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 Automatic translation  Automatic translation Category: evolution
Updated June 26, 2013
  circumstellar habitable zone or ecosphere

image: The habitable zone is not a fixed area, it changes according to the age, the temperature of the star and the presence of CO2 in the atmosphere of the Earth. During their evolution stars becoming more brilliant and hotter and hotter, the habitable zone is thus logically away from the star. A planet will therefore remain very long, billions of years in this area, to synthesize all the molecules necessary for life form. We do not know why it takes so long. Bacterial life appeared there are 3.8 billion years multicellular life 1.4 Ma ago, the first animals there are 600 million years. In summary to maintain liquid water must stay very long in a habitable zone but also keep an atmosphere. In the picture, the green area is the living area, tapering terribly over time, too close to the star it is too hot, too far away it is too cold.

    
  carbonate silicate cycle

Image: Diagram illustrating the carbonate-silicate cycle.
credit: J. F. Kasting, Science Spectra, 1995, Issue 2, p. 32-36. Adapted from J. F Kasting, 1993.

    
  type and class of stars

Image: The Sun is of spectral type G. A star is characterized by its color (its spectral type), and its luminosity. For a given spectral type, more the star is greater, more its heat is increased and more its brightness is high. The O and B stars are blue, the A stars are white, F and G stars are yellow, the K stars are orange, M stars are red.

    
 state of pure water according to the temperature and pressure  

Image: The water remains liquid when the atmospheric pressure is above the triple point that is greater than 6.1 mb. The temperature must be above 0 ° C, and finally it must be below the boiling point, which depends on the pressure points. Just above the triple point (0.006 atm) just a few degrees so that the water remains liquid. Earth is between 0 ° C and 100 ° C. If there is sufficient pressure (218 atm), water remains liquid up to 374 ° C. State transition diagram or phase transition of pure water. The triple point, the 3 phases coexist in a temperature and pressure. The critical point (218 atm, 314 ° C) between the gas and liquid transition, the water reaches the fluid phase, the gas and liquid time.

 
           
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