In other words – why is the Moon important for the development of life on Earth?
The most obvious reason lies in tides – the rise and fall effect of sea level. This happens due to the Moon – its gravitational pull shapes the Earth in an oval shape. How is this important to life? Well, in the areas where tides are evident on the landscape – such as seashores – the retreating and returning of sea water is pretty much changing it from one ecological niche to another. This happens over the space of a few hours, and creates a very unique environment.
This allows for life in one niche experience the conditions of the other, while returning to its home environment. Over time, and due to evolution, living things that are initially sea-dwelling, could become amphibious. It’s life spreading from one niche to an other (e.g. from the oceans to land).
A long long, LONG time ago the Moon used to be closer to the Earth – meaning that these effects would have been more evident. Furthermore, if its gravitational pull would become aligned with that of the Sun, then there would be tidal effects on solid landmass! Giving rise to intense deformation and radioactive elements… which may have enhanced the melting of Earth’s surface and helped initiating plate tectonics (a reason why there’s life on Earth!). It sounds horrible, but actually such an event could help shape a lifeless rock into a dynamic planet (Earth). How? Well, it would give the much needed heat loss (the Earth was too hot for us to handle then), boost land surface production (through things sticking out in the ocean), promote new life forms and, eventually, the biodiversity that we enjoy today 🙂
But that’s not all.
One theory suggests that the Moon was formed after a Mars-sized planetesimal (small planet) stuck the Earth and blew off a big chunk. This would have eventually accumulated into a spherical shape. At the same time the Moon was forming, the Earth enjoyed some changes of its own. Pretty much, there would have been a reforming of the Earth, new and improved, with a molten rock outer layer – called the mantle (hundreds of kilometers thick where the convection of plate tectonics takes place). Thus, Moon equals plate tectonics, sort of.
(The lunar rocks collected on missions, and calculations that the Moon is gradually moving away from the Earth strongly support this theory.)
That’s still not all.
This even would have sped up Earth’s rotation (simple physics – something hits something on the side and makes it spin faster), giving us our short 24h days. And the tile of the Earth’s spinning axis was changed to the present 23.5° (responsible for seasons – another pretty cool thing). Not only that, afterwards, the Moons pull could have helped stabilize the tilt of the Earth, without which the Earth would suffer extreme changes in surface conditions thru the amount of sunlight places get. Without that we’d be pretty much like Mars, cold where there’s sun, and uber-cold where there isn’t (and for really long times).
So, for today’s Earth, the tilt allows for varied, but sensible, climates to support life. Next time you curse the moon for shining in your face while you try to sleep and making the neighborhood dogs go nuts at night – think back and realize that without it you’d be a Martian.
P.S. Boring stuff:
At a less obvious glance, the lack of metal on lunar samples and the abundance in deposits at the surface of Earth suggests that the collision between the proto-Earth and a Mars-sized planetesimal let some of the Earths metallic inner core spill outwards onto the top layers and the mantle where it would later emerge under plate tectonics within the reach of developing, intelligent, technological civilization.