What If You Just Keep Digging?

If you've ever thought, "what if I just dug  a really really deep hole? ", that's what the USSR did right here! That hole is deeper than the  deepest part of the ocean.

It's deeper than Mount Everest is tall. They started digging it in the  1970s as part of basically a space race but down the United States only got to 600 ft before  pulling funding but the USSR kept going for 20 years. They made it about a third of the way  through Earth's crust and then stopped.

But what if you just. . .

kept. . .

digging? If you dug a hole all  the way to the center of the Earth, what would you find? What would happen to you?

And what does our  newest tech tell us is really going on down below our feet? "Let's take a look at what's inside! " "to the  center of the Earth" "went where no human being had ever set foot" "still falling!

" "the center of the Earth"  "the heat and the pressure" "what's underneath the Earth's crust is different" "the deeper you go into  the Earth the hotter it gets" "that's wild! " Imagine we go outside and we just start digging.  At about 50 m deep we might start to feel the temperature go up.

Every kilometer through the crust is about 25 C hotter. Right now, we're inside the crust. On land, it's typically less than 40 km deep which is less than the length  of a marathon.

We're passing through soil and layers of hard rock past precious metals and  fossils and as we get deeper we start to see all kinds of impressively deep things that  people have built like there's the Kamioka and Sanford research Labs that do dark matter and  neutrino physics research or there's China's insanely deep nuclear command bunker. There's  the deepest cave we've ever discovered plus some of the deepest mines in the world. As we  go deeper, temperature and pressure continue to rise but by this point, unprotected just in  the Earth, we were crushed and crispy a while ago.

To go farther, let's equip ourselves with an  imaginary drilling machine that's immune to any temperature or pressure. Now finally at 12. 2 km  we reach the deepest point humans have ever dug this is that hole the USSR dug the Kola Superdeep Borehole.

They didn't put any humans down here this equipment was operated remotely. To  get so deep, these scientists had to invent new equipment and drilling methods to pierce through  the thick hot pressurized rock. Along the way they discovered new fossilized organisms dating back  2 billion years years and found there was water much deeper than scientists previously thought. 

We actually emailed three of the scientists who worked on this project and one of them told us  "the Russians tried several times to get down past the maximum depth that they had reached  but each time the New Hole tended to collapse. " This was a "moonshot which will never be repeated or  surpassed. " This is so cool but the craziest part is this deepest hole that humans have ever dug  is only .

2% of the way to the center. Time to go deeper. At about 30 to 50 km down, we noticed that  the rock around us is changing.

We're crossing into the mantle. At first the rock around us looks  really brittle, like the crust but denser. But as we get a little deeper as the temperature rises  over 1300° C, something weird starts to happen the rock around us starts to look like hot plastic. 

Here, the temperature is higher than the melting point of the rock but the pressure is so high that  it's still keeping the rock solid. It's gooey. We're now starting to push through even hotter material. 

It's slowly inching from the bottom of the mantle toward the top in these giant convection currents  over millions of years. And you might be wondering, why is the earth hot? Well it's partly radiation  and partly leftover heat from when the Earth formed by meteorites smashing against each other  over and over again.

The Earth is cooling very very slowly but we don't need to worry about that, it's  going to take billions of years. In the meantime this stirring of hot goop brings enormous amounts  of heat from the center toward the crust. But hang on.

. . how do we know that?

If humans have only ever  been 12 km down how do we know that? "Yeah that's a great question. " That's DrMegan Newcombe, a geologist  and vulcanologist at the University of Maryland.

She told me that studying the deep Earth is like  being a detective. "We can't get there so we have to put together all of these indirect pieces of  evidence to work out what's going on down there. " Ancient scientists had a lot of theories about  what was going on down there.

Some thought the Earth contained a central fire with underground  lakes and lava chambers. Some thought it was hollow, maybe a set of concentric shells with life on each  ring. This is the basis for the "Hollow Earth" in the Godzilla movies.

Isaac Newton suggested that based  on observable gravity, the stuff in the center must be denser than the stuff at the top. But it wasn't  until the early 20th century the scientists could prove that the Earth had a central core and there  were several different layers above it. These breakthrough discoveries were thanks in large part  to earthquakes.

During an earthquake, we feel it up here, but it's also sending seismic waves down.  "They are just like sound waves but there are two main varieties: There's P waves and S waves. " P waves  can travel through liquids and solids but S waves can only travel through solids.

They also behave  differently depending on the density of the rock that they're moving through. Which means that by  measuring what waves end up at different detectors all over the surface, scientists can understand  what's going on between them. That's one big way that we've learned about how the mantle differs  from the crust and it also taught scientists something else: "We find this S wave shadow on the opposite  side of the planet that tells us that for some reason the s-waves couldn't propagate all the  way through the Earth and that tells us that there's a liquid layer down there.

