All planets precess and change their axial tilt over time. Earty definitely gets some axial stabilization from the moon, but not necessarily all that much.
So even if the Earth could tilt 90%, it would take billions of years. Animal life operates on much faster time scales, and would easily adapt.
I think the ‘moon is nexessary for life!’ notion was just speculation by people pushing the ‘rare earth’ solution for the Fermi paradox. There’s no actual evidence that an axial precession of say, 1 degree every 30 million years would have any effect at all on the development of life.
I think that’s due to conservation of angular momentum. Unless something impacts a planet to change it’s momentum, all the stuff in the solar system should have very similar spin and tilt, since they all formed from the same disc of stuff.
Regardless of whether this is true, isn’t it the case that moons are fairly common amongst the planets? Sure, not every planet has one, but as far as we can tell, it’s not hard to find an extrasolar planet with a moon, right?
That would imply that all planets should have an axial inclination of 0 degrees. It doesn’t explain why any of them are tilted away from zero, much less why four of them are tilted at nearly the same amount.
Yes, but spinning objects precess around the axis of rotation. They wobble. The claim is that without the Moon the Earth would precess much more, destabilizing the climate. The counter claim is that there is no evidence of that looking at other planets, and that the math suggests the precession would take billions of years.
Besides, the Earth completely resurfaces itself on much shorter time scales. I’m not sure a slow axis rotation over billions of years would even be noticed by life.
There are moons, and then there are moons. The vast majority of moons are dinky little nothings of rock or ice, that couldn’t possibly have any influence on the goings-on on their planet. Phobos and Deimos mean nothing to Mars. The vast majority of the dozens of moons of the gas giants mean nothing. Moons the like of Io, Europa, Ganymede, Callisto, Titan, or Triton could mean something, but still don’t, because the planets they orbit are so large that they’re still negligible. Charon does mean something to Pluto, but that’s only because Pluto itself is also a dinky little nothing of ice.
And then there’s our own Luna. Despite orbiting a mere rockball, it’s up there in the same class as the largest moons of the gasballs (more massive than Europa or Triton). Luna does definitely have significant effects on Earth. And we can’t know for sure without the capability to detect extrasolar moons, but we have reason to believe that that’s pretty rare.
I think it was in a Jared Diamond book he mentioned that the Northern Hemisphere is generally more fertile by getting a lot more volcanic residue, which enhances soil richness for plants. Whether plate tectonics have an effect long term on what minerals are available for life, and their renewal rate, is an interesting topic.
Right. We don’t know they exist, but it seems likely. In our system, only two planets don’t have moons and in both cases we know a specific reason for that (Mercury – too close to the sun for a moon to have a stable orbit, Venus – retrograde rotation).
I’d always heard that too, but from what I’ve read recently it’s a bit more complicated than that. The orbits of most long-period comets is such that Jupiter’s gravity pushes most of them away from the inner solar system.
On the other hand, Jupiter is the reason that there’s an asteroid field and not a planet beyond Mars’ orbit. And sometimes Jupiter nudges asteroids towards the inner solar system.
I think there’s a reason a moon might promote detectable, intellegent extraterrestrial life.
Without our moon’s phases, we would have been slower to make sense of the heavens. On the other hand, just imagine if there were a planet or two whose phases we could have seen with the naked eye (and Venus comes pretty darn close to that, in fact I think I’ve read there are a few people with eyes good enough to barely make it out). I bet we would have recognized what planets actually are much sooner, and likewise would have been interested in exploring them much sooner. All of which also means we would have made more of a visible commotion to be spotted from afar.
No, but Stonehenge, which appears to be involved in eclipse prediction predates Greek civilization by a millenium. And early Hindu math involved trigonometry which is hardly needed for agriculture.
“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’.”
First, 60,000 is closer to a fourth of the current distance, which varies from 220,000 to 240,000 miles. Second, the cube of 3 is 27, so any place that has a 4’ tide today would have had 108’ tide then. I once stayed at a hotel along the Oregon coast that had a high tide mark well over my head, at least 12’ from where I was on a dry beach (although it started filling as I was there) and once stayed at a hotel along the Bay of Fundy where you could literally see the tide rise.
And the Antikytheria Mechanism, to the extent that we can understand it, appears to have been an eclipse calculator.
True if the effect of terrain on the tides is linear, but I’m not sure that’s the case. If the Earth were all ocean, the tides would only be a few inches: Any place where it’s more, it’s due to various effects of the terrain.