Falling Through the Earth Takes 38 Minutes. Here's Every Second.

What would happen if you jumped into a tunnel that went straight through the Earth? You’d fall toward the center, shoot out the other side after about 38 minutes, and then fall right back again. In this video, we follow that journey from Madrid to New Zealand, passing through every layer of the Earth along the way. We’ll look at how fast you’d fall, how hot the rocks get, and what happens to gravity as you travel deeper underground, using a model of the Earth's interior to work out the numbers. We’ll also explore some surprising facts: the deepest hole humans have ever drilled, why earthquake waves suddenly change speed underground, how solid rock can slowly flow, and how a sea of liquid metal deep inside the Earth creates our magnetic field. At the very center lies a solid iron core that's almost as hot as the surface of the Sun. And the journey gets even more interesting when we consider what would happen if the tunnel contained air, how Earth's rotation would affect your fall, and how the same experiment would work on the Moon. Chapters: 0:00 What if you jumped? 0:22 The hole we can't dig 1:17 The crust 2:03 The mantle (gravity gets stronger) 3:07 The outer core 3:53 The inner core 4:22 The center of the Earth 4:44 The other side 5:17 The twists: gravity trains, air, spin and the Moon 6:24 The answer The science behind the numbers All calculations use the PREM model of Earth's interior, assuming a tunnel with no air resistance or friction unless stated otherwise. The deepest hole ever drilled: The Kola Superdeep Borehole reaches 12,262 metres underground, but it's only about 23 cm wide. A standard men's basketball is roughly 23.8–24.8 cm across, so it wouldn't fit. Temperatures at the bottom reached around 180 °C, much hotter than expected, and drilling eventually stopped. In our imaginary fall, you'd pass this depth in about 50 seconds. The crust: Beneath Madrid, the Earth's crust is about 35 km thick. Near the surface, temperatures typically rise by around 25–30 °C per kilometre. You'd cross the boundary between the crust and mantle, known as the Moho, after about 84 seconds, travelling at nearly 3,000 km/h. Andrija Mohorovičić identified this boundary in 1909 after noticing that earthquake waves suddenly sped up as they passed through it. The mantle: This layer stretches roughly 2,900 km beneath the crust. Although it's solid rock, it can slowly creep and deform over millions of years, moving by a few centimetres a year. Temperatures rise from around 500–1,000 °C near the top to about 4,000 K at its base. At 410 km down, the mineral olivine changes into a denser form called wadsleyite. This region may store an enormous amount of water, potentially comparable to an ocean. Deeper down, bridgmanite becomes the dominant mineral. Hot plumes rising from the bottom of the mantle help fuel volcanic hotspots such as Hawaii. Gravity gets stronger:The last full reversal happened around 780,000 years ago. The inner core: At the center is a solid iron-rich sphere about 2,440 km across, roughly 70% of the Moon's diameter. Its temperature is estimated at around 5,400 °C, close to the Sun's surface temperature of about 5,500 °C. The pressure is millions of times greater than atmospheric pressure, and the inner core grows slowly as the Earth cools and material solidifies. What changes the result? A gravity train: Imagine a straight tunnel running 344 km from London to Paris. At its deepest point, it would be only about 2.3 km below the surface. In an ideal frictionless tunnel, you'd reach speeds of around 770 km/h and arrive in about 42 minutes. If Earth had the same density throughout, every straight tunnel connecting two points on its surface would take roughly the same amount of time. Earth's denser core makes the journey through the planet faster, reducing it to around 38 minutes. What if there were air? Air resistance would slow you down dramatically. Instead of reaching incredible speeds, you'd eventually approach a terminal velocity of around 200 km/h under simplified assumptions. The trip would take much longer, and you'd eventually settle near the center rather than emerging on the other side. What if you tried it on the Moon? Assuming a uniform lunar density, the journey would take around 54 minutes, with a maximum speed of about 6,000 km/h. The Moon's average density is about 3.34 g/cm³, compared with Earth's 5.51 g/cm³. That difference in density helps explain why the journey would take longer. One important catch: This is a thought experiment. No real tunnel could withstand the temperatures, pressures and geological conditions deep inside the Earth. Madrid's antipode, the point directly opposite it on the globe, lies in New Zealand. In fact, only around 15% of Earth's land has land directly opposite it. #earth #physics #science #infospark #nasa