Earth is strange - a billion years of water and chemistry on every grain of sand on every beach. Every combination of temperature, sunlight, wetting and drying as tides slosh things around in every phase.

It's like a bioreactor for creating life. One could argue, it's highly unlikely given all those experiments and all that time, that life would avoid being created.

And Mars? It has a moon too, two of them. Tides as well, lunar and solar. Pretty much the same deal.