Épisodes

  • Triple North Pole

    Triple North Pole
    Mar 2 2026
    It might surprise you to know there are actually three North Poles: the geographic, the magnetic, and the geomagnetic. The one we most commonly think about is the Geographic North Pole—the tip of the axis that the globe spins around. It’s in the middle of the Arctic Sea, on pack ice, above more than 2 miles of water. During the summer, when the pole is tilted toward the sun, it’s 24-hour daylight. In the fall, the sun finally sets—once, and only once, per year. That brings on 6 months of night, until springtime, when the once-annual sunrise starts another 6 months of day. The North Magnetic Pole is slightly to the south. This is where Earth’s magnetic field, which springs out of the ground at the South Magnetic Pole, dives back into the ground. Its exact location, however, is constantly changing, because Earth’s magnetic field is always changing. Today, magnetic north is moving about 34 miles a year, gradually traveling toward Siberia. Finally, there’s the North Geomagnetic Pole—the northern axis of the magnetosphere, the magnetic shield that protects us from solar winds. If you imagine the magnetosphere as a ball around a bar magnet, with the bar running through Earth, this pole would be the positive end. It’s currently 700 miles south of the Geographic North Pole but also always traveling. With three dark places to look in the dead of winter, and two of them moving, it’s a wonder Santa ever makes it home.
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    2 min
  • Carving a Canyon

    Carving a Canyon
    Mar 2 2026
    The Grand Canyon is so grand it can be seen from space. At more than a mile deep and nearly 300 miles long, it could hold all the world’s river water and still be only half full. And its colossal size is an evolving mystery. Early geologists could not believe such a comparatively small river could carve something so immense. So they looked more closely… And discovered that a myriad of geological processes have combined to form the canyon through time. One of the more dramatic is giant floods, vastly larger than anything we see today. Floods from melting ice sheets. From enormous lakes overflowing their boundaries. From lava dams forming within the canyon, which held back water until they failed spectacularly. Floodwaters can carry hundreds of times more rock material than a normally flowing river. These superfloods likely dragged house-sized boulders through the canyon, battering the softer lower rock layers until they collapsed, bringing all the rock above them crashing down, to be carried away in the next superflood. Geologists suspect these processes happened repeatedly in several smaller canyons, which finally linked together to become the Grand Canyon we know today. In 1919, the U.S. Congress and President Woodrow Wilson set aside the canyon as a National Park for, as Theodore Roosevelt had said years earlier, “your children, your children’s children, and all who come after you.” If you haven’t seen it with your own eyes, you owe it to yourself to go and be awed by the Grand Canyon.
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    Indisponible
  • Homing Pigeons

    Homing Pigeons
    Mar 2 2026
    Since the Roman Empire, troops have used homing pigeons to carry messages from the front lines to command posts. They remained popular for long-distance communication, even after the telegraph was invented in 1844. In World Wars I and II, homing pigeons could operate faster than wires could be strung and farther than the troops’ radio signals. In one famous account, an infantry unit trapped behind enemy lines released three pigeons, but all were shot down. Despite her injuries, one took flight again and successfully delivered her message to save the soldiers. Military surgeons were able to save her life, and she received a French medal of honor and a visit from U.S. General John Pershing. Long ago, homing pigeons were bred from normal rock pigeons, which could find their home from as far as 1,000 miles away. Eventually, handlers realized they could train them to fly between points, by putting their feed at both spots. The birds could even adapt if one of those locations moved. This remarkable power of navigation is partly based on magnetoreception, as we discussed in an earlier EarthDate. But they may also be following anomalies in Earth’s gravitational field, infrasonic sound waves, and scent trails in the atmosphere. The only sense they use that we can experience ourselves is visual. Some studies suggest the birds read surface landmarks like rivers and highways to build their own aerial maps as they fly. It’s yet another remarkable adaptation of life.
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    Indisponible
  • How Earth Makes Fresh Water

    How Earth Makes Fresh Water
    Mar 2 2026
    Earth is mostly covered with water, and most of that is ocean. Only 2.5 percent is fresh water. Of that, 99 percent is locked up in glaciers and underground aquifers. That leaves just 1 percent of Earth’s fresh water on the surface. From all that salt water, how does this tiny fraction of surface fresh water come to be? It’s a process of natural distillation. Heat and wind turn seawater into water vapor. In the phase change from liquid to gas, water leaves salt and all impurities behind. In the atmosphere, water condenses on airborne particles and rains down again. Since Earth is mostly ocean, most rain falls in the ocean. The part that falls on land flows downhill, eventually into rivers that carry it back into the sea, to become salty again. That brief, shining moment as surface fresh water has made virtually all land-based life possible, for hundreds of millions of years. Here’s a practical tip: If you ever find yourself in a dire situation with no fresh water, remember this distillation process. First, never drink seawater; it’s four times saltier than blood. To neutralize it, your organs will draw water from the rest of your body, leading to rapid dehydration. Instead, find a way to make your own cloud. Trap rising water vapor, allow it to condense on a surface, and drain it into something that you can drink from.
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    2 min
  • The Star of India

