The Earth, Moon, Tides, Orbital Paths, Life....... heck, everything.

Factual Questions
1

Sure was a clear sky out the other night. I could see the moon. A sliver was lit but I could see it all, against the deeper inky blackness of space. I tell you, it gets a Doper wondering.

If the moon rotated around the earth in a perfect path, there would be no tidal force on the planet that would affect the oceans. Right? If there were no tidal forces on the oceans, would life still have evolved the same way it did? ( For the sake of this G.Q., since this ain’t G.D., please allow the thread to stand on the supposition that life emerged from a primordial soup/ocean mass billions of years ago. ).

Is it possible that something as random as the path followed by the moon would have had enough affect on the earth’s oceans as to alter the development of life? I am feeling that the tides literally had something to do with the emergence of life. I am wondering if ocean masses that more or less are standing water masses on other planets would develop or sustain life in the same way? Because of the tidal forces, materials from extremely deep out in the oceans eventually wind up being tossed up on the shorelines.

How would a lack of tidal forces contribute to a lack of development of life on earth? Were the tidal forces that existed billions of years ago ( and of course, still do now ) a key element in this process?

And, to plug in the Everything portion of my question, what the heck are the odds that the S.E.T.I. folks will ever find a combination of planetary masses, forces and raw materials anywhere else that have produced the exact results needed for not only life, but advanced life to develop?

Here, let me freshen up that cup of coffee. You’re going to need it. :smiley:

** For the sake of the factual portions of my O.P., let’s see if this can survive in G.Q. before it gets shuffled off to G.D. **

Cartooniverse

2

There is an equation to calculate the probability of intelligent life existing in the universe, it is as follows:

Quoted from here though I don’t believe they created the equation. The difficulty of such an equation is that it still involves a lot of guess work, especially on the factors L and fl. I have only ever seen one attempt to come up with an ultimate answer using this equation and it somewhat conveniently came up as 1, that 1 civilisation being us, all rather too convenient for me. IIRC they used 1,000 years as the approximate lifetime of a civilisation, that is before they either use up all of the available resources and destroying their planet or end up killing each other due to technology becoming so advanced that it becomes “easy” for just about anyone to kill everyone else.

I’m not 100% sure what MWG stands for in this context, a best guess would be “Milky Way Galaxy”.

I’m not sure what the point of the SETI program is, even if we do recieve and decode a message from the depths of space saying “Hello, anybody out there?” we lack the technology to respond in a timely manner. I suppose it would solve the question of whether we are alone or not but we couldn’t really communicate.

3

Wrong.

We get tides because the side of the Earth that’s furthest from the Moon “wants” to orbit the Moon slower than the side that’s nearest, but is forced, because the Earth is one big lump, to orbit it at the same speed, or a little faster. But the oceans are able to deform to try to follow the path they “want” to.

(I know it sounds odd to talk of the Earth orbiting the Moon, but in simple terms that is what tides are down to.)

Whether the Moon orbits in a circle or ellipse doesn’t greatly affect this. Mind you, it’s damn nearly impossible for the Moon to settle into a circular path. An ellipse is self-correcting - as the Moon gets nearer, it speeds up, so it moves out, so it slows down, so it gets nearer…

Probably not. It’s a fair guess that pools of water left stranded by the tide provided a niche where it was an advantage to be able to survive in shallow water, and eventually in no water at all.

The odds? No data. We know of one world in the entire universe where it has happened. That’s not enough to extrapolate from.

4

I thought tides were caused by the gravity of the moon “squeezing” Earth. Since water is free to move it rises in the areas where the Earth is squeezed lower. Or something like that.

Any physicists that can tell me where I’m mistaken, as I surely am.

5

It’s more just that the oceans are freer to move under the influence of the moon. So they end up pulled into a sort of egg shape, which surrounds the more spherical rock beneath.

6

The simple explanation is that the side of the Earth facing the Moon gets pulled more than the middle, which gets pulled more than the far side. The planet itself can’t deform, but the oceans can. However, this simple answer is what’s called a “lie to children”, a bit like Newton’s theory of gravity or the Bohr model of the atom. What I said above about orbits is closer to the truth.

Time to page the Bad Astronomer, methinks.

7

I think you’re saying that the Earth’s crust gets squashed somewhat, and the water rushes in to make the Earth spherical again, making the water level with respect to the land be higher.

That’s not right.

Think of it this way. If the Earth always had the same side towards the Moon, the Earth would attain an elliptical shape, with the longer axis pointed towards the Moon. Since the Earth is spinning and the solid part (the crust) can’t bend quickly, it stays pretty much circular, but the oceans, which can move much more easily, come in to fill out that elliptical shape. So the overall shape of the oceans is elliptical at any time, but the ellipse is always having to move with respect to the land mass because the land mass is spinning.

