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Microscopes, telescopes and lenses. Smartphones, laptops and televisions. Mirrors, windshields and cathedral windows. None would be possible without glass. It’s made of silicon dioxide, or quartz, that’s melted and then cooled so fast that crystals can’t form, which gives glass its most important quality today: transparency. But glass was first valued for the way it breaks. Early humans found naturally occurring glass— from volcanoes or when a meteor superheated desert sand—and used its broken shards to cut things or make weapons. Not too much later, humans learned to melt sand to make glass. They added metal salts to make different colored glass for jewelry and to adorn metalwork. Soon, different cultures were blowing glass to make colored plates and vessels. But it wasn’t until the industrial age that glass assumed today’s roles. Transparent, inert, sanitary, and weatherproof, glass made windowpanes, bottles and jars, chemical beakers and electrical insulators. Each year, its uses expanded. Using complex manufacturing and exotic additives, modern glass can withstand bullets or atmospheric reentry; form supersharp microscopic blades; make fibers that can be woven into building insulation; and so much more. Clearly, our lives would be pretty dull without glass.

In 1836, Charles Darwin and his colleague Joseph Hooker visited Ascension Island, really just a barren pile of volcanic basalt topped by an old cinder cone, ironically named Green Mountain. There were very few plants, but some soldiers had successfully grown a vegetable garden in the volcanic soil. This gave Hooker a crazy idea. He contacted his father, the director of the botanical garden in London, and persuaded him to send plants. Hooker and Darwin believed that if they could establish a thriving plant colony on the island, it would trap water and self-perpetuate. By 1850, the Royal Navy had brought dozens of species from Europe, Argentina and South Africa. Just 20 years later, Hooker and Darwin were proved correct. The plants thrived and still do today. Near the coast there are now grasses, shrubs and mesquite. Higher up the slope, cactus and acacia trees grow in the increasing moisture. Above 2000 feet, the island becomes a misty cloud forest of ferns, eucalyptus, bamboo and evergreens, with food crops like fruit trees, coffee and ginger. A water catchment system built long ago is no longer needed since the island makes its own wet microclimate. Green Mountain is now in fact green—a signal that similar efforts, in places with the right potential for rainfall, could regreen other barren landscapes—maybe even on other planets!

Fireflies are sometimes called lighting bugs or glowworms. But they’re not flies, bugs or worms—they’re beetles, with a marvelous capability. They move oxygen through a tube in their abdomen to combine it with a special pigment called luciferin to produce bioluminescence, the familiar glow that gives fireflies their name. There are 2,000 species of firefly around the world and 170 in the US. Different species produce different colored light, from bright red to fluorescent green. And they flash their light differently too. Males of some species blink their own unique message, hovering a few feet in the air, signaling to females on the ground, who flash back. When the language is right, the male flies down to the female to mate. In different species, the males synchronize their flashing, all sending the same message at the same time. It’s thought that this brighter light gives females a better look at their suitors. Once mated, the females lay eggs. The larvae grow underground, then the immature beetles crawl around in leaf litter, eating worms and slugs, before they mature and take flight. If you’d like to see fireflies around your house this summer, provide a good environment. Don’t spray pesticides, which kill fireflies and other beneficial insects. Allow the grass to grow longer and leave some leaf litter around trees. Then keep your outside lighting low: a dark yard will invite fireflies to flash their unique language of love.

Scientists have a new way to measure rain, or rather, rain intensity. They looked at data from 185 weather stations across the globe, from 1999 to 2014, to determine how much rain fell in how many days. They found that, on average, one twelfth of an area’s rain falls in its single wettest day, one eighth in its wettest 2 days, and half in just 12 days. They decided to standardize this metric—the number of days it takes for half the rain to fall—as a way to gauge rain intensity in an area. This is important because it’s intense rain that overwhelms the soil‘s capacity to absorb water, or the ability of a drainage system—of storm sewers, creeks and rivers—to carry water away, leading to floods, landslides and other impacts. Scientists then projected what a warming atmosphere might mean to rain intensity. Since warmer air can hold more water vapor, we could see more rain overall. This might be good news for places that don’t get enough rain. But in already rainy areas, the increased rainfall may occur within its highest intensity rain days. The single wettest day could see 20 percent more rainfall. This could occur while population, and the cost of infrastructure, continue to rise in coastal cities around the world, putting more people at risk of flooding, with more need for better flood warning and management.

