“What was most significant about the lunar voyage was not that men set foot on the Moon, but that they set eye on the Earth.” -Norman Cousins

What would life on Earth be like without the Moon?

Our nearest neighboring body in the cosmos has a profound effect on us. It’s helped not only shape our evolution, biologically, but has shaped the entire evolution of our planet. Created some 4.5 billion years ago — when our planet and Solar System were still in their infancy — when a roughly Mars-sized planetoid crashed into a young proto-Earth, the Moon has been our companion-in-orbit ever since.

Image credit: Fahad Sulehria of http://www.novacelestia.com/.

Image credit: Fahad Sulehria of http://www.novacelestia.com/.

It’s totally reasonable and conceivable that life would have sprouted and thrived on Earth even without the Moon, but things would be significantly different in detail. Some of them would be obvious, some would be a little more subtle, but there would be a great many impacts that we’d notice if we knew to look for them.

So today, I present to you the top 5 things we’d miss if we didn’t have a Moon! (And no, “landing on the Moon” didn’t make the list!)

Image credit: Wadsworth Publishing / ITP (L), Sagredo, via Bob King (R).

Image credit: Wadsworth Publishing / ITP (L), Sagredo, via Bob King (R).

1.) There’d be no such thing as eclipses on Earth.

Without the Sun, Moon and Earth, there would be no eclipses. The Sun is constantly shining on Earth, casting a shadow for over a million miles (and over a million kilometers) in its wake. Yet without our Moon — just a few hundred thousand miles (or kilometers) away — there’d be no object that would pass through the Earth’s shadow; there’d be no lunar eclipses.

There’d also be no solar eclipses: no annular, partial, or total eclipses. The Moon’s shadow is almost exactly equal in length to the Earth-Moon distance; without the Moon, no shadow, and no disc to block the Sun’s disk. The next largest object that can pass in between the Earth (after the Moon) is Venus, and while it’s incredibly cool when that happens, that’s the closest we’d get to an eclipse without the Moon.

Image credit: © 2002 By Keith Cooley, via http://home.hiwaay.net/~krcool/.

Image credit: © 2002 By Keith Cooley, via http://home.hiwaay.net/~krcool/.

2.) Our tides would be tiny in comparison to what they are now, and they’d be dominated by the Sun.

Although the Sun is some 400 times larger (in diameter) than the Moon, it’s also, on average, about 400 times farther away. This explains why they appear about the same angular size from Earth. But the Sun is only about 27 million times as massive as the Moon.

Why in the world would I say “only” there? Because it would have to be about (400)3 times the mass of the Moon, or 64 million times its mass, in order to have the same effect on Earth’s tides as our small, lunar neighbor. As it stands, tides from the Sun are only about 40% as strong as tides from the Moon. When the Sun and Moon line up in either the “new” or “full” Moon phases, we get spring tides, 140% as large as a typical tide, and when they’re at right angles, we get neap tides, only 60% as strong as a standard tide.

Image credit: Arthur Thomas Dodson of Bridgeport, Connecticut, via Wikipedia.

Image credit: Arthur Thomas Dodson of Bridgeport, Connecticut, via Wikipedia.

But without any Moon at all, our tide patterns would be much simpler, and only the Sun would contribute anything substantial. So our tides would only be about 40% as large as a typical tide is today. Not the biggest of deals, but definitely something we’d notice.

But there’d be some very large impacts on how we experienced life on Earth.

Image credit: user Rutjuga of the forums at http://www.defence.pk/.

Image credit: user Rutjuga of the forums at http://www.defence.pk/.

3.) Nights would be much, much darker than we’re used to.

If you’ve ever been outside in the wilderness on a totally moonless night, without any artificial light, you probably noticed two things. First, the night sky is absolutely breathtaking; you can see thousands upon thousands of stars, the plane of the Milky Way, and even dozens of extended, deep-sky objects with your naked eye alone. And second, you can’t see a damned thing in front of your own face.

Image credit: Paul Kinzer of Cambridge University Press.

Image credit: Paul Kinzer of Cambridge University Press.

The Sun is much, much brighter than the Moon; the full Moon is just 1/400,000th as bright as the daylight Sun. Yet Venus, the next brightest object in the night sky, is only 1/14,000th as bright as the full Moon!

We have pretty decent night vision, so long as the Moon is out. But without it, our night vision is, well, not very effective, as anyone who’s been camping without a headlamp or working flashlight can testify. It’s probably safe to say that vision would have evolved somewhat differently without the Moon, and that our nights would provide us with a wildly different world to experience.

