(computer phone ringing) - Hi, it's Doug. I recently moved to Austin, Texas, and there's so many new things I'm looking forward to checking out. Now, I moved here during the
summer when it's really hot so one thing I'm really looking forward to is visiting a swimming hole. Texas is famous for its swimming holes. These are naturally
occurring pools of water, usually connected to an
underground cave system. Like check this out. This swimming hole is called Jacob's Well. You notice how dark it looks? That's because the bottom
is over 140 feet down, but I've heard that that
water feels nice and cool on a hot day. Someone named Brayden has
a question about holes in the earth. Let's give Brayden a call now. (computer phone ringing) - Hi, Doug. - Hi, Brayden. - I have a question for you. What's the deepest hole
anyone has ever dug? - Ooh, that's a great question. People have been digging
holes for a long time and for a lot of different reasons. (fox yelling) (jolly music) Some people dig holes just for fun like this person named Ra Paulette. He's been digging holes for over 25 years, but not just any holes. Check this out. Isn't that incredible? These holes he digs by
carving into a soft type of sandstone rock are
beautiful works of art. The amazing thing is he
digs them all by himself with no tractors or machines to help. Some of them, like this one,
are even homes you can live in with a bathroom and kitchen, so cool. But people don't only dig holes for fun. Thousands of years ago,
people dug holes to live in like the builders of this city in Turkey. It's called Derinkuyu
and it's the deepest city in the world. It's located as deep in the ground as a 20 story skyscraper is tall. No one lives down there
now, but a long time ago, it could hold 20,000 people. Now, even though Derinkuyu is pretty deep, it's not even close to
being as deep as this hole. This is the deepest hole
anyone has ever dug by hand without the help of any machines. It's 1,285 feet deep. That's deeper than the
empire state building is tall and it wasn't easy to dig. The deeper the workers
dug, the darker it got, and they only had
candles to light the way, but they kept digging day
and night for four years until finally they found
what they were looking for. Can you guess what it was? Water. The hole is called the Woodingdean Well and it was dug to find water to drink. See, there's actually a lot
of water under the ground, 100 times more water than all the rivers and lakes put together. So where water is needed, people dig holes to try to find it. But water isn't the only thing
you can find when you dig. Sometimes people also dig holes
to find valuable resources like silver or gold. That's what these miners in
South Africa are looking for. The Mponeng Gold Mine is the
deepest mine in the world. It's as deep as 10 empire state buildings stacked on top of each other. This hole is so deep, it
takes miners over an hour on special elevators just
to get to the bottom. And once they're down there, it's hot. At 140 degrees, it's
hotter than the hottest day ever on earth. That's because the deeper
you dig, the hotter it gets. Before I go on, I'm curious. Besides looking for water or
valuable resources like gold, what are some other reasons
you think people dig holes? Now would be a good time to
pause the video and discuss. Okay, you ready? Well, I'm not sure how you answered, but you may be surprised to
hear that the deepest holes on earth were dug because
people were just curious. They wanted to know what they
might find way, way down, deep in the earth. Like this group of scientists in Germany. They were trying to
reach a mysterious layer inside the earth called the mantle. Using special drills,
these scientists were able to dig a hole that went
almost 30,000 feet deep. Now that's deeper than the
world's tallest mountain, Mount Everest, is tall. It's called the KTB Borehole and it's the second deepest hole ever dug. But even though they dug pretty deep, they weren't able to reach the mantle. They did leave the hole open
for people to visit, though. If you're ever in Germany,
you can check it out. If you think that's deep, remember, I said that was the
second deepest hole ever dug. This is the Kola Borehole in Russia. It is the deepest hole on earth. Using special drills,
workers dug for over 20 years and they got pretty far,
seven and a half miles down. That's deeper than 30
empire state buildings stacked on top of each other. But don't worry, it's only
about as wide as a dinner plate, so there's no way you can fall in. So were they able to reach the mantle? Not even close. In fact, if the earth were
the size of an orange, then the Kola Borehole
wouldn't even go past the peel. But why is that? Are the drills we use to
dig just not long enough? Even though that makes sense, making long enough
drills isn't the problem. The problem is heat. See, the closer you get to the
mantle, the hotter it gets. It's so hot down there that normal drills can melt like ice cream
when they go that deep. And it's not just the
drills that melt down there. The rocks down that deep
in the earth are so hot that they start to act almost
like a thick, gooey liquid, almost but not quite as hot as lava. So it doesn't look like
we'll be digging a hole all the way to the other side
of the earth anytime soon. Still, scientists are
curious to figure out if there are new ways to dig even deeper. If this is something that interests you, maybe it's something you'll
help figure out one day. But until then, it's
important to know that digging deep holes on your own can be dangerous, so if you do try to dig, never dig a hole that's
deeper than you are and make sure you always have
an adult nearby to supervise. That's all for this week's question. Thanks, Brayden, for asking it. Now, for the next episode, I reached into our question jar and picked out three questions sent into us that we're
thinking about answering next. When this video is done playing,
you'll get to vote on one. You can choose from, "How
were Lego bricks invented?" "How does it compass
know which way is north?" Or, "What is in food coloring?" So submit your vote when the video's over. We want to hear from all of you watching. There are mysteries all around us. Stay curious and see you next week.