" That liquid  layer is part of what we now call the outer core. We've now crossed into a liquid soup  of metals cooking at around 4,400° C. Here temperature has won the fight against pressure  and we should all be extremely grateful for the hot metal soup down there because its constant  churning generates enormous electric currents which in turn create the magnetic field around the  Earth.

And without that, cosmic radiation would just end all life as we know it on the surface. But  this gets weirder: Our magnetic field sometimes actually just reverses. The North and South  poles slowly swap places.

And we know that because. . .

"you can actually read off all of those  magnetic reversals on the ocean floor. " Yeah! "As basalt is erupted along our mid ocean ridges, it  freezes in a record of what the magnetic field was at that time and as the plates continue to  get created and pulled apart, we can read them off like a barcode.

" So what you're telling me is  there's a barcode for our magnetic fields at the bottom of the ocean and scientists have learned  to read it? "Mhm! " Excellent.

You can read this too: it flipped here, it flipped here, it flipped here.  The last reversal was around 780,000 years ago. When will it flip next?

We're not sure! But I  had a much more basic question about all of this: Why is the earth in layers? "You're going to  like this one: At the beginning we were a magma ocean.

The entire Earth was molten liquid. During  that time the densest materials which are the iron metal sank and formed the core and then  the lightest minerals floated to the top and the densest minerals settled to the bottom and so  we've segregated by density. " Okay we've almost made it through all of those layers we are deep  inside the Earth's outer core and then you hit something.

Hang on though if you're going on a  real life adventure, you might want to take this. This is my water bottle, this is the Larq PureVis  2 and what's cool about it is that when I press this it's purifying the water inside. It uses  UV light to break down the chemical bonds of bacterial DNA specifically ecoli and salmonella. 

That keeps the inside clean compared to a water bottle without that. In this example here they  swab the inside of two water bottles used for 4 weeks, Larq is on the left and a water bottle  like the one I used to have is on the right then they waited to see what bacteria grows from  each and. .

. the PureVis 2 also has a plant-based filter that removes pollutants so better taste, healthier  water. Plus and this is my favorite part it helps me remember to drink enough water.

This is my real  data from the last week, you can see I'm hitting my goal almost every day. The way this works is  it has a little sensor in the cap that measures the water level inside after each sip so I get  real-time insights on my progress. The light ring on the cap will light up to remind me to drink  water and you can set the frequency of that in the app so I have mine set to every hour and it  has a double wall insulation that keeps water cool for 24 hours.

If you want to check it out  there's a link in my description. Now back to the story: At the very center of our planet there is  a solid metal ball that's almost as hot as the surface of the Sun and for a long time we didn't  know it was there. We assumed that everything in the core was molten because why would it be solid? 

But then these two scientists were studying more of those seismic waves and they noticed that when  those waves got to the center they started to act weird! Waves were being bent and reflected by  something in the middle. The math only made sense if there was a solid core inside the larger  liquid one.

Other scientists confirmed this theory with more precise recordings of the waves better  computational models. So why is it solid? Well it turns out that the pressure here is so insanely  high that the iron atoms literally can't move and what's even stranger is that more recently  scientists have found slight discrepancies in the data that seem to show Earth's core is rotating  at a different rate than we are at the surface and that rate changes.

It is speeding up and slowing  down separately from what we're doing up here because why not! Very precise seismic data and  computer models of our magnetic fields show that the Earth's inner core seems to be speeding  up and slowing down on a roughly 70 years cycle you might have seen headlines that the earth's  core is reversing but that's not true. It's just that if you were on the outside of the inner  core and I'm on the surface it would look to me like you were going the opposite direction if  you're slowing down even if we're both moving the same direction.

But this iron core is no match  for our magical digger. We are going straight through it until finally we did it. We made it  to the very center.

We are now 6,400 km from the surface the pressure around us is 3. 6 million  times what it is on the surface. But in lots of ways what's around us right now is still a big  mystery.

Like is there an inner inner core? Some scientists think that there might be there's  new seismic data that suggests that the iron atoms are packed differently way on the inside  but others aren't so sure that that's enough to call it a new layer we've been wrong before but  we're becoming better detectives. Can we predict the Earth's magnetic field and when it might  flip?

Scientists are building experiments that mimic the inner earth to learn more. Now the  cutting edge is finding new ways to analyze seismic waves with better computational models  and even finding ways to replicate the deep Earth conditions here on the surface. We are a  curious species locked on the outside of our own home and we're doing everything we can to peek  inside.