00:00We have sent humans to the moon and robots to Mars, but did you know we have barely scratched
00:04the surface of our own home?
00:06Even though we live on the Earth, the center is actually one of the most mysterious places
00:11in the solar system.
00:12You might think we could just dig a hole to see what is down there, but the first big
00:16question we have to answer is, why can't we just drill to the center?
00:20The answer is that we have tried, and it is much harder than it sounds.
00:24The deepest hole humans have ever drilled is called the Kula Superdeep Borehole in Russia.
00:28It took 22 years to drill down about seven and a half miles, which sounds like a lot,
00:33but that is only 0.19% of the way to the center.
00:37At that depth, the heat was so intense that the rocks started acting more like plastic
00:41than stone, and the hole kept collapsing because the rock was so squishy.
00:45If we tried to go all the way, the temperatures would reach nearly 10,000 degrees Fahrenheit,
00:50which is about as hot as the surface of the sun.
00:53This heat would melt any drill bit made of any material.
00:56We currently know how to build, plus the pressure down there is 360,000 times stronger than what
01:02you feel at sea level, which would crush any equipment instantly.
01:05So if we can't dig there, how do we actually know what the core looks like?
01:09The secret lies in using earthquakes as a giant planet-sized ultrasound.
01:13Whenever an earthquake happens, it sends shock waves through the entire planet.
01:17Scientists use machines called seismographs to listen to these waves as they travel through
01:21the Earth and come out on the other side.
01:23This leads to our next big question, how do these waves actually show us the layers if
01:28we can't see them?
01:29Well, there are two main types of waves we look at, called P waves and S waves.
01:33P waves are fast and can travel through almost anything, whether it is solid rock or liquid
01:38metal.
01:38But S waves are very picky and can only travel through solid material.
01:42Seismologists notice a massive mystery.
01:44When an earthquake happens, the S waves completely disappear when they reach a certain death.
01:48This created a shadow zone on the opposite side of the planet, where the waves just couldn't
01:52reach.
01:52This told scientists that there must be a giant layer of liquid blocking, the S waves, which
01:57is how we discover that the outer core is actually a sea of molten metal.
02:01But then does that mean the entire center of the Earth is just a liquid puddle for a long
02:06time?
02:06That is exactly what people thought.
02:08But in 1936, a brilliant scientist named Engleman noticed something strange in her data.
02:13She was a pioneer who used to organize her earthquake requires in oatmeal boxes because
02:18computers didn't exist yet.
02:20She saw that some P waves were bouncing off something in the very center and showing up in
02:24places they should not have been.
02:26She realized there had to be a solid ball of metal right in the middle of all that liquid.
02:30This is the solid inner core, a ball of iron and nickel, about the size of the moon.
02:35Even though it is hot enough to melt, the pressure at the very center is so high that the metal
02:39is forced to stay solid.
02:41But wait, how do we now for sure it is made of iron and nickel if we have never seen
02:45a
02:45piece of it?
02:46This is where things get really cool, because some of our best evidence actually comes from
02:50outer space.
02:51Our next question is how what do space rocks have to do with the Earth's core?
02:55Scientists study materialites, which are like the leftover building blocks from when the
02:59solar system was first made.
03:00Some materialites are made of almost pure iron and nickel.
03:03We believe these are the actual cores of baby planets that were smashed apart billions of
03:08years ago in giant space collisions.
03:10Since Earth was made from the same ingredients as those other planets, it makes sense that
03:14our core would be made of those same heavy metals that sank to the center while the planet
03:19was still molten.
03:19Finally, you might ask, is there any other way to prove that all this moving metal is actually
03:24down there?
03:24The answer is all around you right now, in the form of Earth's magnetic field.
03:28The liquid outer core is constantly swelling, and because it is made of metal that conducts
03:33electricity, it acts like a joint generator called a geodynamic.
03:36This movement creates the magnetic field that protects our planet from space radiation and
03:40makes your compass work.
03:42Without a liquid metal core, we wouldn't have a magnetic field, and Earth would have lost
03:46its atmosphere a long time ago, looking more like the dry, dead surface of Mars.
03:50It is pretty amazing that even though we have never been there, we can use mad earthquakes
03:54and space ropes to map out the heart of our planet.
03:57So the next time you use a compass or look at a map, just remember you are feeding the
04:01effects of a giant metal engine, spinning thousands of miles beneath your feet.
04:20One of the things that you use a lot is to really make of an ice depth and your heart
04:22rate.
04:22It is a very easy that you have to legitimate inner Getting Ahead, as you can see in the
04:22way through the next steps, and you can see a muscle작 that just can be done by clicking on.
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