Not too long ago, I made a video about Rare Earth elements.
Which turns out, for the most part, aren't that rare.
But this made me curious: if Rare Earth elements aren't actually all that rare, what elements are?
What's the rarest element on Earth?
Just a quick disclaimer: I'm going to be exclusively talking about the naturally occurring elements
in the Earth's crust, and not the mantle or the core.
I'm doing this, because anything below the crust is completely inaccessible to us, both in terms of mining and research.
The deepest hole we've ever dug, was the Kola Superdeep Borehole, at over 12 thousand meters.
While this is tremendously deep, Earth's crust can reach up to 40,000 meters deep.
Which means, the Kola Superdeep Borehole likely wasn't even halfway down before they had to stop,
due to heat from the Earth's mantle, causing too much damage to the mining machines.
Because of this, we don't actually have any precise measurements of what's beyond the crust.
Even lava, which comes from the mantle, mostly consists of material from the crust, that just melted from contact with the mantle.
Therefore, in reality - lava offers little insight into what's beyond the crust.
Our best estimates say, that core is 89% iron, 5.8% nickel, and 4.5% sulfur.
Which accounts for 99.3% of the material in the Earth.
But that remaining 0.7% is typical labeled as "trace elements", which bascially means "we don't really know".
Since it's those trace elements, that we're interested in - for this video,
we'll have to only look at the part of the Earth, that we can thoroughly study: the crust.
First, the most abundant element found in the Earth's crust is oxygen.
While most might think about the atmosphere and what we breathe, when hearing about oxygen,
it's more commonly found in the form of rocky oxides in the crust.
And in fact, all of the most common rock types in the Earth's crust are oxides.
Silicon dioxide is the most common, and the main compound in things like sand and quartz.
Other incredibly common oxides include: magnesium oxide, iron oxide, aluminium oxide, and calcium oxide.
Chances are, if you see a rock on Earth, it contains a lot of oxygen.
Just not in the form of gas, but in oxides.
In total, oxygen occurs in the Earth's crust at 465,000 parts per million.
Which translates into 46.5% of the Earth's crust. Yes, nearly half of the Earth's crust is oxygen alone.
Together, the 10 most common elements account for 99.3% of everything found in the Earth's crust.
Just like how the 3 most common elements do in the core.
The 10th most abundant element here is hydrogen, which at first I found surprising.
I mean, with only 1,400 parts per million, titanium is 4 times more abundant on Earth than hydrogen.
With an atomic number of 1, hydrogen is the most simple element in existence.
And there was a point right after the Big Bang, where there was nothing in the universe except for hydrogen.
To this day, hydrogen remains the most common element in the universe, making up 74% of all matter.
So you would think it would be fairly common here on Earth too, and well, technically it is.
But you know, not as abundant as everywhere else in the universe.
This wasn't always the case, though.
When Earth was newly formed, hydrogen made up roughly 40% of our atmosphere.
But because hydrogen is so light, most of it floated up to the very top layer of Earth's atmosphere.
Where the atmosphere sort of just fades into empty space.
Over time, the hydrogen just literally drifted away into outer space.
This process continues to this day, and even now, the Earth loses an estimated
95,000 tons of hydrogen each year, just from it leaking into space.
Okay, I've been talking about hydrogen for too long.
Carbon is the 17th most abundant element.
Which is interesting, because carbon is the basic element, essential for all life on Earth.
And is the second most abundant element in the human body, right after oxygen.
Today, carbon exists at 200 parts per million in our crust.
Below carbon, in the spot of the 25th most common element on Earth,
we have cerium, the first rare Earth element we'll see.
It occurs at 66.5 parts per million, again proving, that not all Rare Earth elements are actually that rare.
And we have some more Rare Earth elements just below this, too.
Like neodymium at 41.5 parts per million, lanthanum at 39 parts per million,
yttrium at 33 parts per million, and scandium at 22 parts per million.
Right below all of these Rare Earth elements we have nitrogen.
Which means the element, that makes up 78% of the air we breathe,
is more rare than some Rare Earth elements, at only 19 parts per million.
In total, 94 elements occur naturally on Earth.
That means the 47th most abundant element is halfway.
Which just so happens to be hafnium, which exists at 3 parts per million.
I don't know, I don't have anything else to say about it. I just thought that was a nice coincidence.
Right below hafnium we have uranium, occurring at only 2.7 parts per million in the crust.
But below uranium we have tin, at only 2.3 parts per million.
That means tinfoil (not aluminium foil, but real tinfoil),
is made of something more rare, than the fuel in most nuclear reactors.
Found at 1.2 parts per million, terbium is another Rare Earth element, and the 59th most common.
Or well, at this point, I should say the 35th rarest element on Earth.
This is also the last element, that occurs at over 1 part per million in our crust.
That means the next 34 elements after terbium,
even if you surveyed a million random atoms in the Earth's crust, you might not find one.
A bit more rare than that, and we have silver, the 26th rarest element on Earth, at 0.075 parts per million.
Which feels impressive, until we go a bit further down and find helium.
Which I guess, is technically the 22nd rarest element on Earth, occurring at only 0.008 parts per million.
In the rest of the universe, helium is the second most abundant element, only after hydrogen.
And it makes up 24% of all the mass in the universe.
In space, helium is created by the process of nuclear fusion in the center of stars.
Which kinda means stars are just large helium factories.
