Hello and welcome to SciShow news, where this week we bring you discoveries involving two of the most exotic substances on Earth: The world's rarest element, and the world's oldest water. I bet they taste great together.

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World's Oldest Water (0:16)

I know, you're probably thinking that there's nothing less exotic in the world than water, we do have a ton of it. But on Wednesday, a team of British and Canadian researchers said that they've discovered what may be the oldest water system in the world.

It was found in a mine two and a half kilometers under Ontario, Canada, and it is at least 1.5 billion years old, though it could be much, much older than that.

To give you some perspective on how long ago 1.5 billion years is, that's when the first multicellular life was first starting to blink into existence. I'm talking like way before even the first Doctor in Doctor Who, if that helps you with the age in history. And according to Thurday's issue of the journal Nature, even though this water has been locked away from the sun, the atmosphere, and living things for all that time, it contains an ideal chemical cocktail for supporting life.

See, almost all water on Earth goes through a cycle of precipitation and evaporation, it's called the hydrological cycle. This is not only how water moves from one part of the planet to another, it's also how organic compounds and minerals necessary for life circulate.

But water trapped deep underground gets isolated from this cycle. That's why while other isolated pockets of water have been discovered that are really old, none of them could sustain life. But this water is different.

Unlike those other pockets, which were basically small underground bubbles, this is a big system, and it flows. And as it moves, the water interacts with the rock that surrounds it, and dissolves it into smaller compounds, and as a result, the newfound system has a chemistry that's very similar to that found at deep-sea thermal vents; rich in dissolved gases like methane that can be used for energy by microbes that don't have access to sunlight, plant life, or any other energy source.

Extraterrestrial Life (1:49)

The researchers are now looking for organisms in the new water system, but they're already saying that just like deep-sea vents in underground lakes in Antarctica I've told you about, this stash of billion-year-old water is further evidence that life on other planets could be well below the surface. Mars, Europa, I'm looking at you guys. So this discovery may not just change how we look at life on Earth, but how we look for it on other worlds.

Kicking Astatine (2:12)

Now, if that chemistry wasn't exotic enough for you, well, there's something wrong with you. But perhaps then I can interest you in some astatine, the rarest naturally occurring element on the planet, and this week, chemists said that they finally figured out one of its most fundamental properties.

Specifically, they've determined astatine's ionization energy, or ionization potential. That's the amount of energy required to remove an electron from one of its atoms. That is, to turn an atom of it into an ion, and that's one of the basic things that we know about pretty much every element on the periodic table.

Why At is Where it's At (2:41)

But astatine's has taken us forever to figure out. Discovered in 1940, the element only occurs on Earth as the result of the radioactive decay or other elements, like uranium and thorium, and its most stable isotope has a half-life of only about 8 hours. And it can't be seen with the naked eye, because any mass big enough for you to see would vaporize itself and maybe you, and everything around you, from the heat generated by its own radioactivity.

So yeah, pretty hard stuff to study, but at least we know that it's awesome. I mean, in addition to vaporizing itself, for instance, we might be able to use it to vaporize cancer. Because astatine emits enormously strong radiation in a really short range, it can be precise in its awe-inspiring destruction, killing cancer cells without damaging surrounding tissues. Scientists have been looking into this kind of therapy called targeted alpha therapy for several years. 

The discovery of astatine ionization energy is one more step towards understanding how it reacts in different environments, like inside the human body. So one of the last blanks has been filled in our understanding of the natural elements, and yet another clue has been found to finding an effective treatment for cancer. The research appears in Wednesday's issue of the journal Nature Communications.

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