Possible Explanations for Earth's Unique Characteristics

[Andre]

The issue was not so much the tides as the spin axis stabilisation

 

[Richard111]

True. Without a moon of sufficient size there would be no stabilisation.
Without water in the liquid phase no tides and maybe no life.
All seem unique to me but as mentioned above how do you confirm this planet is unique in the observable universe?

 

[D H]

No tides? No. There will still be solar tides. With regard to uniqueness, we do not know. At present, the only confirmation regarding the uniqueness (or lack thereof) of the Earth is a sample size of one: Our own solar system. Assessing this hypothesis with respect to a tiny chunk of our galaxy but outside our solar system might be possible in the near future. Assessing it with respect to the observable universe at large? Never.

 

[Richard111]

Ooops, yes. Solar tides. But would that have been sufficient to maintain spin stabilisation? Would the limited range of solar tides have encouraged life to adapt to less exposed land surfaces?

The geological time required for life, from first appearance in water, to adapt to dry(ish) land was far longer than the time to present.

Without the moon, life as we know it may not have been possible.

There is geological and paleontological evidence that the Earth rotated faster and that the Moon was closer to the Earth in the remote past.

http://en.wikipedia.org/wiki/Tidal_acceleration

 

[Ophiolite]

Plate tectonics. The stabilisation of atmospheric composition, the presence of terrestrial environments in addition to the marine, the maintenance of mean temperatures in the stability range of liquid water, all of these would not be possible without active plate tectonics. This in turn is contingent upon stochastic processes in the accretionary disc from which the Earth formed, in as much as this determined crustal thickness and established whether plate tectonics would be a long term affair as on Earth, a short term affair as on Mars, or a periodic catastrophic affair as on Venus.

 

[Andre]

Plate tectonics. ... or a periodic catastrophic affair as on Venus.

What evidence is there to substantiate that the apparent catastrophic affair on Venus was periodic, rather than unique, one time only?

 

[Ophiolite]

There are two principal options:
1. The resurfacing event that occurred around 600 million years ago and the stagnant lid period that preceded it, were themselves preceded by 'conventional' plate tectonics.
2. The resurfacing event etc, was the most recent in a series of such events.

You have to dispose of the internal heat. These are the two obvious mechanisms. I have a gut feel - unquantified - that continuous conventional plate tectonics should have maintained water content on the planet, so I lean to the possibility of periodic resurfacing. The evidence is consisten with either.

 

[D H]

Ooops, yes. Solar tides. But would that have been sufficient to maintain spin stabilisation? Would the limited range of solar tides have encouraged life to adapt to less exposed land surfaces?

AFAIK, the tides are not the mechanism by which the Moon aids in keeping the Earth's rotation stable. Tides are dissipative forces. The same gravity gradient forces that cause the tides also induce a conservative torque on the Earth as a whole. This torque, averaged out over the Moon's 18.6 year nodical period, results in the 26,000 year lunisolar precession.

Without the moon, life as we know it may not have been possible.

Emphasis mine. This is purely conjectural.

There is geological and paleontological evidence that the Earth rotated faster and that the Moon was closer to the Earth in the remote past.

I am not debating that the Moon slows the Earth's rotation rate. That is a fact. What is debatable is whether the Earth's day would be eight hours long if the Moon never existed. If indeed the Moon formed from a collision between the Earth and Theia, we do not know how much the collision itself changed the Earth's rotation rate.

 

[Andre]

There are two principal options:
1. The resurfacing event that occurred around 600 million years ago and the stagnant lid period that preceded it, were themselves preceded by 'conventional' plate tectonics.
2. The resurfacing event etc, was the most recent in a series of such events.

You have to dispose of the internal heat. These are the two obvious mechanisms. I have a gut feel - unquantified - that continuous conventional plate tectonics should have maintained water content on the planet, so I lean to the possibility of periodic resurfacing. The evidence is consisten with either.

but these are still suppositions following assumptions about heat and heat production in the core, which are also hypotheses. How many times did Venus lose its spinning energy for instance (due to the chaotic zone)? and how about possible relationships there?

 

[Ophiolite]

but these are still suppositions following assumptions about heat and heat production in the core, which are also hypotheses.

There are no assumptions here, only reasonable deductions leading to plausible hypotheses.
You will note in an earlier post I talk of two principal explanations. I do not rule out other possibilities, but simply find these two are the most probable based upon our current understanding.

Since I also think Venus suffered one or more catastrophic collisions akin to what formed the moon, or stripped mantle from Mercury, then issues of angular momentum cease to be insoluble problems.