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In conclusion, if an extraterrestrial (or extrasolar) observer was looking at the
Earth from an astronomical distance, and similarly if we were observing an Earthlike
exoplanet, we would be able to determine some of its properties. From al these
properties, those regarding the possibility of finding life would be:
• Habitability signatures:
Variability and albedo
Spectral shape (Rayleigh scattering, atmospheric properties)
Presence of oceans (glint)
Presence of dynamic weather ... and possibility of liquid water
• Life signatures:
Atmospheric disequilibrium caused by life
• Complex life (plant/animal) signatures:
Presence of complex life (red or other edges)
Presence of biomass from circular polarization