But that wouldn’t be the biggest difference, not by a long shot.

Image credit: Tim Thompson.

Image credit: Tim Thompson.

4.) A day on Earth would be much, much shorter; only about 6-to-8 hours, meaning there’d be between about 1,100-1,400 days in a year!

Our 24-hour-days may seem like they don’t change from one year to the next. In reality, the change is so tiny that it took centuries to perceive, but the Earth’s rotation slows down ever so slightly over time, thanks to the tidal friction provided by the Moon. The slow-down is very, very slow (on the order of microseconds-per-year), but over millions and even billions of years, it adds up!

In about 4 million years, we’ll no longer need leap years to keep our calendars on track. If the Sun would live an infinite amount of time, the Earth would eventually slow down and become tidally locked to the Moon, the same way the Moon is locked to us and always shows us the same face. Instead of 24 hours, a day would last for some 47 current Earth days. (In reality, the Sun will end its life long before that happens, so no worries there.)

But in the meanwhile, we can use what we know to extrapolate backwards in time, and we find that in order to get a 24 hour day today, the Earth had to have been spinning much faster in the past: about three-to-four times as fast more than four billion years ago! If we didn’t have a Moon — if we never had our Moon — the day would be much, much shorter than it is today, and our planet would have a larger equatorial bulge, much more flattened poles, and over 1,000 days in a year!

And finally…

Image credit: Center for Mars Exploration, via http://cmex.ihmc.us/.

Image credit: Center for Mars Exploration, via http://cmex.ihmc.us/.

5.) Our axial tilt would vary tremendously over time!

You probably learned that the Earth rotates on its axis, tilted at about 23.5 degrees relative to its orbital plane around the Sun. This is true! But did you ever stop to think what keeps the Earth from changing the tilt of its axis-of-rotation? The same way a spinning top not only precesses but also exhibits more complicated motion over time (some of which you may know as nutation), an entire planet can do this, too. Mars is a perfect example: currently tilted at about 24 degrees relative to the Sun, we know that its axial tilt varies from about 15 degrees to about 35 degrees over time!

Earth is special, though, because we have an external force to stabilize us against that sort of behavior. Know what’s responsible?

Image credit: Mathieu Dumberry of http://www.ualberta.ca/.

Image credit: Mathieu Dumberry of http://www.ualberta.ca/.

That’s right, the Moon! Thanks to our Moon, our axis stays tilted between 23 and 26 degrees over time, even over hundreds of millions of years! But without our Moon, there would be nothing preventing catastrophic shifts in our rotational axis. It’s probable that sometimes, we’d be like the planet Mercury, orbiting in the same plane as our rotation, and having practically no seasons due to our axial tilt. At other times, we’d possibly be as extreme as Uranus, rotating on our side like a barrel, having the most extreme seasons imaginable!

So the next time you take our Moon for granted, think about how different life would be — and how different the entire history of life on Earth would have been — if we didn’t have our Moon!

Comments

  1. #1 Jnecolong
    Georgia USA
    August 8, 2013

    If our tides had been much smaller. Life in our oceans would have had to have been much smaller. General mathematics.

  2. #2 Jnecolong
    August 8, 2013

    Life began in the ocean. Elements,Minerals electrical exchange motion=life! Actually complete mathematical perfection. Until our wonderful egos stepped in. Pollution, war.

  3. #3 Paweł Zuzelski
    Zurich
    August 8, 2013

    Ethan, sorry for asking the same question again… But you wrote some time ago, that our Moon can’t lock the Earth, because the Sun is much more powerful…

    Excellent article, as always, thanks!

  4. #4 Michael Kelsey
    SLAC National Accelerator Laboratory
    August 8, 2013

    @Jnecolong — Citations, please, for your unsupported pseudo-poetic assertions?

    Tidal motion is extremely variable, and dependent primarily on the details of coastal shape (compare the Bay of Fundy to Cape Cod, for example).

    The “size of life” is a content-free phrase. Are you discussing the sizes of bacteria, protists, Vendian forms, modern plants, or multicellular animals? The latter range over roughly six orders of magnitude size. How exactly does that correlate to tidal motion?

  5. #5 Michael Fisher
    https://secure.gravatar.com/michaeljfisher
    August 9, 2013

    This is just speculative since I’m just a layman, but how about this for your list?

