The origins of Earth

[DevilSolution]

I'm curious as to the nature of the birth of our planet, primarily because were sitting on alot of molten hot iron, and i cant imagine how we would have a molten iron core unless we were a star or a star created an almost perfectly spherical drop of iron, or if 2 stars collided and we managed to grab aload of iron from the process. I know iron is the one of the most common element in the universe but i thought that was mainly due to nuclear fusion from all the stars, most of which dont make many elements bigger than iron. I'd imagine if we were to have been made though gravity and bits of iron they would be solid due to how cold the universe is. Is it common for planets to have molten iron cores?

 

Also im aware that the higher density elements are only made from supernova, like all the radioactive elements, which leads me onto my next question, how do we have such rare elements? i mean from gold upwards these elements must be pretty rare yet we seem to have atleast an equal quantity in ratio terms to the amount that exists within the universe. Which is bizarre, to have an almost even spread of elements on a singe planet as there are elements in the universe is pretty unique.

 

How would we acquire some of the radio active elements? Given earths atmosphere burns out most of whatever enters with the rare occasional extinction or such but even then the probability must be minuscule, even before we had life and an atmosphere its pretty random to have such exact quantities of rare elements. I'm presuming mars doesnt have such vast quantities of radioactive elements or gold etc (though i am only guessing)

 

Also completely random and impractical BUT given we have 2 magnetic poles and the fact we spin on our axis, couldnt we use this conduct electricity, for example if the moon was sprung with totally in copper wire linked to us by nanotubes wouldnt we have infinite electricity?

 

Regards.

[Strange]

Also im aware that the higher density elements are only made from supernova, like all the radioactive elements, which leads me onto my next question, how do we have such rare elements? i mean from gold upwards these elements must be pretty rare yet we seem to have atleast an equal quantity in ratio terms to the amount that exists within the universe. Which is bizarre, to have an almost even spread of elements on a singe planet as there are elements in the universe is pretty unique.

 

I'm not sure why you think that is odd. I would assume, as an approximation, that the elements produced by past supernovae are pretty well mixed and distributed. So when a cloud of gas and dust starts to collapse to form a solar system then the quantities of most elements would be roughly the same everywhere.

 

 

Also completely random and impractical BUT given we have 2 magnetic poles and the fact we spin on our axis, couldnt we use this conduct electricity, for example if the moon was sprung with totally in copper wire linked to us by nanotubes wouldnt we have infinite electricity?

 

The Earth's magnetic field is incredibly weak. It can just about turn a needle suspended on a low friction bearing (I'm thinking of a compass). You need a pretty big magnet close to a coil to generate a measurable current (and a massive generator to produce useful amounts).

 

Also, the moon doesn't rotate (relative to Earth) so the coils would generate any current. And it wouldn't be practical to get the current back to Earth.

 

Apart from that ...

[Ophiolite]

Here is a simple, arguably simplistic, summary of the planetary formation process:

 

Giant molecular clouds, many light years across, are composed of hydrogen, helium and the full range of other elements previously produced and expelled into space by supernovae. As a consequence of gravitational instability, or pressure waves caused by recent, nearby supernovae, one or more portions of the cloud begins to collapse.

 

This leads to a central mass, the proto-sun, surrounded by a disc of gas and dust. (The disc form is a consequence of various interacting magneto-hydrodynamic properties of the collapsing cloud.) At this stage the proto-sun is radiating strongly, from the conversion of the kinetic energy of the collapse to heat, creating a temperature gradient within the disc. This determines what elements will condense out of the disc.

 

Condensation does occur, with "rocky materials" dominating in the inner solar system. The initial solids are tiny dust particles that through collision, then gravitational attraction, grow in size, leading to objects the size of asteroids and then lunar, or Mars sized objects. Scores of Mars sized objects existed at this stage. Some fell into the sun, some were ejected from the system and the rest, through further collisions formed the Terrestrial planets.

