Why aren't heavier metals like uranium and mercury found in abundance in the core?

danielandpenn

I'm curious as to why there aren't heavier metals in the earth's core than iron and nickel. Why those two? Anyone have any insight?

tiny-tim

Hi danielandpenn ! Welcome to PF!

There are … see http://en.wikipedia.org/wiki/Core_(earth_science):

Almanzo

Nickel and iron are more abundant in the universe (or at any rate in the Solar system) than heavier substances, and might therefore dominate the core even if most of these other substances would have accumulated there.

On the other hand, some substances, like iodine, or mercury, might be mostly locked into molecules with less density than iron, or dissolved into subtances with less density than iron, like aluminium or water, and might therefore not be more abundant in the core than in the mantle or crust.

Andre

Welcome, Danie

What happens in the core is all pure hypothetical, since we have only some very indirect observations. The wiki ref of tiny-tim is certainly true qualitatively but there is no way of quantifying the concentration of heavy elements in the core as well as their contribution to the terrestrial generated heat. There are more hypotheses going around, none of which can be selected as being the right one.

The iron - nickle abundance is no doubt related to the total abundance of those elements in the solar system, whereas the heavy elements are much more rare.

Another element could be, the order in which compounds became fluid or not, during the -hypothetical- iron catastrophe

But in the end it's all a sophisticated guess.

baywax

Gee, I thought it was one big diamond at the centre... or is that Jupiter

Actually, I'd like to ask a question related to this one.... and that is why is gold associated with volcanic activity? Does it get separated out by extreme heat or is it of greater abundance in the liquid magma surfacing during a volcanic eruption?

Many thanks!

mgb_phys

Gold isn't very chemically active but is soluable at very high pressures. It is carried along cracks by steam/fluids from volcanoes and is deposited out as they cool. So are lots of other metals, there a bunch of elements like platinum and telurium that you find along with gold.

baywax

Ah, right! The chinese who built most of the CN and CPR railways across Canada would keep what they called "white gold" (platinum) in their old opium jars. It was considered useless at the time by the CDN and USA placer miners, but the "Coolies" kept it just the same.

Almanzo

If the core of Jupiter is made of diamond, that would mean that carbon is dominating Jupiter's core. One would have to conclude that elements heavier than carbon (such as iron and nickel) are relatively rare on Jupiter. In that case iron and nickel cannot be all that common in the Solar System, and one would have to wonder why they are common on Earth.

That is quite different from the case for hydrogen. Hydrogen is the most common element in the universe, but Earth cannot keep hold of it (except in compounds with heavier elements, such as oxygen), because it is light enough to escape from Earth's gravity well. Jupiter is more massive, and was therefore able to retain more hydrogen.

Carbon, however, would not escape from Earth, at least not over the present age of the Solar System. If a large part of Jupiter is made of carbon, that would be strange.

baywax

Very interesting. Do we know what the predominant metal/other is at Mar's core? Does the volcanic activity of Io, next to Jupiter, indicate a core content similar to earth's?

mgb_phys

We don't have direct seismic data for mars but it is thought to be similair to Earth. The difference is that Mars is smaller and so it's core cooled and solidifed and so has no (significant) magnetic field.

The volcanic activity of Io is due to the energy input from Jupiter, from tidal forces, it is too small to have a liquid core purely from internal heat sources. It does look like it has an iron core from magnetic field measurements made by the Galileo probe.

Gokul43201

To my knowledge, there is no real evidence of any significant amounts of carbon in Jupiter's core. The diamond core theory was made up by Arthur C. Clarke for one of his later Odyssey novels.

There is definitely more realistic speculation of metallic hydrogen in jupiter's core, but I don't think that's been verified either.

sketchtrack

Wouldn't it be too hot for diamonds in the core of a planet? Wouldn't they burn up, or would the pressure prevent that?

baywax

I'm sorry, I mentioned the diamond centre of Jupiter as a joke... sort of sarcastic kind of thing.

mgb_phys

You need oxygen for things to burn, also Carbon has a rather high boiling point (4000K)
Diamond isn't the most stable form of Carbon, diamonds (slowly) decay into graphite at room temperature - I don't know about at the pressure in the centre of a planet

baywax

So, how long till the engagement diamond turns into a pencil? Probably longer than the license takes to decompose, eh?.

Andre

Boiling point of carbon is even a bit higher, 5100K and the melting point (grafite) is 3773K. The temperature of the Earth core is estimated at about 4-5000 ^oC. But the tremendous pressure would probably prevent carbon to be fluid.

sketchtrack

Could one assume that if there is carbon in or near the core, it is probably in diamond form?