    6.) No Plate Tectonics
    If the moon-creating collision had never occurred the Earth’s outer crust would have been thicker & we wouldn’t have had plate tectonics. This would have led to increased, massive volcanism to shed heat like on Venus or the massive stacked volcanoes of Mars. Erosion would flatten all high spots with only volcanoes to rebuild mountains & thus we would end up with mainly a water world

    7.) Different Atmosphere
    I’m unsure about this… Suppose there was carbon-based life on Earth despite the lack of plate tectonics in 6.) above. The carbon cycle would have a much smaller throughput which would lead to a greenhouse effect like Venus.

  6. #6 Michael Fisher
    https://secure.gravatar.com/michaeljfisher
    August 9, 2013

    7.) Smaller Magnetic Field Sooner
    I read somewhere that plate tectonics effects the molten outer crust. No plate tectonics would lead to a reduced or zero magnetic field much sooner in Earth’s history. The mechanism wasn’t explained in the article so I have some doubts about this.

  7. #7 Andrew Dodds
    August 9, 2013

    Michael Fisher -

    There is speculation that without the Moon-forming event, we would have a much smaller Iron core and hence no magnetic field – we’d be more like Venus.

    Why Venus has a different tectonic style to Earth is something of a mystery (or was when I last looked).

  8. #8 Wow
    August 9, 2013

    “But in the meanwhile, we can use what we know to extrapolate backwards in time, and we find that in order to get a 24 hour day today, the Earth had to have been spinning much faster in the past: about three-to-four times as fast more than four billion years ago”

    The validity of such extrapolation to 4 billion years ago is questionable, though.

    “The Earth four billion years ago may have had an eight-hour day” would be more apt.

  9. #9 Sherrick
    Edmond, OK
    August 9, 2013

    Another effect is the shield that the moon provides us with. How many large rocks would have hit the Earth that instead hit the moon. Extinction events would be more common.

  10. #10 Alan D McIntire
    August 9, 2013

    I noticed how bright a full moon was, and how dark it is without a moon while on my uncle’s farm during the summer.

    I suspect that the fable of crazies, thieves, etc. coming out on a full moon originated before there was electric lighting. Nowadays, with city lighting at night, and flashlights and headlights available at night, the moon should have no effect, but pre electricity someone up to no good could operate most effectively when the moon was close to full.

  11. #11 Cleon Teunissen
    August 9, 2013

    About the Earth axial tilt variation with or without the Moon.

    It’s counter-intuitive. I would readily believe the opposite, that in general the presence of a large moon would make things _less_ stable.

    Let me recapitulate the difficulties, as I understand them.
    The effects are very subtle. In a sense the dynamics is not understood.

    Researchers design computer-models, those models are run multiple times, with slightly different starting conditions.
    If the system remains stable in all of the runs then that’s a good indication the system is inherently stable. If there are significant excursions in some or all of the runs then apparently the system is not stable.

    So the point is that the information that is obtained from the runs is statistical only. There is good reason to trust the outcomes, but the research does not offer a window on _why_ the presence of the Moon makes a difference.

    I came across an article published in 2011. The authors report that while they found a with-moon and no-moon difference, the difference was small.

    They did see some large tilts in some of the runs, but the tilt always changed so slowly that it would not interfere with life on the planet.

    http://barnesos.net/publications/papers/2012.01.Icarus.Barnes.Moonless.Earth.pdf

  12. #12 Wow
    August 9, 2013

    The earth, like any spinning object, is not entirely a sphere but an oblate spheroid. That means that if the tilt of the axis of rotation moves, then the equatorial bulge will move and this will affect the gravitational field felt by another object in space, the closer the more it is felt.

    E.g. the moon.

    That would cause a force on the moon which doesn’t WANT to be moved and the reaction will dampen out the movement of the earth.

  13. #13 Jesse
    August 9, 2013

    Stephen Baxter wrote up an interesting bit on the Earth minus a moon. A few things he said might happen:

    – less tidal mixing, so there would be very different biota. The gas and chemical exchange would be dominated by runoff.

    – faster winds (since the planet would rotate faster). Stronger storms, an atmosphere much more like a Jupiter in its dynamics. (Obviously it wouldn’t be exactly like, but the wind pattern would be similar).

    – A higher CO2 level in the atmosphere, more like Mars or Venus. Note that most terrestrial planets have CO2 as the dominant atmospheric gas. Even Europa has that, though it’s mighty thin. Titan is the only major exception I can think of.

  14. [...] at Scienceblogs offers five things the Moon does for us, including one we mightn’t have considered, [...]

  15. #15 Bert Wells
    August 9, 2013

    Great post. One thing left out though: the Moon has been slowly moving away from us. Around the time that life first formed, the Moon was in a very close orbit, and the tides were HUGE. Some estimates of over a thousand feet(!)).

