字幕表 動画を再生する 英語字幕をプリント Scientists have thought for a while now that there may be water trapped within the earth's mantle. Yeah, a secret ocean--underneath our oceans--inside the earth! This would change our common understanding of what the earth looks like on the inside. Now, there's new evidence that provides even more support for this idea, and has geoscientists of all kinds wondering how Earth's hidden oceans could have formed. And get this--the new evidence...it's diamonds. Back in 2014, scientists discovered diamonds that contain water-bearing minerals. These diamonds were brought up into human range from deep within the earth's transition zone, around 400 miles below the earth's surface, so this was pretty remarkable. How did water get trapped in something that far down? Well, when we're talking about water here, we're not talking about the liquid water we're familiar with. They're actually the different elements that make UP water--hydrogen and oxygen--bound into the crystalline structure of a solid mineral, which is where we get water-bearing minerals. See, the earth's mantle moves by convection, meaning hot magma rises and pushes other parts of the mantle down further into the earth. When these water-bearing minerals get pushed down because of this convection activity, the increased pressure literally wrings the water out of them--this time, as water we would probably recognize. The initial conjecture that there might be some water deep within the earth was confirmed by the 2014 diamond discovery, and then backed up with seismic data. The seismic readings were consistent with the idea that there was water in the mantle, and it contributes to the mantle's behavior. More recently? Even more diamonds! These new jewels pulled from the earth's depths actually do contain water...but in a TOTALLY new form that we've never observed before. These diamonds, from several locations across southern Africa and China, contain tiny inclusions of a form of water called ice-VII, an extremely high pressure form of water that scientists refer to as water-ice . This is the first time we've ever actually observed this form of water in nature. The researchers say these new diamonds support the presence of, at least what they're calling, 'aqueous pockets' of water throughout the mantle. So not only is there water DEFINITELY inside the earth, but also, it may be in a totally novel form of water. Who knew water came in different forms?!? I feel like that leads us to two important questions: 1.) “So what?” and 2.) “How did it get there?” Well, one answer kind of addresses both. The main theory for how we have water on earth at all is that it got brought to us by rogue asteroids containing water-bearing minerals crashing into us from the far-reaches of our solar system. The theory goes that when the earth was forming, our solar system was probably too hot for any water molecules to survive and cling to the space dust that would become the earth, so water had to have been brought to us from off-planet after the earth formed. But these new diamonds could upend that. Some scientists now estimate that the mantle might contain more water than all the earth's oceans combined, which is way more water than could have been pulled, via convection, from the surface of the earth into the mantle in the given time frame. We may need to re-examine our theories about the state of the solar system at the time the earth was forming--maybe it was possible for water to survive and cling to dust and rock as it coalesced to form the earth. Maybe there's an entirely different theory that we haven't thought of yet! We're still unsure of the exact amount of water in the mantle though, or what form it might be in. Scientists plan to keep exploring, though, both with seismic measurements and lab experiments that try to simulate the materials and pressures that we would find inside the earth. And, of course, keep looking for and examining diamonds--not the kind you want to put in a ring, but of course the kind that contain hydrous minerals. A girl's true best friend. Fun fact: the materials that primarily make up the earth's mantle are called Wadsleyite and Ringwoodite, both water-bearing minerals whose structure leaves them prone to gapping, letting researchers think of them a bit like a sponge that's holding the mantle's water. For more awesome earth science, subscribe to Seeker, and check out this video here about the massive asteroid currently headed for earth.Thanks for watching!