In the Confidence Hills and Mojave 2 samples, scientists found clay minerals, which generally form in the presence of liquid water with a near-neutral pH, and therefore could be good indicators of past environments that were conducive to life. The other mineral discovered here was jarosite, a salt that forms in acidic solutions. The jarosite finding indicates that there were acidic fluids at some point in time in this region.
Additionally, there are different iron-oxide minerals in the samples, reflecting the oxidation of the rock minerals as they reacted with oxygen. This tells scientists the water in the lake changed over time.
In their paper, published in Earth and Planetary Science Letters, the researchers discuss two hypotheses to explain this mineralogical diversity. The lake waters themselves at the base were oxidizing, so either there was more oxygen in the atmosphere or other factors encouraged oxidation.
Another hypothesis is that the groundwater changed over time, and that the environmental conditions present in the lake and in later groundwater were quite different. But both offered liquid water and a chemical diversity that could have been favorable for microbial life.
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“We have all this evidence that Mars was once really wet but now is dry and cold,” Rampe said. “Today, much of the water is locked up in the poles and in the ground at high latitudes as ice. We think that the rocks Curiosity has studied reveal ancient environmental changes that occurred as Mars started to lose its atmosphere.”
The question is, how long did the water remain on Mars, and was it long enough for life to flourish?
These findings, along with all of the data gathered during Curiosity’s mission, are helping to give scientists a full picture of ancient Mount Sharp, where the rocks appear to be made from the silt that settled out from the lakes.
In my book, Incredible Stories From Space: A Behind-the-Scenes Look at the Missions Changing Our View of the Cosmos, Mars Science Laboratory project scientist Ashwin Vasavada explained that the explanation that best fits the “morphology” in this region — that is, the configuration and evolution of rocks and land forms — is that rivers formed deltas as they emptied into a lake. This likely occurred 3.8 to 3.3 billion years ago. The idea is that the rivers delivered sediment that slowly built up the lower layers of Mount Sharp.
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“The entire lower few hundred meters of Mount Sharp were likely laid down by these river and lake sediments,” Vasavada explained. “That means this event didn’t take hundreds or thousands of years; it required millions of years for lakes and rivers to be present to slowly build up, millimeter by millimeter, the bottom of the mountain.”
For this to be possible, Mars also needed a thicker atmosphere than it has now, and a greenhouse gas composition that Vasavada said they are still working on figuring out.
But then Mars lost its magnetic field as the planet — which is roughly half the size of Earth — cooled off more quickly. Mars subsequently lost its atmosphere and water, which very likely means that any life that was starting to flourish was lost, leaving Mars the dry barren planet it is today.
Vasavada noted that the Curiosity rover landed in exactly the right place, because here in one area is a record of much of the Red Planet's environmental history, including evidence of a major shift in the planet’s climate, when the water that once covered Gale Crater with sediment either dried up or was lost to space.
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