    It is speculated that the mixing of solids into the early ocean from the enormous tides played a significant role in early oceanic geochemistry that produced life.

    Imagine standing on mountain by the sea, and watching a thousand foot tide come in!

  16. #16 Bob Dowling
    August 11, 2013

    What would the period of the nutation be? Can we estimate an order of magnitude?

  17. #17 trent
    urbana
    August 12, 2013

    Wouldn’t there be no life

  18. #18 Sean T
    August 13, 2013

    I’m not sure why there’d be no life without the moon. I’m guessing you are thinking of the role of tidal pools in abiogenesis, but I’m not sure that there’s solid evidence that this is where life actually formed. If life formed in the oceans (such as in thermal vents, for instance) lack of a moon would have no effect.

    I am sure, though, that lacking a moon, the intertidal habitat would have been affected. This would likely have led to differences in how species evolved, and we likely would see different types of species than we actually do.

  19. #19 Wow
    August 13, 2013

    Life would have a lot of problems lasting stably for long enough to evolve as far as what the-man-in-the-street would call life.

    You may be thinking “bacteria and self-assembling virii” as “life” and others thinking “something you can point to and go ‘that’s a living organism’”.

  20. #20 SimonG
    UK
    August 13, 2013

    Another good read on this topic is Isaac Asimov’s “The Tragedy of the Moon”.

  21. #21 Sean T
    August 15, 2013

    Fair enough, Wow, but while I’m no expert on biology, I have taken a couple of courses. In all of them, we did deal with kingdom prokaryota. If the poster meant multicellular life, he should have stated that.

  22. #22 Wow
    August 15, 2013

    It isn’t about how much biology you know, but what you’d consider life to be life when you are looking for somewhere to lay your hat.

    A planet occupied by bacteria and amoeba may be a worry for infectious disease vectors, but we wouldn’t say “we have to move on because this planet is inhabited”, would we.

    But if something were there that appeared to us to be a macro-scale animal comensurate with, say, a dog or dolphin, we may well decide that it is already occupied.

    The difference not being how many cells it has, but as to whether we can morally take the planet over.

    “It has single celled life” is *scientifically* a huge thing to know.

    “it has single celled life” is for the future of mankind, damn pointless.

  23. #23 Tanya Dax
    Florida
    August 17, 2013

    I’m curious about this 8 hour day without the Moon. You get this figure by projecting backwards from the current rotation rate and the steadily changing Earth-Moon distance. My problem with this method is that the Earth-Moon system was created in a collision event, which must have imparted some change in rotation to the proto-Earth. So, in truth, do we not know the initial condition of the system? Of course, I’ve seen some excellent models of the collision. Maybe those experts have not only projected back the current motion, but also have done the math for the collision.

    Ha, maybe *I* should do some more reading and satisfy my own curiosity.

  24. #24 ppzpzpp
    August 20, 2013

    Hi,

    “In about 4 million years” – would “billions” be more correct?

  25. #25 Norris Preyer
    August 23, 2013

    I don’t think I understand the comment about the Earth’s axis of rotation precessing about — shouldn’t the angular momentum of the Earth be conserved?

  26. #26 Wow
    August 24, 2013

    It is. Precession is another rotation.

    Throw a ruler up in the air and watch the longitudinal spin change to axial spin.

  27. [...] The top 5 things we’d miss if we didn’t have a Moon [Starts With A Bang] (scienceblogs.com) [...]

  28. […] making waves possible, which is a great thing. “What would life on Earth be like without the Moon?” well for one it would cause us to have darker nights then we are used to, because without […]

  29. #29 Lyn Lowry
    Queensland Australia
    April 2, 2014

    Just two comments from me, a member of our planet. 1. The Moon – Please keep off. If everything science says is true then we should leave our moon alone for us to survive.
    2. There is a very good chance that other planets with moons have some life forms also.

  30. #30 taylor
    25705
    April 7, 2014

    you guys didn’t help at all.

  31. #31 taylor
    April 7, 2014

    sorry

  32. #32 taylor
    April 7, 2014

    im kidding you guys did help

  33. […] controls much more of our experience on earth than we sometimes think about, and without it things would be very different here. And now that I’ve sneakily slipped in several info links about the moon (because it’s so cool […]

  34. […] Without the moon: […]

  35. #35 Moon Good Night
    June 30, 2014

    […] Sources: BBC Cornell Astrobiology Magazine Universe Today Astronomy Today Science Blogs […]