This also means, essentially all the energy we receive from the Sun, is the product of
billions of tons of hydrogen, being fused together into helium.
But here on Earth, it's nearly impossible to find.
This is mostly due to the same process, that leads to hydrogen leaking out of the
upper layers of our atmosphere into space, but it's actually much worse for helium.
You see, helium is the first of what we'd call "noble gases".
Meaning, it doesn't really want to react with any other elements to form compounds.
Without being able to form heavier compounds, helium stays an extremely light gas,
causing it to be easily lost into space.
In fact, the only way helium really occurs in our crust al all,
is through the decay of radioactive isotopes, like uranium and thorium.
So technically, birthday balloons are filled with the products of radioactive decay.
Which is actually more rare on Earth than silver.
The 20th rarest element is platinum, while gold is 19th, at 0.005 and 0.004 parts per million, respectively.
Which is strange, because usually in games and stuff, platinum trophies come after gold, as if they're more valuable.
So I looked it up, and at the time of making this video,
platinum is worth 26.51 $ per gram, whereas gold costs 41.23 $ per gram.
So yeah, gold is worth more, and is more rare. I don't know why people seem to think it isn't.
What's cool, is that literally right above these two elements, the 21st rarest element is neon.
Which exists only slightly more than platinum, at 0.0051 parts per million.
That means whenever you see a neon sign, if it actually has neon in it,
it's literally filled with an element equally as rare as platinum on Earth.
But now, we're starting to get into extremely rare elements.
Of the Top 10 rarest element on Earth, exactly 10 of them are radioactive, and that's important.
Because none of these elements have stable isotopes, if given enough time, they will all decay into more basic elements.
Considering that the Earth is roughly 4.5 billion tears old,
all of these elements have had long time to decay, until almost nothing is left.
And actually, at levels this low on Earth, only 4 of these can be reliably measured at all.
Of these measurable ones, radon is the least abundant, at only 0.00000000004 parts per million.
That's so rare, that out of 25 quadrillion atoms, you might only find one atom of radon in the Earth's crust.
But, we still have the lower half of this list, which means there are 6 elements even more rare than this.
The abundance of all of these is so low, that they can only be estimated
using known quantities of other elements, that decay into them.
Within this list is promethium, which is by far the rarest of the so-called Rare Earth elements.
Different isotopes of this element have a half-life ranging from 2 to 17 years.
Which is incredibly short in geological terms.
It there was any promethium, when Earth got its start, it's likely been completely gone for billions of years.
It's estimated, that less than 600 grams of this stuff exists on Earth today.
Most of which was created by the decay of uranium, and maybe a little europium.
But still, we can get rarer.
The rarest element on Earth, with current data, is element 85 - astatine.
Far less stable than even promethium, the most stable isotopes of astatine have half-life ranging from 5 to 8 hours.
But most of its isotopes, and there are 39 total of these, have half-life of just 1 second or less.
That means most of the astatine that exist right now, at this moment, did not exist yesterday,
won't exist tomorrow, and might not have even existed when this video began.
The name astatine comes from the Greek word "astatos", which literally translates into unstable.
That's a pretty fair description of the element, too.
Astatine is so unstable, that we really don't know a lot about it.
Any images we have of astatine, aren't actually of astatine.
What I'm showing you now, is one of the first pictures that show up, when you search "astatine" in Google.
But this isn't astatine, it's a substance called autunite fluorescing under a UV light.
One of the elements that make up his material is uranium.
Which can, on occasion, decay into astatine.
Within this one rock of odinite, there's likely only a handful of astatine atoms.
But that hasn't really stopped people from theorizing, what this element might look like,
using elements we can collect and observe.
Astatine belongs to a group on the periodic table known as the "halogens", which all behave similar to one another.
Halogens then to get darker, the heavier they get.
With chlorine starting out as a light yellow/green, bromine as a reddish brown, and iodine as a darker greyish violet,
it's predicted, astatine would follow in this pattern, and likely be a solid, black metallic color.
But, if enough atoms of astatine were ever collected together for the human eye to see,
the material would immediately vaporize, due to it's own heat produced from decay.
Exactly all of the astatine on Earth currently, is the result of radioactive decay of larger atoms.
Mostly thorium, uranium, and just a little neptunium.
And at any time, it's estimated that less than 1 gram of astatine exists on Earth as a whole.
To put that into perspective: the Earth as a whole, has a mass of 5.972 x 10^27 grams.
Or 5.9 octillion grams, and not even one of them is of astatine.
But humans are pretty smart, and have found ways to artificially produce small amounts of astatine.
By bombarding bismuth isotope 209, with what's called alpha [⍺] particles,
which are basically the nucleus of helium atoms, astatine 209 and 211 can be created in small quantities.
The greatest amount we are typically able to produce at once, is 86 nanograms. Or, 86 billionths of one gram.
Despite its rarity, there is actually one commercial use involving astatine.
Research and experiments using astatine-211 in radio-pharmaceuticals, or "nuclear medicine",
have shown it to be useful as a radioactive tracer, for treating certain cancers.
Although scientists have theorized about other uses, we haven't actually really been able to test any of them out.
That about ends the video. If you enjoyed, well, how about leaving a like?
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Oh yeah, and I've put the full list of elements, from most common to rarest,
in the description with their abundances, if you wanna check that out for yourself.
Thanks for watching, I'll be back next week.