According to a few sources, including the Hesparonaut Armor, it would appear that we terraformed the planet, (or at least Venus), as it mentions humans and terraforming machines, which might explain why Venus ended up differently than Mars... Or something to that effect...
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According to some lore and crucible maps, mars after it got terraformed had forests and different ecosystems. Sadly I believe the sand took back mars after the collapse
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Also a good point.
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The oasis map with the jump points is a great example of this.