Since it landed on Mars in February 2021, the rover Perseverance has been exploring Jezero Crater, a 50-kilometer-wide impact feature. The mission’s purpose is to look for evidence that Mars once had or maybe still has areas that can support life .  Jezero was chosen as the landing site because it was very clearly a lake of standing water at some point in the past. Orbiters detected minerals that form in water there, and in the northwest part of the crater are the remains of an enormous fluvial delta formation, sediment deposited as water flowed into the crater eons ago — think Nile delta and you’ve got it. You might expect, then, that the floor of the crater would be loaded with sedimentary rocks; minerals deposited as silt and grains of other material settled down to the lake bed, were compressed, and formed layered rock. But geology is sneaky, even — or especially — on Mars, and can trick you.…