GeologyRocks

Someone call?

Tomography does not have this resolution but good old fashioned seismology does. Probably what is being used here is the reflection from the inner/outer core boundary (PKiKP) and comparison with the P-wave through the outer part of the inner core (PKIKP)

Tomography isn't the be all and end all. Like Hypocentre says reflected waves from the inner/outer core boundary could be used to image the boundary, although at those depths I am not sure how that resolution could be acheived.

There has been work done on the irregular D'' layer (just above the outer core IIRC), where diffracted waves from the irregularities, recorded at the surface, can be focused with high precision back to the place where they came from. This is similar to imaging processes used in exploration geophysics.

I always liken seismic tomography to trying to look at a member of the opposite sex through a frosted shower screen. You know that there is something quite interesting going on behind there - but you can't quite make out what it is!

Changed my reply as it made me sound like a bit of a know-it-all, sorry

It's never stopped me

probably sound stupid here, but i thought that the inner core was hotter than the outer core. so how could the inner core grow by:

Wouldn't the 'frozen sediments' actually have to heat up? and then let pressure solidify them? :?

Not sure on that one but surely pressure must play a part.

I really wouldn't be using wikipedia for any reliable geo-information. Especially not for school/university stuff!

What do they mean by 'frozen' sediments anyway?

I thought 'frozen' just referred to water and would therefore require temperatures of 0C (at 1Atmosphere). Whilst I know the pressure is immense at the inner/outer core boundary so is the temperature.

And just what 'sediments' can sink that far? Surely only the heavy elements can make it to the core - especially given convection cells in the mantle.

Might have to look at the wikipedia article to see the context.

I think the word frozen here means anything that was once liquid, and is now solid.

maybe the sediments are of eroded depleted-uranium

Isn't sediment a solid by definition? :?

but there's no sediment in the mantle or cores. that implies erosion from a solidified rock, namely at the surface.

so that just sounds wrong.

If there's anything going on, maybe some liquid is crystallizing and being moved around because of its denser quality. Or elemental differentiation is still ongoing, so bits of iron and nickle and whatever else are slowly making their way down to the core and joining in, making it larger as the mantle shrinks due to the loss.

So it was probably deduced from other more accurate seismic techniques than tomography... thats cleared that up- thanks

Nice analogy!

Don't worry, this is just from a discussion someone brought up on another website. I wouldn't touch wikipedia with a barge-pole for uni work.

Personally I really rate Wikipedia as a free on-line reference service. You just have to critically analyse all that you read (which no doubt everyone does for everything anyway, even peer-reviewed papers). Back in the day when I was a student we searched random homepages for information never having a clue how reliable it was.

To pick on one sentance in an entire article to dismiss the site is a flawed argument. Besides the very essence of Wikipedia is that you can go in and change the article to correct and improve it.

Still, I'd never rely on it as a single source of evidence for uni/work/school. But then again I'd never rely on any single source of evidence - that's the way Creationist thinking works!

PS: No, I don't own shares in wikipedia

I am doing various essays for my A-level geology course, and quite often when you search a technical name, guess whats at the top of the list? Wikipedia.
It is useful as there are only a few other sites, GR included, that have good enough technical facts for a-level and above students to use.
But i do agree that if you take a fact from wiki, try to look it up, to make sure it is actually a fact!
Although personally i prefer:
http://uncyclopedia.org/wiki/Main_Page

When I gave my talk recently, I used google as an example of what people find when looking stuff up. My aim was to show how high creationist sites appear, but wikipedia was second on a lot of searches.

There are two problems with wikipedia:
1 - no check on reliability (GR addresses this by editorial means and wikipedia are doing likewise for "controversial" topics)
2 - what you look up today may be different when you check tomorrow (although you can look at the history) because anyone can edit the page.

Having said that, wikipedia is an amazing idea and resource. I've borrowed a lot of ideas from them for GR3

OK, so what actually fuels the inner core, anyway? Can anyone comment here? I've heard several different arguments and I would like feedback on them.

The first line of reasoning goes: (a) If it were only gravitational compression the earth would be solidified by now (a la Mars), (b) the heavy, radioactive elements are more dense than iron, therefore (c) heavy metals sink near the center, form nuclear furnaces and a significant amount of heat comes from radioactive decay. (Of course, if it gets too hot, convection can break up the pockets of nuclear material, too.) I think this argument sounds the most plausible.

A second line of reasoning follows: (a) most uranium compounds (with the exception of uranium sulfide) are lighter than iron, (b) therefore they float around in the mantle and don't sink to the core, therefore (c) radioactive decay does not play a major role in keeping the core hot and it's all gravitational contraction.

A third line of reasoning is: (a) solar input nearly matches earth thermal output, so (b) therefore it's all solar. (Gravitational contraction supplied most of the heat until the earth cooled to the point where it was balanced with solar input, and now it's in a state of equilibrium until solar output changes significantly.)

I don't have numbers on any of this so I can't really tell which is right, if any, and which are wrong. The second argument seems wrong to me, though it is also very popular, because I imagine chemistry breaks down (all uranium would be elemental) at temperatures of 7,500 - 10,000 degrees (F) such as are found at the core. Is that not the case, or am I missing something (e.g., the effects of pressure)?