With Earth’s moon around to absorb asteroid impacts and control the tides, is it safe to say life on Earth depends on it? And therefore any extrasolar planet, you’d stand to reason, must also have a moon if it’s to support life as we know it?
It’s difficult to say, given that we only have a sample size of one. But my guess is that it isn’t necessary for unicellular prokaryotes. At the very least, roles could be reversed, such as with Europa (potentially playing the role of Earth as the place with life) and Jupiter (potentially playing the role of absorbing asteroid impacts and causing tides).
There’s really not much of a factual answer on this since we have no way of knowing unless we find life elsewhere.
A moon isn’t a necessity. Ocean tides aren’t all that valuable, and our moon hasn’t been all that much protection from asteroids and the like. Moons may be helpful in achieving an Earth-like atmosphere at a reasonable time in the life of a planet.
The Moon offers very little protection from asteroid impacts. Cite.
However the early Moon’s magnetosphere protected Earth’s atmosphere from being eroded by solar storms. Cite.
Personally, I think that although the Moon did have some benefits for life on Earth, I’d find it hard to believe that such a situation was NECESSARY for life. Certainly in very alien environments, like in the subsurface oceans of Jovian moons, or in the atmosphere of a gas giant, the effects that the Moon has on Earth would be completely irrelevant.
There’s a bunch of different issues here. There’s no definitive answer about the moon’s role in promoting life on earth, but there’s no question that it has important influences on present-day life due to the tides, helping to cycle nutrients and distribute marine organisms. The moon’s sudden disappearance would have significant ecological effects. The moon also has a very important effect in helping to stabilize the earth’s axial tilt, which promotes a more stable climate conducive to life.
I don’t think the moon plays much of a role in protecting us from asteroids as it’s not much of a shield.
Tides probably accelerate the evolution of land-based life. Mature aquatic life gets caught in tide pools, and some of that life will adapt to breath oxygen and walk on land. That transformation could happen without the moon, but the tides will cause lots of living creatures to get caught in areas with limited water, which forces them to adapt or die. Without the moon, many fewer creatures would venture out of the water and adapt to life on land.
I don’t think the moon does absorb asteroid impacts to any meaningful degree. Asteroids aren’t “sucked in” by the moon (or the Earth), they hit if the path of the Moon/Earth happen to cross the path of the asteroid. That means that the moon just happening to be in the exact right position to take a hit that would have otherwise hit the Earth several hours later would account for a very small percentage of potential asteroid strikes.
“You see the dent in this silver dollar? My great-grandfather was carrying this silver dollar in his shirt pocket during the war. It stopped a bullet that would otherwise have gone straight into his heart…shame about the other 29 bullets.”
There would still be tides if there were no Moon, because the Sun raises tides too. They’re only half as strong as lunar tides, though. However, in the early days of the Earth, the Moon was a lot closer so its tides were much more extreme, while solar tides would have been about the same as now. AFAIK, we can’t say that they were required for life or for some specific development such as life moving from the sea to the land.
Jupiter is much more important with keeping the solar system clear of potentialy dangerous objects than the Moon.
Even if the Moon were required for life on Earth, that would be because life on Earth evolved with the Moon’s effects in place.
We have no idea what changes there would be to life on Earth if we didn’t have a Moon, but there’s nothing to suggest that life would be impossible.
I would not go quite so far as to say “nothing to suggest …”.
The most common claim for the Moon’s benefit is spin axis stabilization.
The claim (which I’m not competent to independently evaluate) is that absent the Moon, the Earth’s spin axis would be prone to large wanderings of geological timespans which would devastate local ecosystems faster than they could develop anything much more advanced than, say, algae or bacteria.
So not an impediment to at least some lifeforms, but a significant impediment to anything very interesting, let alone anything very intelligent.
If your claim was just “some life” vs “absolutely no life”, then I’d lean much closer to agreeing with you that the Moon is (probably) immaterial for passing that low bar.
In the early days of life on earth, the moon was much closer to the earth and the day was only five hours. So there would have been huge tides every 2 1/2 hours. The size of the tides varies as the inverse cube of the distance. I have forgotten how close the moon was, but I think there could have been 100’ tides. I wonder how life even survived under such conditions.
To change the subject, I have a friend who conjectures that having a moon whose apparent size is more-or-less (literally, sometimes more, sometimes less) than that of the sun was necessary–or at least conducive–to the development of intelligent life on earth. His argument was that eclipse prediction led to early mathematics and physics.
I was going to mention spin axis stabilization, but that always seemed speculative to me (that life would require a stabilized spin axis). But maybe it’s a possibility, so I guess I should have said 'A small bit of evidence to suggest…" instead.
By the time life appeared on Earth, the Moon was much further away. 500 million years after impact, the Moon had receded to about 60,000 miles - about one third of the current distance. Tides would have been higher, but nothing like 100’.
That sounds unlikely. Early math was much more likely to have been tied to agriculture and trade. Did the greeks mention eclipse prediction in their development of math?
In addition to axis stabilization, the moon has kept the earth’s outer core liquid and spinning. Without that, the earth’s magnetic field would be weak or nonexistent. No guarantee that life could form or survive without its protection.
I also recall one article that said that if not for the moon we would have a dense atmosphere like Venus, not condusive to life. Theory was, over geological time, the moon plowing through the extremely tenuous edge of earth’s atmospere appreciably drew off the gases, causing them to accelerate to escape velocity. It sounds implausible, and Mars would be the counter-example.
I think we’re overall in agreement. I too find the spin axis thing a bit flaky.
I do agree that a watery planet orbiting a decent distance from its star and with a decent day length but that also axially precessed wildly, like through 90 degrees every 10 million years or so, would play havoc with the long slow evolutionary climb from prokaryotes to humans. Even though otherwise the planet as a whole might be hospitable to basic life.
What has always seemed flaky to me is the idea that the large Moon necessarily provides stability. Rather than being a big enough influence to occasionally send both bodies’ parameters careening off in a chaotic direction. Has always smelled a bit like a “just so” story to me. But that’s a rank layman talking.
As I recall astronomy discussions, that Neptune has a extreme tilt is considered an extreme anomaly. If a comparable sized moon were necessary to maintain axial sability, why are so many celestial bodies consistent in their axial tilt?
Also remember that there has been “snowball earth”. Supposedly the entire earth froze over somewhere in the past few billion years, yet life survived.
Part of the reason for speculation about the Moon’s role in evolution of life is that, from what we can tell, the Earth appears to be special in two and only two ways: We have an unusually large Moon, and we have life. Whenever you find a specimen that’s unusual in two ways, it’s natural to speculate that those two things might be related. And from there, folks try to figure out just how they’re related.