At the end of this era, intense volcanic activity coupled with the release of gases and sulphur into the atmosphere caused an acidic environment.
Water is thought to have been present on the planet surface at this time.
It is also thought that the atmosphere became thinner, due to radiation or violent impacts.
As volcanic activity ceased, the water progressively disappeared, leaving behind sulphate deposits.
Finally, rocks exposed to the atmosphere were slowly but steadily oxidized. In the absence of water, iron turned into iron oxide.
These molecules, in the form of hematite crystals, give the planet its characteristic red colour.
In the light of these recent data, the Phyllosian era is the most likely to have supported life.
Consequently, the clay beds formed during this period provide targets for future investigations to search for clues.
* OMEGA: Observatoire pour la Minéralogie, l’Eau, les Glaces et l’Activité, developed by the IAS space astrophysics institute (France), LESIA space and astrophysics instrumentation research laboratory (France), IKI space research institute (Russia) and IFSI interplanetary space physics institute (Italy).
Global Mineralogical and Aqueous Mars History Derived from OMEGA/Mars Express Data
Jean-Pierre Bibring, Yves Langevin, John F. Mustard, François Poulet, Raymond Arvidson, Aline Gendrin, Brigitte Gondet, Nicolas Mangold, P. Pinet, F. Forget, the OMEGA team; 2006, Science Vol. 312, pp 400-403