Kola Superdeep Borehole: The deepest hole ever dug by humans, reaching approximately 12.2 km into the Earth's crust. It was part of a Soviet research project. Seismic waves: Waves of energy that travel through the Earth, generated by events like earthquakes. There are two main types: P-waves (can travel through solids and liquids) and S-waves (can only travel through solids). Scientists use these waves to study the Earth's interior structure. P-waves: Seismic waves that can travel through both solid and liquid materials. S-waves: Seismic waves that can only travel through solid materials. Mantle: The mostly-solid, rocky layer of the Earth between the crust and the outer core. It's composed of silicate rocks. Outer core: The liquid layer of the Earth's core, composed primarily of iron and nickel. Its convection currents generate the Earth's magnetic field. Inner core: The solid, innermost layer of the Earth's core, composed primarily of iron and nickel. It's solid due to immense pressure despite high temperatures. Earth's magnetic field: A magnetic field generated by the Earth's outer core, which protects the planet from harmful cosmic radiation. Magnetic reversal: A phenomenon where the Earth's magnetic poles switch places. Evidence of past reversals is recorded in the ocean floor's basalt. Magma ocean: A hypothetical early stage in the Earth's formation where the entire planet was molten. Convection currents: The movement of fluids (like the Earth's mantle) caused by differences in temperature and density. Hotter, less dense material rises, while cooler, denser material sinks. UV light: Ultraviolet light, a type of electromagnetic radiation used in the Larq PureVis 2 water bottle to purify water by breaking down bacterial DNA. E. coli and Salmonella: Types of bacteria whose DNA is targeted by the UV light in the Larq water bottle. question." that's Dr. megan 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 This segment details the Kola Superdeep Borehole, the deepest hole ever dug, highlighting the challenges faced and discoveries made during its creation. It then transitions to a description of the Earth's layers, explaining the transition from the crust to the mantle, the changes in rock composition and temperature, and the role of convection currents in heat transfer. The segment emphasizes the limitations of human exploration and the use of indirect methods to understand the Earth's interior. 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