A while ago, in this blog post, I mused about what the earth would be like with no moon. You may hear the Moon blamed for things as diverse as reproductive cycles and people’s moods, but in that post, I argued that if all of a sudden, we’d find ourselves without a moon, not a great deal would change. The Sun causes tides, albeit smaller ones, and any stability issues of the Earth’s axis would not change overnight.
But this is not a realistic scenario. The Moon isn’t going to just disappear (the subject of Death Star-like blasting a planet apart is a subject for another blog post, but let’s just say it’s physically nigh impossible). The real question I should have asked is: what would life on Earth be like if Earth had never had a moon? If the Pluto-sized object that may or may not have collided with us to form the Earth and Moon as we know them had missed the Earth, and sailed straight on, to eventually burn up in the Sun.
The situation would look vastly different. The Earth-Moon system is vastly different from other known planets in terms of relative size. Only the largest moons of Saturn and Jupiter are similar in size to our Moon, but those planets are of course much more massive. The Earth-Moon system could well be referred to as a double planet. Of course Earth and Moon affect each other, and this influence comes in the form of gravity. While the gravity of the Moon affects all surfaces of the Earth equally, it’s only the oceans that can react to this gravity. Yeah, that’s how the tides are formed.
Imagine the Earth as an oblong bubble of water, with bulges both on the side where the Moon is at and the opposite side. This bulge orbits the Earth at the rate the Moon does. But the Earth itself rotates inside this envelope of water, and this creates friction at the place where water and solid surface meet. In effect, the water is forever trying to keep up with the planet. Friction creates warmth, and yes, loss of speed.
So it is that over the four-plus billion years of the Earth’s lifetime, the rotation speed of the Earth has slowed from an eight-hour day to our current twenty-four hours. Is still slowing, in fact.
Of course life on a planet with days of eight hours would be very different. We’d experience vastly more powerful weather and especially wind systems. With a rotation speed like that, there would probably not be much opportunity for much North-South weather movement, but we’d have strong bands of air movement, much like Jupiter (which has a daylength of ten hours). We’d have similar ever-lasting cyclonic systems.
And what would it do to the seashores, having the tides jump up twice in eight hours?
Or to the biology of animals evolving with that kind of daylength? Would we all have nervous tics from seeing the Sun whizz by?