 

Once the objects attained sufficient size the heat generated by the impact of their formation, coupled with the radioactive decay of short lived isotopes with which the cloud had been enriched by "recent" supernovae, led to melting and the segregation of elements into siderophile (iron loving) and lithophile (rock loving) components. The iron and associated elements, being denser, moved to the centre of the planet, leaving a molten rock mantle that soon solidified.

 

I believe that answers all your questions, but to clarify a couple of points.

1.We have a similar mix of universal chemical elements, excluding hydrogen and helium because we formed from a well mixed GMC that had that "standard" composition.

2. Because, for example, Mars formed in the same way it has similar, but not identical composition. The differences are useful in determining the differences in history of the two planets.

[DevilSolution]

I see, very nice description. So do any of the other planets in our solar system have molten cores?

 

 

I'm not sure why you think that is odd. I would assume, as an approximation, that the elements produced by past supernovae are pretty well mixed and distributed. So when a cloud of gas and dust starts to collapse to form a solar system then the quantities of most elements would be roughly the same everywhere.

 

 

The Earth's magnetic field is incredibly weak. It can just about turn a needle suspended on a low friction bearing (I'm thinking of a compass). You need a pretty big magnet close to a coil to generate a measurable current (and a massive generator to produce useful amounts).

 

Also, the moon doesn't rotate (relative to Earth) so the coils would generate any current. And it wouldn't be practical to get the current back to Earth.

 

Apart from that ...

 

I'll read into it, see if our wide selection of elements is rare or normal.

[Ophiolite]

Mercury: Partially molten core, generating a magnetic field. Overall core size much larger, relatively, than the Earth, probably as a result of major mantle loss following a late stage collision during planetary formation.

 

Venus: Probably molten throughout, because of high proportion of impurities and high surface temperature.

 

Mars: Once thought to have solidified because of the small size of the planet, but now believed to be molten throughout. The probable high percentage of impurities has lowered the melting point.

 

The cores of gas and ice giants are of uncertain composition and phase.

 

I'll read into it, see if our wide selection of elements is rare or normal.

Definitely read into it, but I'll tell you in advance you will find it to be normal. What would be strange is if the gross ratios of the elements were to differ significantly from those found in the parent GMC.

Edited December 13, 2015 by Ophiolite

[studiot]

One further comment to add to Ophiolite's ecstacy.

 

The so called packing fraction curve determines that energy will be released by fusion for elements up to iron in the periodic table, and that causing fission of these elements requires an input of energy.

 

This is the normal process within stars. The building up of lighter elements to heavier ones as far as iron.

 

Conversely beyond iron in the table the positions are reversed.

Fission now releases energy and fusion requires energy input.

 

So to build up the elements heavier than iron (a great deal of) energy input is required.

This is achieved in supernovae, not ordinary stars.

 

When the supernova explodes its material over a region of space, the material then contains the heavier radioactive elements which seed the resulting stellar and planetary systems.

Edited December 13, 2015 by studiot

[Ophiolite]

When the supernova explodes its material over a region of space, the material then contains the heavier radioactive elements which seed the resulting stellar and planetary systems.

This could be misread. A more accurate, thought clumsier, statement would read ..... the material then contains pre-existing lighter elements and elements heavier than iron, generated in the supernova. Freshly created radioactive elements both heavier and lighter than iron are included.

[studiot]

Yup it takes a supernova to make the heavy elements.

 

Cain't be did in ordnary stars.

Edited December 13, 2015 by studiot

[imatfaal]

!

Moderator Note

 

new thread regarding Martian Vulcanism here - http://www.scienceforums.net/topic/92696-martian-plate-tectonics-or-not/

 

[pavelcherepan]

What about most other elements? Say, a red giant will produce a lot of elements up to iron but most of that will be in the core which will form the white dwarf. How enriched would the outer layers, that it will inevitably shed, be? (Obviously, apart from helium enrichment).