fusion in the earth's core?

[bwanaaa]

clearly there are naturally radioactive elements in the earth and there have been found naturally occurring fission reactions.

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

The existence of such a violent reaction occurring naturally makes wonder about the possibility of fusion as well. Of course, How it might have gotten started is anybody's guess (but isnt iron the end product of fusion in the sun? and isnt iron so abundant in the earth's core?) But getting back to the idea, is there anything theoretical or experimental to exclude the possibility of a small fusion reaction occurring in the earth's core? Would seismic data be able to exclude the presence of plasma at the core?

 

[CitanUzuki]

I thought iron was too heavy of an element to be produced by a star as small as our sun?

 

[William Gaatjes]

I thought iron was too heavy of an element to be produced by a star as small as our sun?

You are probably right. The iron comes from the previous star generation.
The sun is at least a second generation star and it is speculated that the sun maybe be even an third generation star. Thus our star (and entire solar system) is the "child" of a former much larger and more powerful star and maybe even the "grandchild". Powerful in the sense to have enough mass
to do nuclear reactions to create heavier elements.

 

[f4phantom2500]

it seems quite unlikely for fusion to occur naturally within the realm of earth; it's such an intense process and the heavier the element proposed for fusion would require that much more pressure, temp, etc, that i wouldn't look any further than hydrogen fusion...even so the possibility of it happening on or in the planet naturally seems extremely unlikely. i know jupiter has oceans of hydrogen, the pressure is high enough such that hydrogen exists in liquid form, but i don't believe that, as far as we can tell, there is fusion going on even on jupiter. if it's not going on on jupiter, it's not going on on earth. but who knows for sure?


if you're suggesting that the iron in the earth's core (the core is solid iron, surrounded by a liquid iron mantle) is possibly the result of fusion reactions, then you're mistaken; the iron in the earth's core is of the stellar remnants of the sun's predecessor. it's existed as such since even before the moon existed, which means that any potential fusion reactions leading to an iron core would had to have concluded a long long time ago...but in any case the earth is not nearly suitable for fusion reactions resulting in iron.

slightly off-topic but you'll find this interesting:

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

 

[Lemon law]

The fact is, as a natural process, hydrogen will fuse with hydrogen, produce helium, and in so doing will release a small amount of energy in the process.

What this thread somewhat ignores, is the speed at which this natural process occurs. To have any sort of reaction rate requires three things, heat, pressure, and an abundant proportion of hydrogen. And given a star of enough mass, the hydrogen fusion process occurs spontaneously.

Now ask the same questions about the interior of the planet earth, where we have some heat, some pressure, and an almost total lack of hydrogen at the core of the earth, and the thread answer becomes obvious. And the chance that one highly energetic proton in a plasma state will collide with an another to form deuterium, a intermediate needed daughter process in hydrogen fusion, proceeds at a rate little faster than more concentrated hydrogen gas at room temperature. I assume we might be able to measure the increased reaction rate at the center of the earth, but its probably too small to notice.

Hot as the earth's core is, its still way too little heat, way too little pressure, to come even close to the interior of a star.

 

[Mr. Pedantic]

The Sun will not produce iron via fusion in any significant quantity for another 4 billion years or so. The process preferentially starts with lower AW species first, since they are easier to propel together. So Hydrogen for now and for another few billion years, then helium, lithium, beryllium, boron, etc.

The existence of such a violent reaction occurring naturally makes wonder about the possibility of fusion as well. Of course, How it might have gotten started is anybody's guess (but isnt iron the end product of fusion in the sun? and isnt iron so abundant in the earth's core?) But getting back to the idea, is there anything theoretical or experimental to exclude the possibility of a small fusion reaction occurring in the earth's core? Would seismic data be able to exclude the presence of plasma at the core?

Lack of heat, lack of pressure, lack of hydrogen. Just an indication, a body made primarily of hydrogen (like the Sun, or our gas giants) would have to be about 10 jupiter masses before spontaneous hydrogen fusion would start occurring. Jupiter is about 320 times more massive than the Earth.

That pretty much rules out fusion, you don't really even need to measure anything. Because of the boltzmann distribution it's possible there may be a few atoms of hydrogen fusing together once in a while (maybe), but certainly not at a great enough rate to sustain the reaction.

 

[Lemon law]

The other thing to point out is that an our own suns size star will never progress much beyond an ability to fuse hydrogen into helium, even in its death phase.

It takes a far more massive star to fuse elements as heavy as Carbon, and a far far more massive star than that to fuse elements up to Iron. Moreover, no first generation star, no matter how massive, can fuse elements up to iron in its death super Nova stage.

 

[Biftheunderstudy]

Moreover, no first generation star, no matter how massive, can fuse elements up to iron in its death super Nova stage.

Care must be taken with statements like this. What do you mean by first gen star? POPIII?
In either case it is irrelevant, Pop I and II can definitely produce elements all the way up to iron depending on their mass and the bigger ones which go supernova produce the heavier elements through rapid neutron capture when they explode.

As for Pop III stars (1st generation/1st stars), while there are many things about them which are unknown, their ability to produce metals is not disputed (as far as I could find anyhow). No reason for them not to form a degenerate iron core though.