We’re all familiar with those violent shaking events we call earthquakes. But it may surprise you to know that Earth more often moves without quaking in what’s called a slow or silent slip. It sure surprised scientists: they discovered this just 20 years ago. Earth’s tectonic plates began to move over a billion years ago. Their constant motion has formed, pulled apart, and slowly destroyed continents for millennia. Each tectonic plate rotates around an axis, while its edges collide with, slide over, or subduct under other plates. While some of this movement occurs in dramatic releases of stress that produce earthquakes, nearly as much energy is built up and released in slow motion—so slow it’s hard to measure. Scientists found evidence of one slow-slip event that went on for 32 years around Sumatra, before it finally gave way catastrophically, in the tragic earthquake of 1861. They discovered this by looking at old coral. In times of rising sea level, corals grow upward, seeking sunlight. In the waters around Sumatra, they found five times the coral growth rate over those three decades, revealing that the ocean floor beneath the reef was subsiding, as the Indo-Australian Plate slowly slipped beneath the Eurasian Plate. Understanding slow-slip events like this may one day allow scientists to better predict the earthquakes that often follow them.

The South Pole is the most inhospitable place on Earth—yet, each year, around 50 brave scientists and staff endure the winter there. Outside temperatures approach minus 120 degrees Fahrenheit in constant darkness. And they better hope nothing goes wrong. Because no one can come to help them. The South Pole is 800 miles from the nearest human contact. That’s farther than the International Space Station, which orbits less than 400 miles above Earth. From research bases on the Antarctic coast, it takes planes 5 to 8 hours to fly to the South Pole. But it’s so cold in winter that jet fuel turns to slush, meaning no flights can come or go. An over-land caravan of snow tractors in the summer takes 40 days. The sun is up in summer for more than 4,000 hours, one six-month-long day. At that time, the South Pole research station has its highest population, 200 scientists and staff. They study solar spots and atmospheric ozone, cosmic rays and neutrinos. Low temperatures still average negative 20 degrees Fahrenheit. In the fall, the sun nears the horizon for six weeks of dusk. Then it sets and is gone for three months for that seemingly endless night that is Antarctic winter. It takes a special person to endure the isolation, darkness, danger and lethal cold.

Landslides happen when a slope becomes unstable—because of denuding, from a fire or deforestation; over-steepening, from erosion or mining; overloading, from a reservoir or heavy snowpack; or oversaturation, with rain or melt water. So many things can cause a landslide that they happen in every U.S. state and nearly every country. When the slope gives way, soil can speed downhill at 50 to 100 miles an hour, carrying trees, boulders, cars, even houses. Earthquakes trigger just five percent of landslides. Twenty percent are caused by human activities, while three-quarters come from precipitation. Though some landslides happen suddenly, most give warning signs: cracks in pavement or soil, earth bulging at the base of a slope, water springs in new places. Your chances of getting caught in a slide are remote. But if you live in a landslide-prone area, keep these things in mind: Risk comes from uphill. You may want to move bedrooms or living areas to the downhill side of the house. If you suspect a slide is coming, open downhill windows and doors to allow debris that could pass through the house to exit. To escape a landslide, go up! Upstairs, and up on top of furniture, to have the best chance to stay on top of the debris. In the very unlikely event you’re trapped, never give up. Make noise so rescue teams can find you.

There’s an Irish saying, “There’s a pot of gold at the end of every rainbow.” But it used to say, “you’re as likely to find a pot of gold as the end of the rainbow.” That’s because if you go looking for its end, the rainbow vanishes. Rainbows occur when water droplets—from rain, mist, waterfalls, even sea spray—hang in the air. When sunlight enters the droplet, some will reflect off the back side and pass again out the front. As sunlight passes twice through the water, the different wavelengths that make it up bend at different angles, which splits the entering white light into the spectrum of rainbow colors. Your position, in relation to the sun and the water droplet, affects how much and which light reaches your eyes. Meaning, you determine how much rainbow you see. If the sun is directly behind you, and low in the sky, the largest amount of light is reflected back toward you, and you’ll see a strong rainbow. If the sun is 90 degrees to your right or left, you’ll see less reflected light and a weak rainbow. If the sun is high in the sky or on the other side of the water droplets, no light reflects back to you, and you’ll see no rainbow. This also means that, as you move, the amount of rainbow you see changes. If you travel far enough toward what appears to be its end, the rainbow, and your pot of gold, will gradually disappear.

