Sc. Degrees from London University in Chemistry, Geology and Physiology and an M.Sc. in Biochemistry. He has spent most of his professional life teaching in Colleges of Technology. On his retirement he has entered the fields of astronomy, astrochemistry, astrobiology and space sciences. He has spent a great deal of his retirement in visiting amateur astronomy societies and in attending European Space Agency Symposia in ESTEC in the Netherlands and other scientific conferences in England and Sweden. He regularly attends the yearly European Astrofest in South Kensington London and other meetings in the UK. He has written scientific articles and given a number of lectures on diverse scientific subjects.

Readers of this web site are invited to e-mail the author ( and discuss their opinions of the topics dealt with and suggest any changes which they think may be helpful.

Life in the Cosmos Website
Version 01.00 - April 20, 2015.