What would be the effects of Earth not having a moon?

[vincentm]

What would be the effects of Earth not having a moon? I know that our moon is slowly drifting away. But what would happen then?

 

[Tropo]

The moon provides a stabilizing influence on the Earth's axial tilt (obliquity). With the moon in place where it is, our tilt, which is currently at 23.5°, moves between only 21.5 and 24.5° about every 41,000 years. This cycle used to be in synch with ice ages, but it hasn't been for the past million years or so.

Without the moon in place, our tilt would vary much more, maybe to extremes of 60° or more. Mars does this since its moons are too small to stabilize the planet's tilt. This could cause extreme climate swings and big-time ice ages.

There have been arguments that, without our moon, life on Earth would not be possible, but I think that's a little over the top myself.

 

[Entropy]

There have been arguments that, without our moon, life on Earth would not be possible, but I think that's a little over the top myself.

Well, I think complex life would have a hard time getting a foot hold.

 

[Tropo]

I guess your name fits!

 

[Ophiolite]

Tides would be significantly reduced. This could have had important implications for the emergence of terrestrial life had there been no moon.
The 'day' would be much less than twenty four hours long. A substantial part of the reduction in day length is a consequence of the tidal interaction of the Earth and the moon.
There would be an increased risk of being struck by a large bolide: a proportion of these are intercepted by the moon.
The absence of eclipses might have delayed the early development of astronomy.
Romantic songwriters would have been lyrically challenged.

 

[marcus]

A substantial part of the reduction in day length is a consequence of the tidal interaction of the Earth and the moon.
.

could say a subtantial part of the reduction of rotation rate is due to tidal drag
(reducing the reciprocal of day-length same as lengthening day)
this was probably intended, consistent with what else you said

good summary, also like what tropo said about stabilizing the axis, so seasons and iceages not so extreme, and what entropy said about that helping complex multicell critters evolve

this is a neat thread, thanks vincent for posing an interesting question.


I don't think the moon is drifting away fast enough to worry about,
does anyone remember an estimate about that?
intelligent life, once evolved, could probably cope with more radical tilt of the axis, and even slightly more bolides. and so could get along with much more distant moon (or none at all)

but the moon sure seems to have helped life succeed EARLY ON

 

[EnumaElish]

Are planets also drifting away from the sun, or are they getting nearer to it? (I am under the impression that the latter is true.)

I forgot what made the moon fall to Earth in H.G. Wells' Time Machine.

 

[JesseM]

I forgot what made the moon fall to Earth in H.G. Wells' Time Machine.

It didn't in the original H.G. Wells book, it was only the 2002 Time Machine movie where the moon blew up...the explanation they gave there was that people were using nuclear bombs as part of mining operations on the moon.

 

[JesseM]

I don't think the moon is drifting away fast enough to worry about,
does anyone remember an estimate about that?

According to this, it's drifting away at about 4 cm per year, and billions of years in the future it will stop drifting away when the length of the Earth's day is the same as the length of the moon's orbit (around 47 modern days), at which point the moon will be about 1.35 times as far away as it is now.

 

[EnumaElish]

It didn't in the original H.G. Wells book, it was only the 2002 Time Machine movie where the moon blew up...the explanation they gave there was that people were using nuclear bombs as part of mining operations on the moon.

Oh, I hope life will not imitate art in this case!

 

[EnumaElish]

According to this, it's drifting away at about 4 cm per year, and billions of years in the future it will stop drifting away when the length of the Earth's day is the same as the length of the moon's orbit (around 47 modern days), at which point the moon will be about 1.35 times as far away as it is now.

And what is the reason for the day stretching to 47 times its current length?

 

[JesseM]

And what is the reason for the day stretching to 47 times its current length?

According to the page, the drifting away of the moon is related to the slowing of the rotation of the Earth because of "tidal friction", which transfers the Earth's rotational momentum to the moon's orbital momentum. http://curious.astro.cornell.edu/question.php?number=124 gives a slightly more detailed explanation of how tidal friction works:

The reason for the increase is that the Moon raises tides on the Earth. Because the side of the Earth that faces the Moon is closer, it feels a stronger pull of gravity than the center of the Earth. Similarly, the part of the Earth facing away from the Moon feels less gravity than the center of the Earth. This effect stretches the Earth a bit, making it a little bit oblong. We call the parts that stick out "tidal bulges." The actual solid body of the Earth is distorted a few centimeters, but the most noticable effect is the tides raised on the ocean.

Now, all mass exerts a gravitational force, and the tidal bulges on the Earth exert a gravitational pull on the Moon. Because the Earth rotates faster (once every 24 hours) than the Moon orbits (once every 27.3 days) the bulge tries to "speed up" the Moon, and pull it ahead in its orbit. The Moon is also pulling back on the tidal bulge of the Earth, slowing the Earth's rotation. Tidal friction, caused by the movement of the tidal bulge around the Earth, takes energy out of the Earth and puts it into the Moon's orbit, making the Moon's orbit bigger (but, a bit pardoxically, the Moon actually moves slower!).

The Earth's rotation is slowing down because of this. One hundred years from now, the day will be 2 milliseconds longer than it is now.

 

[Chronos]

Tidal locking is the name of the game. The moon is already tidally locked to Earth [i.e., not rotating with respect to the Earth's axis]. The Earth will become tidally locked with the moon in the distant future, as JesseM noted. It will take Earth much longer to become tidally locked to the moon due to its much greater mass, oceans and denser atmosphere

 

[marcus]

According to http://www.physlink.com/Education/AskExperts/ae429.cfm , it's drifting away at about 4 cm per year, and billions of years in the future it will stop drifting away when the length of the Earth's day is the same as the length of the moon's orbit (around 47 modern days), at which point the moon will be about 1.35 times as far away as it is now.

Thanks Jesse!
this incidentally confirms the point Chronos made

I will put down an attempted explanation and then check the link to see if it agrees
basic principles are conservation of angular momentum, and friction

the total angular momentum represented by moon orbit PLUS rotation of Earth cannot change (system approximately isolated, nothing to take it up)

so if Earth rotation slows down from friction with the tidal bulge
then it loses spin, and the moon orbit has to gain it----by having orbit radius extend

===================
yes, I checked Jesse's link and at least my explanation is consistent with it.

the way I picture it is the tidal bulge tries to keep pointing at the moon (two bulges aligned with the earthmoon line)

and the solid Earth is rotating UNDER that bulge, and by friction of the water having to flow around obstacles etc, the solid Earth pulls the bulge around so that instead of being exactly aligned it is just a little bit IN ADVANCE of the moon

now that bulge is dragging the moon ahead, like when you whirl something tied to the end of a string, and to put energy into the whirling you make your hand just slightly LEAD the object, so your hand is slightly in advance of the object and the string is not only holding the object inwards but also dragging it ahead.

so that puts some energy into the moon's orbit (there is also energy lost by the turbulence of the flowing water which just heats the water slightly, we don't have a simple energy conservation here because some leaks off)

and the way a roughly circular satellite orbit absorbs energy is gets a longer radius, goes a little bit slower, with a longer period, and has an increase in angular momentum.

so Jesse's link says this has to keep happening, with the moon getting farther and farther away, UNTIL the Earth is no longer rotating faster than the moon is orbiting (until Day = Month) so that friction is no longer dragging the bulge ahead-----and then the tidal bulge will be perfectly aligned with the earthmoon line and will no longer be in advance, so no further transfer of energy.
=========================

OOPS AND SHUCKS
I just looked at jesse's OTHER link
http://curious.astro.cornell.edu/question.php?number=124
and see that it says essentially the same as I just wrote so I didnt need to add the explanation.