8

I’ve thought about the effect of tides on evolution for a few decades now. (Well, not continuously or even that frequently.) I only recall two times where the possible impact of the moon was discussed, and I can’t recall the sources or specifics. I do recall that one said that it was inevitable for swimming critters to eventually make use of the land niche, so the moon was not necessary. The other article mentioned that the moon was necessary, but sadly I did not keep a copy. Unfortunately my answer thus far isn’t very good for factual GQ. Basically, from what I have come across, it is not thought of much and the opinions are split. Granted, I have not read any recent textbooks or scientific articles dealing the subject. The articles are what I came across in general reading. As this is a subject that interests me, I hope I will be forgiven for blabbing on about further thought better suited for GD.

My personal speculation is that our oversized moon assisted in the evolutionary process. Firstly, I wonder how common or unique it is for a rocky planet, as opposed to a larger Jupiter-type planet, to have a satellite that is a significant percentage of the size of the main planet. From my limited understanding of planetary formation, I believe that the earth having a satellite the size of the moon, big enough to affect tides even, is rather unexpected. I would expect that the action of swimming critters periodically being trapped in tidal pools would have created an evolutionary push towards critters that could scamper across land enough to get back to the comfortable ocean. It is my belief that the tide producing moon advanced the evolutionary process by a huge degree, perhaps by orders of magnitude. For my own belief, I manage to fit God into the equation, although one with a strange sense of humor and who would offend mainstream religious groups. (Consider eclipses. That has to be more than a grand Cosmic Coincidence. To me it is proof of a God with a quirky sense of humor. However, there is no requirement for anyone else to hold the same belief.)

As for life elsewhere, well that is, of course, still in the realm of speculation. The universe is so huge (I can’t recall the proper HHGttG phrasing) that I’m sure that of the billons of stars in each galaxy and the billions of years galaxies have been around, in all probability there are at least one or two (or dozens?) of sentient life forms that develop in each galaxy. It is sadly unlikely that we will ever come across any of them though (IMHO). How does the quote go? As unlikely as it is that there is intelligent life somewhere else in the universe, it is even more unlikely that we are totally alone. Something like that.

9

As stated above there are several ways to look at tides. The key is understanding that gravitational force decreases with distance, so the effect of lunar gravity depends on how far you are from the moon, which depends on which side of the earth you are swimming on.

The tidal forces ar reciprical, and since the earth is more massive, the moon is subjected to larger tidal forces than the earth. Exept that even were there seas on the moon, they would not have significant tides. …because the the earth is almost stationary to a lunar observer. The tidal forces from the earth are credited with bringing the moons rotation into sync with it’s orbit. As well as the evidence of heavy vulcanism in the moons early history.

The vulcanism angle may relate to evolution on earth. Certainly vulcanism is possible, even likely without the influance of a massive satillite, but it is very likely that the moon’s influance greatly increases terrestrial vulcanism, plate movements, etc. Sulfer and other compounds which spew from volcanos is thought to have played a part in pre-life amino acid formation.

Also, there is overwhelming evidence that evolution took a huge turn when a massive metore struck the earth, causing massive extinctions, the rise of mammals, etc. It is likely that the moon provides some shielding from this type of catastrophy (though many think it was formed by just such an event). If that were true, it could give various life forms a longer time window to evolve before being “reset” by the next big smackaroo.

10

One significant effect the moon has had has been to slow the Earth’s rotation (and it continues to do so, albeit at a diminishing rate, until the Earth and Luna are in tidal lock). This certainly has had an impact on photosynthetic organisms and meteorological conditions, though its individual contribution to the evolution of life is highly complex and not easily quantified.

It used to be thought that a large moon “skimmed” atmosphere from the Earth, and the lack of a large, close moon would result in a greenhouse world like Venus, but that theory has fallen from favor decades ago.

Although the human menstraul cycle is roughly equivilent (on average) to the lunar cycle, this appears to be a coincidence, and is not the case for other mammals who have eustrus cycles that do not mach lunar rhythms. The Master speaks on this topic.

And of course, having a local moon with a high albedo has led to numerous romantic sonnets involving that phenomenon, without which it is sometimes doubtful that the female Homo sapiens sapiens could be compelled to cojoin with the male member of that benighted species and thus perpetuate the germ line. Think of it as a counter-influence to NASCAR and pee-splattered toliet seats. Og help us when a contingent of militant feminist genetic bioengineers figure out how produce children from two ova; men’s only saving grace then will be our ability to read maps and open pickle jars. :stuck_out_tongue: ::ducking for cover::

Stranger

11

I’m a little vague on my citations too, but I recall that at one time there was another popular conjecture around: that the Moon was necessary for thinning the Earth’s atmosphere enough to prevent the planet becoming like Venus. Larry Niven used this idea for the premise of at least one of his science-fiction short stories. Not that I’m citing Niven as an authoritative source here.

However, I believe that this conjecture has long ago fallen out of fashion among planetary astronomers. (On preview I see Stranger beat me to this.)

It’s now hypothesized that the Moon is probably the result of a massive collision that the Earth experienced, very early in its history, with a body approximately the size of Mars. Collisions with large meteors — and damn if that ain’t a large meteor — would have been very frequent in the solar system’s early period, although a huge collision like that would have been a singularly rare event. And so, the Moon could certainly be a fluke, astronomically speaking.