Herbivores eat plants, and carnivores eat animals that eat plants, to get their energy. Plants and many bacteria create their own energy through photosynthesis, which depends on chlorophyll…which requires nitrogen. As we’ve described in other episodes, most nitrogen on Earth is in the form of N2, the inert nitrogen gas that won’t bond with other compounds, making it useless to plants. So, most plants rely on bacteria that cling to their roots and split the nitrogen in the soil for them. But when they can’t get enough, humans help them out, with nitrogen-rich fertilizers. Early fertilizers relied on naturally concentrated nitrogen. For instance, bat colonies eat insects, which contain nitrogen, then excrete nitrogen-rich droppings. For centuries, humans harvested tons of bat guano to fertilize our crops. But demand outstripped supply, so we had to invent a new source. At the start of the twentieth century, two German chemists devised a way to combine the nitrogen in air with hydrogen produced from natural gas to form ammonia, NH3. And their work won a Nobel prize… Because liquid ammonia could then be used to mass produce nitrogen-rich fertilizers. This drove the massive expansion of industrial agriculture—which has both created and allowed us to feed a growing global population.

In the 1800s, scientists found a 400-million-year-old fossil fish they thought could be the missing link between aquatic and land-dwelling creatures. They would have loved to study it, but it had gone extinct with the dinosaurs. Or so they thought. Until 1938, when a museum curator saw a fisherman haul one out of his net in South Africa. She wrote a hasty telegram to her museum. They wrote back: “Get that fish!” She had found the coelacanth, not extinct after all, but hiding for millions of years in the Indian Ocean. True to the fossil, it had small pectoral fins, on arm-like stalks, connected to joints like shoulders, and a wide fleshy tail. According to local reports, it was so oily and foul tasting that anyone who tried to eat it would become sick. Which probably helped this slow growing living fossil keep on living. And researchers soon found it’s very slow indeed. Coelacanths can grow to 200 pounds and live to 100 years but don’t reach sexual maturity until they hit 50. Females incubate eggs within their abdomen, which take 5 years to hatch, then emerge as live young—the longest gestation of any animal. It turns out, however, the coelacanth wasn’t the missing link that scientists hoped for. That honor belongs to its relative, the lungfish, which crawls out of the water to make short journeys on land.

There are no snakes in Ireland. Because, according to legend, St. Patrick expelled them. True, or folk tale? St. Patrick, ironically, wasn’t Irish. Or, named Patrick. He was born Maewyn Succat in 390 AD in Britain, kidnapped by pirates at 16, and held in slavery in Ireland for 6 years. He escaped and joined a monastery in England. Then decided to return to Ireland as a missionary, where he converted Druids and built the first church. He died in 460 AD in Downpatrick, hence the name. A few centuries later, he was recognized as Ireland’s patron saint for bringing Christianity to the land. A few centuries after that, his mythology had grown. Apparently, the snakes of Ireland once threatened him on a hilltop. He responded by beating a drum that drove them into the sea. Scholars believe this is a symbolic tale of Patrick purging Ireland of its pagan rituals. Scientists argue that Ireland never had snakes in the first place. In the last Ice Age, Ireland was covered in glaciers, much too cold for the cold-blooded creatures. Since the ice retreated, Ireland has been isolated by the frigid Irish sea. There are other isolated islands, like New Zealand and Hawaii, that don’t have snakes. And other cold regions, like Alaska and Northern Russia. So, it’s not as unusual as it sounds. But it makes for a good story over a green beer.

