Life on Earth, and the Moon?! Does our long-lived geodynamo result from a major impact, or unique geological features?

[dfjchem721]

The convection of a conducting liquid alloy of iron and nickel inside the Earth results in the formation of its magnetic field. This field protects our atmosphere from the harsh solar radiation which would otherwise strip the atmosphere and water from the surface, leaving a barren planet like the rest of our rocky cousins.

Some have speculated that the impact of a planetesimal contributed additional iron-nickel alloy to enhance the field and its duration, and also formed the moon from the resulting ejecta. This would require major differentiation of the much smaller impactor, which some find doubtful at such an early stage of its formation.

Others believe this longevity relates to geological features which result in superior heat trapping within the mantle, dramatically slowing the core's cooling. (Mercury, despite its small size, has a magnetic field strength of about 1% that of Earth, and is believed to result from a molten core.) Whatever the case, we would not be here except for something unique about Earth that has maintained its liquid core for billions of years, and counting. Is the Moon part of the answer to our existence, or is it something else entirely?!

 

[Wolfshadw]

Personally, I believe the moon's tidal forces help to slow/stop the cooling of the Earth's core, but I have no science to back that up.

-Wolf sends

 

[dfjchem721]

Personally, I believe the moon's tidal forces help to slow/stop the cooling of the Earth's core, but I have no science to back that up.

You are not completely alone in considering this mechanism. Curiously it never crossed my path doing the research before posting this thread, so one might consider it an outlier concept (but just my cup of tea!).

So there clearly is some support for tidal forces, and it certainly seems possible. A quote from a 2016 abstract is below, followed by a link to the full article (and another to the original) :

"To maintain this magnetic field until the present day, the classical model required the Earth's core to have cooled by around 3 000 °C over the past 4.3 billion years. Now, astronomers suggest that, on the contrary, its temperature has fallen by only 300 °C. The action of the Moon, overlooked until now, is thought to have compensated for this difference and kept the geodynamo active."

The Moon may play a major role in maintaining Earth's magnetic field

The Earth's magnetic field permanently protects us from the charged particles and radiation that originate in the Sun. This shield is produced by the geodynamo, the rapid motion of huge quantities of liquid iron alloy in the Earth's outer core. To maintain this magnetic field until the present...

www.sciencedaily.com

For a link to the original article used in the above report see (abstract only) :

The deep Earth may not be cooling down

The Earth is a thermal engine generating the fundamental processes of geomagnetic field, plate tectonics and volcanism. Large amounts of heat are perm…

www.sciencedirect.com

 

[rod]

FYI, according to radiometric dating methods, the oldest rocks on Earth showing evidence of a magnetic field is 3.5 billion years old. MS BING [Aside from those contested Australian zircons, the oldest-known evidence of Earth’s magnetic field—rocks in South Africa—dates to around 3.5 billion years ago.], also https://www.scientificamerican.com/...rths-magnetic-field-is-older-than-we-thought/, "Analysis finds that the planet’s protective shield was in place by at least 3.7 billion years ago, as early life arose"

However, note that Earth developed in the spinning, protoplanetary disk and the oldest dust grains are said to be 4.568E+9 years old, The age of the Solar System redefined by the oldest Pb-Pb age of a meteoritic inclusion, https://ui.adsabs.harvard.edu/abs/2010NatGe...3..637B/abstract

Starting with the dust grains at 4.568E+9 years old and rocks dated 3.7E+9 years old said to show a magnetic field, this leaves 868E+6 years time delta. How did the Earth develop a livable magnetic field that we use today like for a compass?

 

[David777]

Sounds like mass density/spatial cubic area interphasing from continuation of inflation/deflation, expansion/contraction, gravity/velocity, speed, momentum on a differential continuum above absolute zero degrees. And probably for velocity indicative temperatures below zero not readily perceived from our relative dimensional position.

 

[David777]

Time as related to the Earth spin seems fairly inconsequential relative to the Universe. Much like math as an effort to segregate reality into manipulative differentials. Maybe just existence with a not so well understood technological low to no mass "fiber optic" tubular pressure sensitive energy conduit media, quite pliable yet resilient and minimal if any mass gravitational dimenuation in relative localized low mass interphasing. Existence with a template overlay necessary to our focused (differential segregation) graphic imaging. Most of our discovery accurate. Just not the whole elephant.

 

[rod]

FYI. The question I raise in #4 is similar to this report, 'Moon and distant quasars facilitate first measurement of magnetic field in Earth’s core', https://astronomy.com/news/2010/12/...-measurement-of-magnetic-field-in-earths-core

"The magnetic field strength in the core is 50 times stronger than that at Earth’s surface." "The cooling Earth originally captured its magnetic field from the planetary disk in which the solar system formed. That field would have disappeared within 10,000 years if not for the planet's internal dynamo, which regenerates the field thanks to heat produced inside the planet. The heat makes the liquid outer core boil, or "convect," and as the conducting metals rise and then sink through the existing magnetic field, they create electrical currents that maintain the magnetic field. This roiling dynamo produces a slowly shifting magnetic field at the surface. "You get changes in the surface magnetic field that look a lot like gyres and flows in the oceans and the atmosphere, but these are being driven by fluid flow in the outer core," Buffett said. Buffett is a theoretician who uses observations to improve computer models of Earth's internal dynamo. Now at work on a second-generation model, he admits that a lack of information about conditions in the Earth's interior has been a big hindrance to making accurate models. He realized, however, that the tug of the Moon on the tilt of Earth's spin axis could provide information about the magnetic field inside. This tug would make the inner core precess — that is, make the spin axis slowly rotate in the opposite direction — which would produce magnetic changes in the outer core that damp the precession. Radio observations of distant quasars — extremely bright, active galaxies — provide precise measurements of the changes in Earth's rotation axis needed to calculate this damping. "The Moon is continually forcing the rotation axis of the core to precess, and we're looking at the response of the fluid outer core to the precession of the inner core," he said."

It seems more studies are taking place to answer detailed question about how the Earth got its magnetic field, how long the field will last (it is decaying too), etc.

 

[Catastrophe]

"This would require major differentiation of the much smaller impactor, which some find doubtful at such an early stage of its formation."

If some body the size of Mars were not assumed to be differentiated at that early date, then presumably its heavy metals (in the chemical sense) would be readily intermixed on the proposed collision. How would this affect your proposal (either way)?

Cat

 

[dfjchem721]

There is some debate about the actual size and even number of major impactors that might have given rise to the moon. So your point is well taken regarding the differentiation aspect. It does appear that many people who have studied the longevity of our core buy into the "added alloy school".

Differentiation* as best modeled for planet-sized objects like the Earth and Mars is believed to occur during a very early stage of their formation. This happens when the internal heat from formation, radionuclide decay, and gravitational effects becomes so intense that much of the planet melts into a relatively uniform mixture. At this stage, differentiation can occur at a relatively rapid rate, with the heaviest elements sinking and the silicates etc. rising. At some point, the heat output decreases to where the surface can "crystallize", forming a hard shell, with differentiation likely continuing for some millions of years after it skins over.

Differentiation based on smaller sized objects is not so easily obtained due to heat loss and time of the body's "survival" before impact with another, larger body. Smaller bodies are likely to form iron cores, but on a longer time frame, or so the argument against "added alloy" asserts. Of course these are all based on models (the last thing he wanted to read, probably....).


* https://en.wikipedia.org/wiki/Planetary_differentiation

 

[Catastrophe]

An excellent summary!