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Phoenix
also detected calcium carbonate, a chief component of limestone
rock, which, like the phyllosilicates that characterise the Phyllocian
era, can only form in the presence of liquid water. The orbiters
have found such minerals in other parts of Mars, but in regions
that have clear evidence of former flowing water. The Phoenix landing
site is an open plain without obvious features carved by flowing
water. This suggests that ice melted in-situ and stayed in that
area.
Glacial deposits
near the equator on Mars are believed to be remnants of ancient
snow. Ice -rich landforms and scattered boulders appear to have
been caused by glaciers between 350,000 years to 4 million years
ago, the end of the Theikian Era.
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