There's a region of our planet that no human being has ever visited. No one has ever seen this place, yet what happens here affects every one of us every day of our lives. It's 2,000 miles beneath our feet – the Earth's molten core. Here, a vast ocean of liquid iron generates an invisible force – the Earth's magnetic field. It's what makes our compasses point North. But it does a lot more. It helps to keep the Earth a living planet. Our neighbors Venus and Mars have only weak magnetic fields, which means they're unprotected from the deadly radiation sweeping through the solar system. The Earth, on the other hand, exists within a vast magnetic cocoon – a force field that, for billions of years, has sheltered us on our journey through space. But now, scientists have made a startling discovery. It seems there's a storm brewing deep within the Earth – a storm that is weakening our vital magnetic shield. The Earth's magnetic field has been our protector for millennia, and now it appears it's about to go away. Yes, the magnetic field is getting weaker rapidly. We cannot guarantee the magnetic field of the Earth is still going to be there if I wasn't here from today. Is our invisible shield about to disappear? The question is not if that's going to happen, it's when that's going to happen. Could the Earth really lose its magnetic field, and what will happen if it does? Up next on Nova, magnetic storm. Major funding for Nova is provided by the Park Foundation, dedicated to education and quality television. We see 400 employees in three years at Microsoft, your potential inspires us to create software that helps you reach it. Your potential, our passion. Science, it's given us the...