April of 2006 mineral deposits, such as those found by the rovers,
enabled scientists to establish a new geological history of Mars.
history is now defined in three distinct geological periods, corresponding
to the dominant minerals that were present.
age, the Phyllocian era, lasted from just after the planet's birth
to about four billion years ago. Ancient rocks show the presence
of clay-rich minerals - phyllosilicates - which, to form, would
have required a water-abundant alkaline environment.