NASA's Perseverance account and the peer-reviewed paper distinguish at least three water-rock interaction episodes in Jezero crater's Margin Unit. Carbonate and silica occur below the former lake level, while calcium sulfate and fluorite appear in a later fracture; the episodes have not yet been dated.
The Margin Unit examined with Perseverance's SuperCam instrument is an olivine-rich rock sequence near Jezero's former lakeshore. NASA's account and the Communications Earth & Environment paper distinguish at least three water-rock interaction episodes rather than one wet interval. The researchers used the positions of minerals in layers and fractures to establish a relative sequence.[1], [2]
The first pattern is coarse crystalline olivine that remains little altered high in the unit. Rocks below the former lake level instead contain carbonate and silica together, which the team interprets as alteration associated with lake water or shallow groundwater. Calcium sulfate and fluorite in a vein that formed later point to fluid movement separate from that earlier process.[1], [2]
The mineral relationships show which events came first, but not when each episode occurred. The study also does not present these minerals as evidence of past life. The result is a geological record showing that water contacted rocks in this part of Mars more than once under different conditions; the duration, temperature and extent of possible subsurface connections remain open.[1], [2]
