moon is a remnant of young earth colliding with its twin planet, part of it was absorbed into earth (that's why we have so much iron & melted dynamic core, which btw generates strong magnetic shield protecting us from sun's solar winds). Rest formed moon over time, which is unusually big compared to its parent planet and unusually close (all those stabilizing influences + tides). If we haven't had moon, earth would be "wobbling" on its path around sun frequently, causing very frequent glacial ages.

Necessary for life itself? Never said that. Stromatolites and similar single cell organism can survive about anything short of earth being consumed by black hole. Necessary for evolution of complex life and its explosion in variety that we see today, and more importantly our society? I personally do believe so. Just watch the document and then we can discuss.