Get a life II
Improbable outcome if we consider that the relative mass of the parent bodies, and the speed and angle of the collision had to match within a narrow margin to emerge as a stable system as this. Yet, one of the latest cries in Planetary Science is the convincing evidence Pluto and Charon, its moon, underwent a similar episode. Charon is to Pluto more or less as the Moon is to Earth in matters of relative size. That this type of episode happened twice in a single planetary system may point to the fact it is not that much improbable, but then again this may be highly unlikely yet not impossible.
Whatever, the Pluto issue is out of scope, the important thing to note is the Earth has a comparatively large satellite and this is uncommon. And very important, too.
The large moon has first of all a stabilizing effect on the Earth's rotational axis. Were it not for our natural satellite, this axis should wobble erratically, playing an equally erratic role on the distribution of climatic zones on short-term scales.
Think, for example, on Hawaii turning into the South Pole in as little as a couple of million years, and so on.
Climatic long-term stability is paramount for the emergence and evolution of delicate primitive life forms, something that lasted for about four billion years until more complex and resilient organisms had a chance to develop.
No less important is an effect we experience twice each moon cycle - currently about 28 days. Tides are in great part due to the Moon's gravitational influence, and tides promote the formation along rock and sand shorelines of temporary pools. It is believed the first bacteriae appeared in those tidal pools by a process we still don't know in detail, yet we are fairly certain was favored by them. In a way, the Moon pumped life to jump start.
Home at last
Picky prospects as we are, we went through a long search for the perfect nesting site. Discarding most of what the Milky Way had to offer as primitive or crowded or violent, discarding most planetary systems for too large bully planets close in, too cold or too hot places, too short the time available to settle comfortably, whatever.
But we found in the end a right sized planet with the right mix of matter from which to assemble complex molecules, with plenty of liquid water to mix and
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