    The Star of India
    Feb 27 2026
    In October 1964, three young thieves cased the American Museum of Natural History in New York City. They returned that night to scale the museum wall, climb through a bathroom window, and steal 22 of the most precious jewels in the world. Among them were the Eagle Diamond, the DeLong Star Ruby, and, most famous of all, the Star of India sapphire. Sapphires are a variety of corundum, the third-hardest mineral. Pure corundum is clear, but when colored blue by titanium impurities, it’s called a sapphire. When colored red by chromium, it’s a ruby. Mineral inclusions in a sapphire sometimes line up along its crystal lattice to reflect light in a six-pointed star. The Star of India, besides being huge and nearly flawless, has stars that are visible from top and bottom. The thieves didn’t go far with it, renting a luxury apartment near the museum. An informant tipped off the police, who raided the place and captured one of them. The other two fled to Florida; the cops pursued and, a few days later, apprehended them, too—but not before they dispersed the jewels. The Eagle Diamond was never recovered, probably cut into several smaller stones. The philanthropist John D. MacArthur, paid a ransom to have the DeLong Ruby returned to the museum. One of the thieves finally led detectives to the Star of India, which they found with several smaller gems in a wet leather bag in a bus-station locker. It’s Earth’s near-flawless creations that humans still value the most…
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    2 min
  • Green Iceland/Icy Greenland

    Green Iceland/Icy Greenland
    Feb 27 2026
    If you’ve been to Iceland, you know it doesn’t have much ice. In fact, there’s so much grass that on maps it’s colored green. On the other hand, you probably know that Greenland is covered in glaciers. So why is the green one Iceland and the white one Greenland? Legend has it that the Vikings who discovered Iceland wanted to protect it from settlement, so gave it an unflattering name. But it was actually a matter of perspective. The first explorer to Iceland had a terrible trip. His daughter died on the long voyage. He arrived in winter and his livestock froze. That spring, his ship was nearly sunk by icebergs. Fed up, he called it as he saw it: Iceland. And the name stuck. A century later, another Viking explorer was visiting Iceland when he got in a fight with the settlers and was run off the island. He sailed west and found Greenland, which was warmer than today, and the coastal areas were indeed green. Wanting to attract settlers, he called it Greenland. They came, and built farms and grazing operations—which lasted until around 1400, when the climate cooled. Greenland’s glaciers expanded, leaving less green land. Today the Arctic is warming, which means Greenland’s glaciers are melting, and it may one day be greener again. Conversely, cold glacial meltwater entering the ocean from Greenland could blunt the Gulf Stream that warms Iceland, making it icier.
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    2 min
  • Tuskless Elephants

    Tuskless Elephants
    Feb 27 2026
    We often think that evolution takes thousands of years. But in rare cases where humans impact small populations, adaptation can work much faster. Take the case of the tuskless elephant. Nearly all male elephants and most females have tusks. These are just elongated lateral incisors that grow outward once the elephant loses its baby teeth. But a small percentage of elephants are born without these teeth and never develop tusks. In 1919, the South African government brought trophy hunters to the East Cape to exterminate elephants that were eating crops and trampling farms. By 1931, only eight females survived, and half were tuskless—perhaps because they made the least attractive trophies. Instead of natural selection, this was human selection. Fortunately, public opinion forced a change of heart and a preserve was established to protect the elephants. The tuskless matriarchs had tuskless offspring, and today nearly all female elephants in the park lack tusks. A similar thing happened in Mozambique. During a 15-year civil war, soldiers poached elephants for their meat to feed the troops and for their ivory to sell to buy more weapons. Again, elephants with tusks were killed, and by the end of the war, half the females were tuskless. As the population has rebounded, a large portion of females remain without tusks. But with the hunting pressure off, experts think natural selection may again favor animals with tusks—and both groups may eventually become tusked again.
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    2 min
  • The Geology of Fireworks

    The Geology of Fireworks
    Feb 27 2026
    This 4th of July, try regaling your fellow revelers with some firework history and, yes, geology. They’ll probably know that fireworks originated in China. But they likely won’t know they started as simple bamboo sticks thrown into a fire. The air inside the hollow stalks expanded, then exploded, making a “crack” that the ancient Chinese used to ward off evil spirits. A few centuries later, legend has it that a kitchen recipe gone awry combined charcoal, saltpeter, and sulfur. Who knows what food they were trying to make…but they created gunpowder. Warlords quickly recognized its military potential. Luckily, firecracker enthusiasts pursued its celebration potential. They filled those same bamboo tubes with gunpowder, to make a far bigger noise, then used more gunpowder to launch ever-larger firecrackers into the air. And fireworks were born. When Marco Polo came to China, he was so impressed that he took fireworks back to Italy, where they’ve been a hit for over 700 years. The Italians were the first to add common minerals like gypsum and calcite to produce colored explosions. The science has come a long way since, now blending in a variety of metal salts and exotic minerals to make better fuels and to add deeper colors and special effects. So when you see a brilliant finale of red, white, and blue, you can shout, “Wow! Celestine, barium oxide, and copper ore!” Then you can blame EarthDate for making you the science nerd at the party.
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    2 min