Tornadoes are mysterious. But on this EarthDate, we’ll try to unravel a few of their secrets. You’ve probably heard there’s a “tornado season” that happens in “tornado alley.” Well, not exactly. Tornadoes can happen almost anywhere—North and South America, Australia and New Zealand, South Africa, and the Indian subcontinent, where they’re most deadly due to higher population density. And they can happen any time. Most occur within a few months…but that depends on where you are. In the southeastern US, it’s January through March. In the central plains, April through June. In the Midwest, July through September. The only months they’re less frequent are October through December. Tornadoes appear to form from the cloud downward. But that’s not really the case. Researchers think most of them form horizontally, within the cloud, like a rolling barrel. Then an updraft turns them vertical, and they extend to the ground… Or not. Some scientists think they may form from the bottom up, as a swirling wind eddy on the ground reaches up to the cloud, connecting to and triggering that rolling barrel of wind. Or it could be some of each. But we can’t really tell by looking at radar since tornadoes form too quickly and too near the ground for our current technology to map them. Clearly, there’s still a lot of mystery surrounding tornadoes. But as research comes in, we’ll keep blowing it your way.

700 million years ago Earth froze over completely and stayed that way for millions of years. How did this deep freeze start, and how did it end? We think it went like this: At the time, all of Earth’s land was held in one large continent called Rodinia. As it began to break up, huge areas eroded, pulling carbon dioxide from the air and sequestering it in minerals. With CO2 dropping, the atmosphere cooled, and ice began forming in the polar oceans. As the ice sheets extended, their white surfaces reflected sunlight, which amplified the cooling. Soon the oceans were covered in ice, and Earth was frozen. The average surface temperature dropped to negative 60 degrees Fahrenheit. But beneath the ice, in what some believe to be the birth of plate tectonics, Earth was stirring. Rodinia kept pulling apart. Volcanos formed along its rift zones and began pumping out carbon dioxide and water vapor. Buildup of these greenhouse gases eventually drove runaway heating, which melted the glaciers. In just a few hundred years, global average temperatures rocketed to more than 120 degrees. The heat restarted the water cycle and drove weather systems that caused erosion, which consumed carbon dioxide. And Earth cooled again.  Thus began the constant cycling of Earth’s climate—and shortly thereafter, the explosion of life.

Sponges may look like plants, but they’re animals—some of the longest-lived on Earth, with a few living more than 10,000 years. They’re also the least evolutionarily advanced creatures on the planet. But new accidental findings may show we’ve underestimated them. Sponges evolved more than 500 million years ago, flourished through Earth’s great extinction events, and have endured ever since. Today there are 6,000 known species and new ones being identified regularly. Sponges were thought to be unresponsive to outside stimuli and, well, very plantlike. But that changed when it was revealed that sponges could move. Scientists studying undersea vents in one of the least hospitable places on Earth, in the cold blackness a mile beneath Arctic ice, found thousands of sponges living in the warmer water near the thermal vents. They set up specialized photography to look at vent activity but were amazed to see something else. The sponges were scuttling—very slowly—across the sea floor. Most of them had left tracks in the mud behind them, filled with protein crystals called spicules. Sponges have no muscles or apparent method of mobility. Why and how they do it is still a mystery. But this is a key part of science: looking for one thing and finding something else altogether new. Perhaps future expeditions will help us understand these and other hidden talents of sponges.

Penguins have been around a long, long time. They first evolved more than 60 million years ago when the asteroid that wiped out the dinosaurs opened a niche for them. Fossils suggest they were already flightless, but they took to the sea where they became perfectly adapted: Their feathers are coated in oil. Their body is insulated in fat. Their wings are shaped like flippers, making some penguins twice as fast as the fastest human swimmer. Their bowling-pin shape doesn’t look athletic, but in the water they’re a tuxedoed torpedo. That signature black and white coloring hides them from predators and prey. From above, they blend into the ocean darkness. From below, they look like the white sky. Though some early penguins stood as tall as a human, they’ve diversified into 17 different species, from the largest 80-pound Emperor to the tiny fairy penguin. Some species spend 75 percent of their time at sea—enough to grow barnacles on their feathers. Others can dive to 1,500 feet in search of food and hold their breath for half an hour! Each year around April 25th, the Adélie penguins of Antarctica begin a long migration from their summer breeding grounds to their winter feeding grounds. A few weeks later, their larger Antarctic cousins follow suit. So, scientists have designated April 25th as World Penguin Day. A good time to celebrate this weird and wonderful swimming bird.