Whether the Moon, as a generator of ocean tides, was essential to life’s development on Earth is of course a different question. But in any case, it could be that the increase in mass that the Earth underwent, in this ancient collision, was essential to the development of life later on. So Earth anyway is probably a fluke — but that we already knew.

It’s only a coincidence in “recent” times — recent on geological time scales that is. In the solar system’s early history, the Moon was much closer to Earth, and would have appeared noticeably larger than the Sun when the two were close together in the sky. Eclipses of both kinds would have been more frequent, and solar eclipses would never have been annular. (Only total, or partial.)

I’ll admit though that it’s a startling coincidence that the time when the Moon and Sun’s angular diameters match each other happens to be about the same time that a species of hairy chimpanzee achieved sapience, built cities, and started making telescopes and space probes. You wouldn’t have predicted that to happen, four billion years ago.

12

Chronos gave us Why does the same side of the moon always face the earth?. After reading that, I finally felt that I understood tides. Please read it. It is a classic.

13

Wrong Way Street. And you could cite worse authorities than Niven: he likes his science pretty durn hard (even if he had the Earth rotating backwards in the first edition of Ringworld, and the Ringworld itself was unstable).

Ah well, we can probably invoke the anthropic principle again…

14

The second link in that column to a Cecil column is busted, currently it is at Why are there high tides twice a day when the earth rotates beneath the moon only once a day?

Cecil disagrees with Chronos. We discussed this in a previous thread

I would say that your “lie to children” is closer to the truth.

The Bad Astronomer’s explanation agrees, and agrees with Cecil’s.

15

Wow, I can’t believe I’m the first to mention this. But even if the Earth had no large moon, there would still be tides caused by the sun, albeit smaller. Whether or not the difference in size would change the probability of land-based life developing or not is left as an exercise for the reader.

I remember Asimov writing about this, I think he more or less concluded that possibly life is fairly common in the universe, but land-based life is very rare. Hard to work metals in the ocean.

16

Triple Triumph of the Moon, by Isaac Asimov:

17

Not really. Metals precipitate readily in the ocean; see manganese nodules. It is, however, hard to generate rapid oxidation required for high energy reactions, as we do with fire, which creates some limits on tool-making ability. One imagines that a sentient sea-borne life would have to build technology on electrochemistry rather than fire-based metallurgy.

Sealife has no problem developing tool-using capability, though. Witness the octopus.

Stranger

18

A book related to the OP:

What If the Moon Didn’t Exist?: Voyages to Earths That Might Have Been

I used to have a copy; pretty good read.

19

I think that what you mean is that an elliptical orbit is stable: That is to say, that if you have two point masses in the Universe, and they start off in an elliptical orbit, they’ll stay in that elliptical orbit forever. Unfortunately, our Universe is a bit more complicated than that, with considerably more than two objects, most of which aren’t points. As a result, there are many forces which can change orbits, and if an orbit is changed by some means, there’s no “self-correction” which would cause it to change back. As it happens, most of the factors which change orbits tend to cause them to become more circular: This is why the orbits of all of the planets and most moons and asteroids are so close to circular. In the case of the Moon, the primary circularizing effect is tidal forces, but friction with an atmosphere or the interplanetary medium, collisions with other orbiting bodies, and relativistic effects, where they’re relevant, all tend to cause orbits to become more circular.

On the question of the likelihood of life/intelligence/civilization, etc., we have very little data, having only one world known to have life, and only a handful more where we can even attempt to detect it (at least with current technology). We’re still not convinced that Mars never had life (though we’re pretty sure it doesn’t now), and we don’t even have a clue yet about Europa (the next-best prospect known, after Earth and Mars). Outside of our Solar System, we can’t even detect an Earthlike planet yet, much less any hypothetical life it might bear.

However, that one data point does tell us a few things. Most obviously, it tells us that life is at least possible. Perhaps more significantly, life on Earth arose very early, in the Earth’s history, showing up only a few hundred million years after the crust solidified. I believe it was Carl Sagan who argued that this rapid appearance of life on Earth suggests that life is very likely to arise, given the opportunity.

As for the question of communication with alien intelligences, the first message would tell us little more than the fact that we’re not alone (which itself would, I think, be a significant enough finding to justify SETI). But that would not be the extent of it. While the first message would probably just be a list of prime numbers or digits of pi or some other such proof of sentience, more messages would follow. Any civilization which has developed radio is bound to have learned a thing or two in the process, and they could share that information with us. Even if we assume that their technology is on average at the same level as ours, it won’t be the same as ours. Some things that they’ve discovered would have been overlooked by us, and vice-versa (of course, there’s no way of knowing just what those discoveries might be). Both civilizations could only benefit from exchanging notes in this manner.

Stranger on a Train, I, too, had heard the hypothesis that the Moon was partly responsible for the Earth’s thin atmosphere, but I hadn’t heard that it had passed out of vogue. What is the present dominant explanation for why our air is so thin?

20

42, of course!
Seriously, though, I seem to recall that one of Steven Baxter’s “Manifold” books included descriptions of alternate Earths with different sized moons and how they affected human evolution, if you’re interested.