The following is an extract from a paper presented by James Lovelock at the United Nations University in Tokyo in 1992 entitled ‘The Evolving Gaia Theory’. It describes a mathematical model called Daisyworld which is designed to show how life is maintained on earth. Read the extract.
….Imagine a planet just like Earth, and orbiting a star just like the sun. This imaginary planet has a surface of bare earth, but is well watered and capable of supporting plant growth. It is seeded with daisies of two different colours, one dark and the other light. The star that warms Daisyworld is like our own sun, one that warms up as it grows older… At the start of the first season, after the planetary temperature reaches 5 degrees Celsius*, daisy seeds begin to germinate…. (Lovelock, 1992).
Now see if you can predict what will happen on the hypothetical planet to surface temperature, and the populations of dark and light daisies as the sun increases in size and luminosity. Make your predictions using two line graphs.
Graph 1 should also have Solar Luminosity (ranging from 0.2 to 2.0**) on the horizontal axis and % cover or area of daisies on the vertical axis. You will need to draw two lines: one for the % cover of dark daisies, one for % cover of white daisies.
Graph 2 should have Solar Luminosity on the horizontal axis (ranging from 0.2 to 2.0) and Temperature on the vertical axis (ranging from -50°C to 100°C). For this graph you will also need to draw two lines: one representing temperature in the absence of daisies, the other representing temperature in the presence of daisies.
Please note:
*When the surface temperature reaches 5°C solar luminosity is approximtely 0.6.
**When solar luminosity reaches 2.0, the star is at the end of its life. Temperatures on Daisyworld would reach such extremes and no forms of life could survive.
Once you have completed your graphs be prepared to describe and to justify them. Afterwards, follow the link below and compare your answers with the graphs generated by the Diasyworld computer program.
Daisyworld graphs
Discussion Question
What phenonemon stabilizes temperature on Daisyworld?
