# Most abundant elements on earth?

1. May 3, 2014

### Lapidus

All sources I have found on the web give the abundance of the elements on earth measured by weight. By that oxygen is number one or iron, depending on where you look.

But when counting just the number of atoms wouldn't that make hydrogen number one?

thanks

2. May 3, 2014

### SteamKing

Staff Emeritus
I think you need to be clear here. Are you talking about abundance for the entire earth or just the crust, or what? In the crust, hydrogen is relatively rare, whereas silicon is as common as sand at the shore.

3. May 3, 2014

### Lapidus

Thanks for replying. I meant the entire earth. Why would I ask for the crust, what is so special about it?

And is hydrogen mainly just in the water, but rare in the inner earth? Does oxygen in the air, in the water and in the crust outnumber the double number of hydrogen atoms in water?

4. May 5, 2014

### phyzguy

Why don't you try some calculations? For example, how many oxygen atoms are there in the Earth's mantle? How does this compare to the number of hydrogen atoms in the Earth's oceans?

5. May 5, 2014

### SteamKing

Staff Emeritus
In case you haven't noticed, it's where humans live and spend most of their time while alive. It's also quite handy for doing experiments, like finding out the relative abundance of the elements. You also have to look at published tables of elemental abundances on earth, because they usually contain disclaimers like 'for the earth's crust.'

We can analyze lava flows to determine the composition of the upper mantle, and we can theorize what the core is composed of and estimate its size based on gravitational measurements.

What phyzguy suggested. A good candidate for a 'back of the envelope' calculation.

6. May 5, 2014

### davenn

because its where most of the elements are found

D

7. May 5, 2014

### phyzguy

What do you mean by that? The Earth's crust is less than 1% of the Earth's volume.

8. May 5, 2014

### Staff: Mentor

I think he means that practically all of the elements we physically find are located in the crust since we can't get any from anywhere else in the Earth.

9. May 6, 2014

### davenn

so true at least someone understood
and also consider you will most likely find most of the lightest element are in the crust and lithosphere rather than in the mantle or deeper

Dave

edit .....

http://en.wikipedia.org/wiki/Abundance_of_elements_in_Earth's_crust

http://hyperphysics.phy-astr.gsu.edu/hbase/tables/elabund.html

http://www.periodictable.com/Properties/A/CrustAbundance.an.log.html

Last edited: May 6, 2014
10. May 8, 2014

### abitslow

You need to consider how aggressive your rhetorical question sounds about why you would ask such and such. Why would you ask about number of atoms? Same reason you'd ask about the crust, I suppose: because you are interested. Based on what we know, the Earth's core is mostly iron. But we haven't been down there to check. So, the Earth's composition is quite speculative. Obviously, if Fe and O are approximately equally abundant by weight, then by number, O wins hands down. Hydrogen would have to occur in high concentrations to be the most numerous...but then again I don't think we can rule it out with any certainty (as water and hydrates). As far as your comment about the Crust "only" being a fraction of the total, yeah we exist on what many have called scum floating on the mantle. But then again who says quantity is more important than quality?

11. May 8, 2014

### Ophiolite

Hydrogen in the core: practically none
Hydrogen in the mantle: minor role in a few hydrous minerals
Oxygen in mantle: abundant, since it - with silicon - forms SiO4 tetrahedra, the backbone of the silicates of which the mantle is largely composed.
The crust: irrelevant because of its low volume.

Oh, and as to why people may have thought you meant the crust, you asked about elements on the Earth, not in the Earth.

12. May 8, 2014

### Redbelly98

Staff Emeritus
Agreed. Note davenn's choice of words: where most elements are found is not the same as where most elements are located.

13. May 12, 2014

### my2cts

If you divide whatever abundance by weight numbers you have, crust core or atmosphere, by the atomic weights, you get the abundance by numbers. This will enable you to decide which is the most abundant element by number. ;-)