The Hole Truth About Digging Down
Normally in an Isaac Arthur video he would talk about humanity going somewhere outward like orbit, a neighboring planet or a far away star. Presumably that's why some of his videos are grouped in an "Outward Bound" series. This video though explores going down under the Earth's crust.
Billions of years ago as the Earth was forming the planet was completely molten rock. As the Earth's top layer cooled the more dense rock sunk down toward's the center of gravity (the core). Many of the heavier elements in the sinking rocks were also radioactive and the atomic decay is one of the factors keeping the rock deep under the Earth's crust continuously molten.
If humans could successfully drill down past the first few dozen kilometers of the Earth's crust there would be more access to metals and energy in the form of geothermal heat. It's really hard to drill down, as the video points out, without massive effort. There are theoretical methods the video describes but logistically going to the asteroid belt for metals and harnessing more solar power is relatively easier.