Valles Marineris - How do young earthers explain ancient geology on other planets?

Well, there are some things that God would have been obliged to do if he wanted a universe that worked from day one. Obviously creating the sun would have been one of those things, because life on earth would be impossible without it. Similarly he'd have needed to make the sea salt, or he'd have nowhere to keep all the salt-water fish; and he'd have needed to make soil without waiting for sub-aerial weathering to take place, or the plants would have had nowhere to grow.So much we can grant. But you slip into omphalism when you start supposing that he could have gratuitously made the universe look old for no apparent reason except to screw with scientists.

It's more usually translated as "God is subtle, but he is not malicious".

I think I've drawn the line.If God necessarily had to give the Earth certain appearances of age when he magicked it into being, then you're OK.But when you have to suppose that God might have gratuitously given the Earth an appearance of age, and species the appearance of evolution, for no apparent reason except to screw with scientists, then that's omphalism.