Then the geologists got to the sea floor. One of the many unexplained phenomena of the Earth’s structure was that several oceans had ridges of underwater mountains running in vast lines across the flat plains of the ocean floor. No one knew what they were doing there. The most famous is the mid-Atlantic ridge, a line of volcanoes that starts above water (the country we call Iceland is just the protruding end of this ridge) and then disappears underwater, where it zigzags all the way down the center of the Atlantic Ocean almost to Antarctica. Then, in 1960, magnetic measurements showed that the magnetism of the rocks surrounding that ridge was very strange indeed. It was striped, and the stripes ran parallel to the ridge. As you went away from the central ridge, the sea-floor rocks had magnetism that pointed north, then south, then north again, and these stripes ran the length of the mountain range. And it got weirder. If you looked at the other side of the ridge, the magnetic stripes there were an exact mirror image.
In 1962 two British scientists, Drummond Hoyle Matthews and Fred Vine, made the link.?? With hindsight, you can almost hear the solid “click” as all the strange pieces of geology dropped into place. What if, they said, the sea-floor volcanoes are building new sea floor as the continents move apart? The magnetism at the ridge lines up with today’s magnetic field. But as the continents move apart, that rock from the ridges is carried out to both sides of the volcanoes and new rock is made. When the Earth’s magnetic field reverses, the magnetism of the new lava will also reverse, starting a new stripe that points in the opposite direction. The reason the stripes are a mirror image of each other is that each stripe represents a period of one magnetic alignment, before it flips back the other way. Other discoveries around the same time showed the places where old sea floor was being destroyed, which was important because the planet itself stays the same size. On the other side of South America, the Andes mountain range exists because that’s where old sea floor from the Pacific is being pushed underneath the continent, back down into the Earth’s mantle. Once you know that the continents can be shunted around, colliding and separating, creating and destroying sea floor as they go, the patterns of geology make sense. This was the seminal moment in geology, the discovery of plate tectonics. Plate tectonics is now the backbone of everything we understand about why the Earth is the way it is.
So the continents do drift, but they don’t plow through the sea floor. They float on top of what’s underneath, pushed around by convection currents beneath the Earth’s surface. And this process isn’t just something of the past. The Atlantic Ocean is still getting wider today, by about 1.5 inches per year.## Today’s magnetic stripe is still being built. It took an astonishing bit of evidence to convince scientists that the surface of the Earth could possibly be so mobile, but the sea-floor magnetism patterns make it undeniable. Today we can measure the movement of all the continents using very accurate GPS data, and we can see the engine in action. But the key to the Earth’s past history and present shape was in the magnetism that can be locked into the planet’s rocks for millennia.
Electricity and magnetism together form a partnership that is incredibly important to us. Our own nervous system uses electricity to send signals around our bodies, our civilization is powered by electricity, and magnetism lets us store information and marshal the tiny electrons that get things done. So it’s striking that our civilization has done so well at keeping the world of electromagnetism under wraps. We rarely experience electric shocks or power cuts, and we’re so good at shielding ourselves from magnetic and electric fields that we could live life hardly knowing that they’re there. It’s both an amazing endorsement of our control of electromagnetism, and extremely sad because we are hiding this extraordinary part of the world away from ourselves. But maybe the future will hold some extra reminders, and we won’t forget it completely. As our civilization faces up to its addiction to fossil fuels, one way out seems to be becoming more likely. Power generation won’t just happen in remote power stations. Renewable energy can be generated much closer to home, and maybe in the future, we’ll see more of where our electrical energy comes from. The face of my watch is a solar panel, and the watch has been running continuously for seven years now. Technologies already exist that will harvest solar energy from our windows, kinetic energy from our footsteps, and wave energy from our estuaries. And the principles that they’re based on are just the principles of electromagnetism.
THERE IS ONE last piece to the electromagnetic pattern. We saw that an electric current could generate a magnetic field in the toaster. But that process also works the other way around. When you move a magnet near a wire, it pushes on charged particles like electrons, and that means that you can create an electrical current that wasn’t there before. This isn’t just relevant for the future; this is what makes our electricity grid possible now. We can only get energy into our electrical grid by moving magnets around, whether by using turbines in gas-fired or nuclear power stations, or by turning the handle on a wind-up radio. One of the most beautiful and simplest examples of using electricity and magnets to power our world is the wind turbine.
A wind turbine looks serene from the ground, a soaring white strut supporting elegant twirling blades. But the peace is broken the moment you step inside the base of the tower. The innards are filled with a deep, loud hum, and you realize you’ve stepped into the belly of a giant musical instrument. The one I walked into, in Swaffham in the east of England, is one of very few that have regular visiting hours, and it’s more than a little way off the beaten track. But it is absolutely worth the trip.
As you climb the spiral staircase inside the tower, you climb through the hum as it rises and falls. You can feel the structure being buffeted by the wind. You know that you’re getting close to the top when the light starts to flash—natural sunlight is being cut out as the blades rotate. And then out you pop, into an enclosed 360° viewing gallery at a height of 220 feet, right underneath the turbine hub. Any sense of serenity is now long gone. The three gigantic blades, each 100 feet long, are whooshing around with considerable oomph and there is no doubt that there is energy up here to be harvested. As the wind rises and falls, the whine and the blade speed respond almost instantly. This alone is impressive enough.